Cutis

Increased understanding of the pathophysiology of psoriasis has been one of the driving forces in the development of new therapies. An understanding of the processes involved is important in the optimal management of the disease. The last 30 years of research and clinical practice have revolutionized our understanding of the pathogenesis of psoriasis as the dysregulation of immunity triggered by environmental and genetic stimuli. Psoriasis was originally regarded as a primary disorder of epidermal hyperproliferation. However, experimental models and clinical results from immunomodulating therapies have refined this perspective in conceptualizing psoriasis as a genetically programmed pathologic interaction among resident skin cells; infiltrating immunocytes; and a host of proinflammatory cytokines, chemokines, and growth factors produced by these immunocytes. Two populations of immunocytes and their respective signaling molecules collaborate in the pathogenesis: (1) innate immunocytes, mediated by antigen-presenting cells (APCs)(including natural killer [NK] T lymphocytes, Langerhans cells, and neutrophils), and (2) acquired or adaptive immunocytes, mediated by mature CD4⁺ and CD8⁺ T lymphocytes in the skin. Such dysregulation of immunity and subsequent inflammation is responsible for the development and perpetuation of the clinical plaques and histological inflammatory infiltrate characteristic of psoriasis.

Although psoriasis is considered to be an immune-mediated disease in which intralesional T lymphocytes and their proinflammatory signals trigger primed basal layer keratinocytes to rapidly proliferate, debate and research focus on the stimulus that incites this inflammatory process. Our current understanding considers psoriasis to be triggered by exogenous or endogenous environmental stimuli in genetically susceptible individuals. Such stimuli include group A streptococcal pharyngitis, viremia, allergic drug reactions, antimalarial drugs, lithium, beta-blockers, IFN-α, withdrawal of systemic corticosteroids, local trauma (Köbner phenomenon), and emotional stress. These stimuli correlate with the onset or flares of psoriatic lesions. Psoriasis genetics centers on susceptibility loci and corresponding candidate genes, particularly the psoriasis susceptibility (PSORS) 1 locus on the major histocompatibility complex (MHC) class I region. Current research on the pathogenesis of psoriasis examines the complex interactions among immunologic mechanisms, environmental stimuli, and genetic susceptibility. After discussing the clinical presentation and histopathologic features of psoriasis, we will review the pathophysiology of psoriasis through noteworthy developments, including serendipitous observations, reactions to therapies, clinical trials, and animal model systems that have shaped our view of the disease process. In addition to the classic skin lesions, approximately 23% of psoriasis patients develop psoriatic arthritis, with a 10-year latency after diagnosis of psoriasis.¹

Principles of Immunity

The immune system, intended to protect its host from foreign invaders and unregulated cell growth, employs 2 main effector pathways—the innate and the acquired (or adaptive) immune responses—both of which contribute to the pathophysiology of psoriasis.² Innate immunity responses occur within minutes to hours of antigen exposure but fail to develop memory for when the antigen is encountered again. However, adaptive immunity responses take days to weeks to respond after challenged with an antigen. The adaptive immune cells have the capacity to respond to a greater range of antigens and develop immunologic memory via rearrangement of antigen receptors on B and T cells. These specialized B and T cells can then be promptly mobilized and differentiated into mature effector cells that protect the host from a foreign pathogen.

Innate and adaptive immune responses are highly intertwined; they can initiate, perpetuate, and terminate the immune mechanisms responsible for inflammation. They can modify the nature of the immune response by altering the relative proportions of type 1 (T_H1), type 2 (T_H2), and the more recently discovered type 17 (T_H17) subset of helper T cells and their respective signaling molecules. A T_H1 response is essential for a cellular immunologic reaction to intracellular bacteria and viruses or cellular immunity. A T_H2 response promotes IgE synthesis, eosinophilia, and mast cell maturation for extracellular parasites and helminthes as well as humoral immunity, while a T_H17 response is important for cell-mediated immunity to extracellular bacteria and plays a role in autoimmunity.³ The innate and adaptive immune responses employ common effector molecules such as chemokines and cytokines, which are essential in mediating an immune response.

Implicating Dysregulation of Immunity

Our present appreciation of the pathogenesis of psoriasis is based on the history of trial-and-error therapies; serendipitous discoveries; and the current immune targeting drugs used in a variety of chronic inflammatory conditions, including rheumatoid arthritis, ankylosing spondylitis, and inflammatory bowel disease. Before the mid-1980s, research focused on the hyperproliferative epidermal cells as the primary pathology because a markedly thickened epidermis was indeed demonstrated on histologic specimens. Altered cell-cycle kinetics were thought to be the culprit behind the hyperkeratotic plaques. Thus, initial treatments centered on oncologic and antimitotic therapies used to arrest keratinocyte proliferation with agents such as arsenic, ammoniated mercury, and methotrexate.⁴

However, a paradigm shift from targeting epidermal keratinocytes to immunocyte populations was recognized when a patient receiving cyclosporine to prevent transplant rejection noted clearing of psoriatic lesions in the 1980s.⁵ Cyclosporine was observed to inhibit messenger RNA transcription of T-cell cytokines, thereby implicating immunologic dysregulation, specifically T-cell hyperactivity, in the pathogenesis of psoriasis.⁶ However, the concentrations of oral cyclosporine reached in the epidermis exerted direct effects on keratinocyte proliferation and lymphocyte function in these patients.⁷ Thus, the question was raised as to whether the keratinocytes or the lymphocytes drove the psoriatic plaques. The use of an IL-2 diphtheria toxin-fusion protein, denileukin diftitox, specific for activated T cells with high-affinity IL-2 receptors and nonreactive with keratinocytes, distinguished which cell type was responsible. This targeted T-cell toxin provided clinical and histological clearing of psoriatic plaques. Thus, T lymphocytes rather than keratinocytes were recognized as the definitive driver behind the psoriatic plaques.⁸

Additional studies have demonstrated that treatments that induce prolonged clearing of psoriatic lesions without continuous therapy, such as psoralen plus UVA irradiation, decreased the numbers of T cells in plaques by at least 90%.⁹ However, treatments that require continual therapy for satisfactory clinical results, such as cyclosporine and etretinate, simply suppress T-cell activity and proliferation.^10,11 Further evidence has linked cellular immunity with the pathogenesis of psoriasis, defining it as a T_H1-type disease. Natural killer T cells were shown to be involved through the use of a severe combined immunodeficient mouse model. They were injected into prepsoriatic skin grafted on immunodeficient mice, creating a psoriatic plaque with an immune response showing cytokines from T_H1 cells rather than T_H2 cells.¹² When psoriatic plaques were treated topically with the toll-like receptor 7 agonist imiquimod, aggravation and spreading of the plaques were noted. The exacerbation of psoriasis was accompanied by an induction of lesional T_H1-type interferon produced by plasmacytoid dendritic cell (DC) precursors. Plasmacytoid DCs were observed to compose up to 16% of the total dermal infiltrate in psoriatic skin lesions based on their coexpression of BDCA2 and CD123.¹³ Additionally, cancer patients being treated with interferon alfa experienced induction of psoriasis.¹⁴ Moreover, patients being treated for warts with intralesional interferon alfa developed psoriatic plaques in neighboring prior asymptomatic skin.¹⁵ Patients with psoriasis who were treated with interferon gamma, a T_H1 cytokine type, also developed new plaques correlating with the sites of injection.¹⁶

Intralesional T Lymphocytes

Psoriatic lesions contain a host of innate immunocytes, such as APCs, NK cells, and neutrophils, as well as adaptive T cells and an inflammatory infiltrate. These cells include CD4 and CD8 subtypes in which the CD8⁺ cells predominate in the epidermis, while CD4⁺ cells show preference for the dermis.¹⁷ There are 2 groups of CD8⁺ cells: one group migrates to the epidermis, expressing the integrin CD103, while the other group is found in the dermis but may be headed to or from the epidermis. The CD8⁺ cells residing in the epidermis that express the integrin CD103 are capable of interacting with E-cadherin, which enables these cells to travel to the epidermis and bind resident cells. Immunophenotyping reveals that these mature T cells represent chiefly activated memory cells, including CD2⁺, CD3⁺, CD5⁺, CLA, CD28, and CD45RO⁺.¹⁸ Many of these cells express activation markers such as HLA-DR, CD25, and CD27, in addition to the T-cell receptor (TCR).

T-Lymphocyte Stimulation

Both mature CD4⁺ and CD8⁺ T cells can respond to the peptides presented by APCs. Although the specific antigen that these T cells are reacting to has not yet been elucidated, several antigenic stimuli have been proposed, including self-proteins, microbial pathogens, and microbial superantigens. The premise that self-reactive T lymphocytes may contribute to the disease process is derived from the molecular mimicry theory in which an exuberant immune response to a pathogen produces cross-reactivity with self-antigens.¹⁹ Considering that infections have been associated with the onset of psoriasis, this theory merits consideration. However, it also has been observed that T cells can be activated without antigens or superantigens but rather with direct contact with accessory cells.²⁰ No single theory has clearly emerged. Researchers continue to search for the inciting stimulus that triggers the T lymphocyte and attempt to determine whether T cells are reacting to a self-derived or non–self-derived antigen.

T-Lymphocyte Signaling

T-cell signaling is a highly coordinated process in which T lymphocytes recognize antigens via presentation by mature APCs in the skin rather than the lymphoid tissues. Such APCs expose antigenic peptides via class I or II MHC molecules for which receptors are present on the T-cell surface. The antigen recognition complex at the T-cell and APC interface, in concert with a host of antigen-independent co-stimulatory signals, regulates T-cell signaling and is referred to as the immunologic synapse. The antigen presentation and network of co-stimulatory and adhesion molecules optimize T-cell activation, and dermal DCs release IL-12 and IL-23 to promote a T_H1 and T_H17 response, respectively. The growth factors released by these helper T cells sustain neoangiogenesis, stimulate epidermal hyperproliferation, alter epidermal differentiation, and decrease susceptibility to apoptosis that characterizes the erythematous hypertrophic scaling lesions of psoriasis.²¹ Furthermore, the cytokines produced from the immunologic response, such as tumor necrosis factor (TNF) α, IFN-γ, and IL-2, correspond to cytokines that are upregulated in psoriatic plaques.²²

Integral components of the immunologic synapse complex include co-stimulatory signals such as CD28, CD40, CD80, and CD86, as well as adhesion molecules such as cytotoxic T-lymphocyte antigen 4 and lymphocyte function-associated antigen (LFA) 1, which possess corresponding receptors on the T cell. These molecules play a key role in T-cell signaling, as their disruption has been shown to decrease T-cell responsiveness and associated inflammation. The B7 family of molecules routinely interacts with CD28 T cells to co-stimulate T-cell activation. Cytotoxic T-lymphocyte antigen 4 immunoglobulin, an antibody on the T-cell surface, targets B7 and interferes with signaling between B7 and CD28. In psoriatic patients, this blockade was demonstrated to attenuate the T-cell response and correlated with a clinical and histological decrease in psoriasiform hyperplasia.²³ Biologic therapies that disrupt the LFA-1 component of the immunologic synapse also have demonstrated efficacy in the treatment of psoriasis. Alefacept is a human LFA-3 fusion protein that binds CD2 on T cells and blocks the interaction between LFA-3 on APCs and CD2 on memory CD45RO⁺ T cells and induces apoptosis of such T cells. Efalizumab is a human monoclonal antibody to the CD11 chain of LFA-1 that blocks the interaction between LFA-1 on the T cell and intercellular adhesion molecule 1 on an APC or endothelial cell. Both alefacept and efalizumab, 2 formerly marketed biologic therapies, demonstrated remarkable clinical reduction of psoriatic lesions, and alefacept has been shown to produce disease remission for up to 18 months after discontinuation of therapy.^24-26

NK T Cells

Natural killer T cells represent a subset of CD3⁺ T cells present in psoriatic plaques. Although NK T cells possess a TCR, they differ from T cells by displaying NK receptors comprised of lectin and immunoglobulin families. These cells exhibit remarkable specificity and are activated upon recognition of glycolipids presented by CD1d molecules. This process occurs in contrast to CD4⁺ and CD8⁺ T cells, which, due to their TCR diversity, respond to peptides processed by APCs and displayed on MHC molecules. Natural killer T cells can be classified into 2 subsets: (1) one group that expresses CD4 and preferentially produces T_H1- versus T_H2-type cytokines, and (2) another group that lacks CD4 and CD8 that only produces T_H1-type cytokines. The innate immune system employs NK T cells early in the immune response because of their direct cytotoxicity and rapid production of cytokines such as IFN-γ, which promotes a T_H1 inflammatory response, and IL-4, which promotes the development of T_H2 cells. Excessive or dysfunctional NK T cells have been associated with autoimmune diseases such as multiple sclerosis and inflammatory bowel disease as well as allergic contact dermatitis.^27-29

In psoriasis, NK T cells are located in the epidermis, closely situated to epidermal keratinocytes, which suggests a role for direct antigen presentation. Furthermore, CD1d is overexpressed throughout the epidermis of psoriatic plaques, whereas normally CD1d expression is confined to terminally differentiated keratinocytes. An in vitro study examining cytokine-based inflammation demonstrative of psoriasis treated cultured CD1d-positive keratinocytes with interferon gamma in the presence of alpha-galactosylceramide of the lectin family.³⁰ Interferon gamma was observed to enhance keratinocyte CD1d expression, and subsequently, CD1d-positive keratinocytes were found to activate NK T cells to produce high levels of IFN-γ, while levels of IL-4 remained undetectable. The preferential production of IFN-γ supports a T_H1-mediated mechanism regulated by NK T cells in the immunopathogenesis of psoriasis.

Dendritic Cells

Dendritic cells are APCs that process antigens in the tissues in which they reside, after which they migrate to local lymph nodes where they present their native antigens to T cells. This process allows the T-cell response to be tailored to the appropriate antigens in the corresponding tissues. Immature DCs that capture antigens mature by migrating to the T-cell center of the lymph node where they present their antigens to either MHC molecules or the CD1 family. This presentation results in T-cell proliferation and differentiation that correlates with the required type of T-cell response. Multiple subsets of APCs, including myeloid and plasmacytoid DCs, are highly represented in the epidermis and dermis of psoriatic plaques as compared with normal skin.³¹ Dermal DCs are thought to be responsible for activating both the T_H1 and T_H17 infiltrate by secreting IL-12 and IL-23, respectively. This mixed cellular response secretes cytokines and leads to a cascade of events involving keratinocytes, fibroblasts, endothelial cells, and neutrophils that create the cutaneous lesions seen in psoriasis.³

Although DCs play a pivotal role in eliciting an immune response against a foreign invader, they also contribute to the establishment of tolerance. Throughout their maturation, DCs are continuously sensing their environment, which shapes their production of T_H1- versus T_H2-type cytokines and subsequently the nature of the T-cell response. When challenged with a virus, bacteria, or unchecked cell growth, DCs mature into APCs. However, in the absence of a strong stimulus, DCs fail to mature into APCs and present self-peptides with MHC molecules, thereby creating regulatory T cells involved in peripheral tolerance.³² If this balance between immunogenic APCs and housekeeping T cells is upset, inflammatory conditions such as psoriasis can result.

Cytokines

Cytokines are low-molecular-weight glycoproteins that function as signals to produce inflammation, defense, tissue repair and remodeling, fibrosis, angiogenesis, and restriction of neoplastic growth.³³ Cytokines are produced by immunocytes such as lymphocytes and macrophages as well as nonimmunocytes such as endothelial cells and keratinocytes. Proinflammatory cytokines include IL-1, IL-2, the IL-17 family, IFN-γ, and TNF-α, while anti-inflammatory cytokines include IL-4 and IL-10. A relative preponderance of T_H1 proinflammatory cytokines or an insufficiency of T_H2 anti-inflammatory cytokines induces local inflammation and recruitment of additional immunocyte populations, which produce added cytokines.³⁴ A vicious cycle of inflammation occurs that results in cutaneous manifestations such as a plaque. Psoriatic lesions are characterized by a relative increase of T_H1-type (eg, IL-2, IFN-γ, TNF-α, TNF-β) to T_H2-type (eg, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13) cytokines and an increase in T_H17-type cytokines. Natural killer T cells stimulated by CD1d-overexpressing keratinocytes increase production of proinflammatory IFN-γ without effect on the anti-inflammatory IL-4. In addition to the cytokines produced by T cells, APCs produce IL-18, IL-23, and TNF-α found in the inflammatory infiltrate of psoriatic plaques. Both IL-18 and IL-23 stimulate T_H1 cells to produce IFN-γ, and IL-23 stimulates T_H17 cells. Clearly, a T_H1- and T_H17-type pattern governs the immune effector cells and their respective cytokines present in psoriatic skin.

Tumor Necrosis Factor α

Although a network of cytokines is responsible for the inflammation of psoriasis, TNF-α has been implicated as a master proinflammatory cytokine of the innate immune response due to its widespread targets and sources. Tumor necrosis factor α is produced by activated T cells, keratinocytes, NK cells, macrophages, monocytes, Langerhans APCs, and endothelial cells. Psoriatic lesions demonstrate high concentrations of TNF-α, while the synovial fluid of psoriatic arthritis patients demonstrates elevated concentrations of TNF-α, IL-1, IL-6, and IL-8.³⁴ In psoriasis, TNF-α supports the expression of adhesion molecules (intercellular adhesion molecule 1 and P- and E-selectin), angiogenesis via vascular endothelial growth factor, the synthesis of proinflammatory molecules (IL-1, IL-6, IL-8, and nuclear factor κβ), and keratinocyte hyperproliferation via vasoactive intestinal peptide.³⁵

A role for TNF-α in psoriasis treatment was serendipitously discovered in a trial for Crohn disease in which infliximab, a mouse-human IgG1 anti–TNF-α monoclonal antibody, was observed to clear psoriatic plaques in a patient with both Crohn disease and psoriasis.³⁶ Immunotherapies that target TNF-α, including infliximab, etanercept, and adalimumab, demonstrate notable efficacy in the treatment of psoriasis.^37-39 Tumor necrosis factor α is regarded as the driver of the inflammatory cycle of psoriasis due to its numerous modes of production, capability to amplify other proinflammatory signals, and the efficacy and rapidity with which it produces clinical improvements in psoriasis.

IL-23/T_H17 Axis

A new distinct population of helper T cells has been shown to play an important role in psoriasis. These cells develop with the help of IL-23 (secreted by dermal DCs) and subsequently secrete cytokines such as IL-17; they are, therefore, named T_H17 cells. CD161 is considered a surface marker for these cells.⁴⁰ Strong evidence for this IL-23/T_H17 axis has been shown in mouse and human models as well as in genetic studies.

IL-23 is a cytokine that shares the p40 subunit with IL-12 and has been linked to autoimmune diseases in both mice and humans.³ It is required for optimal development of T_H17 cells⁴¹ from a committed CD4⁺ T-cell population after exposure to transforming growth factor β1 in combination with other proinflammatory cytokines.^42,43 IL-23 messenger RNA is produced at higher levels in inflammatory psoriatic skin lesions versus uninvolved skin,⁴⁴ and intradermal IL-23 injections in mice produced lesions resembling psoriasis macroscopically and microscopically.⁴⁵ Furthermore, several systemic therapies have been shown to modulate IL-23 levels and correlate with clinical benefit.³ Alterations in the gene for the IL-23 receptor have been shown to be protective for psoriasis,^46-48 and the gene coding for the p40 subunit is associated with psoriasis.^46,47

Type 17 helper T cells produce a number of cytokines, such as IL-22, IL-17A, IL-17F, and IL-26; the latter 3 are considered to be specific to this lineage.⁴² IL-22 acts on outer body barrier tissues, such as the skin, and has antimicrobial activity. Blocking the activity of IL-22 in mice prevented the development of skin lesions,⁴⁹ and psoriasis patients have elevated levels of IL-22 in the skin and blood.^50,51 The IL-17 cytokines induce the expression of proinflammatory cytokines, colony-stimulating factors, and chemokines, and they recruit, mobilize, and activate neutrophils.⁵² IL-17 messenger RNA was found in lesional psoriatic skin but not unaffected skin,⁵³ and cells isolated from the dermis of psoriatic skin have been shown to produce IL-17.⁵⁴ IL-17A is not elevated in the serum of psoriatic patients (unlike other autoimmune diseases),⁵⁵ and it is, therefore, thought that T_H17 cells and IL-17A production are localized to the affected psoriatic skin. Consistent with this concept is the finding that treatments such as cyclosporin A and anti-TNF agents decrease proinflammatory cytokines in lesional skin but not in the periphery.^56-58 These cytokines released by T_H17 cells in addition to those released by T_H1 cells act on keratinocytes and produce epidermal hyperproliferation, acanthosis, and hyperparakeratosis characteristic of psoriasis.³

New therapies have been developed to target the IL-23/T_H17 axis. Ustekinumab is approved for moderate to severe plaque psoriasis. This treatment’s effect may be sustained for up to 3 years, it is generally well tolerated, and it may be useful for patients refractory to anti-TNF therapy such as etanercept.⁵⁹ Briakinumab, another blocker of IL-12 and IL-23, was studied in phase 3 clinical trials, but its development was discontinued due to safety concerns.⁶⁰ Newer drugs targeting the IL-23/T_H17 axis include secukinumab, ixekizumab, brodalumab, guselkumab, and tildrakizumab.

Genetic Basis of Psoriasis

Psoriasis is a disease of overactive immunity in genetically susceptible individuals. Because patients exhibit varying skin phenotypes, extracutaneous manifestations, and disease courses, multiple genes resulting from linkage disequilibrium are believed to be involved in the pathogenesis of psoriasis. A decade of genome-wide linkage scans have established that PSORS1 is the strongest susceptibility locus demonstrable through family linkage studies; PSORS1 is responsible for up to 50% of the genetic component of psoriasis.⁶¹ More recently, HLA-Cw6 has received the most attention as a candidate gene of the PSORS1 susceptibility locus on the MHC class I region on chromosome 6p21.3.⁶² This gene may function in antigen presentation via MHC class I, which aids in the activation of the overactive T cells characteristic of psoriatic inflammation.

Studies involving the IL-23/T_H17 axis have shown genetics to play a role. Individuals may be protected from psoriasis with a nonsynonymous nucleotide substitution in the IL23R gene,^47-49 and certain haplotypes of the IL23R gene are associated with the disease^47,49 in addition to other autoimmune conditions.

Genomic scans have shown additional susceptibility loci for psoriasis on chromosomes 1q21, 3q21, 4q32-35, 16q12, and 17q25. Two regions on chromosome 17q were recently localized via mapping, which demonstrated a 6 megabase pairs separation, thereby indicating independent linkage factors. Genes SLC9A3R1 and NAT9 are present in the first region, while RAPTOR is demonstrated in the second region.⁶³SLC9A3R1 and NAT9 are players that regulate signal transduction, the immunologic synapse, and T-cell growth. RAPTOR is involved in T-cell function and growth pathways. Using these genes as an example, we can predict that the alterations of regulatory genes, even those yet undetermined, can enhance T-cell proliferation and inflammation manifested in psoriasis.

Conclusion

Psoriasis is a complex disease whereby multiple exogenous and endogenous stimuli incite already heightened innate immune responses in genetically predetermined individuals. The disease process is a result of a network of cell types, including T cells, DCs, and keratinocytes that, with the production of cytokines, generate a chronic inflammatory state. Our understanding of these cellular interactions and cytokines originates from developments, some meticulously planned, others serendipitous, in the fields of immunology, cell and molecular biology, and genetics. Such progress has fostered the creation of targeted immune therapy that has demonstrated remarkable efficacy in psoriasis treatment. Further study of the underlying pathophysiology of psoriasis may provide additional targets for therapy.

Increased understanding of the pathophysiology of psoriasis has been one of the driving forces in the development of new therapies. An understanding of the processes involved is important in the optimal management of the disease. The last 30 years of research and clinical practice have revolutionized our understanding of the pathogenesis of psoriasis as the dysregulation of immunity triggered by environmental and genetic stimuli. Psoriasis was originally regarded as a primary disorder of epidermal hyperproliferation. However, experimental models and clinical results from immunomodulating therapies have refined this perspective in conceptualizing psoriasis as a genetically programmed pathologic interaction among resident skin cells; infiltrating immunocytes; and a host of proinflammatory cytokines, chemokines, and growth factors produced by these immunocytes. Two populations of immunocytes and their respective signaling molecules collaborate in the pathogenesis: (1) innate immunocytes, mediated by antigen-presenting cells (APCs)(including natural killer [NK] T lymphocytes, Langerhans cells, and neutrophils), and (2) acquired or adaptive immunocytes, mediated by mature CD4⁺ and CD8⁺ T lymphocytes in the skin. Such dysregulation of immunity and subsequent inflammation is responsible for the development and perpetuation of the clinical plaques and histological inflammatory infiltrate characteristic of psoriasis.

Although psoriasis is considered to be an immune-mediated disease in which intralesional T lymphocytes and their proinflammatory signals trigger primed basal layer keratinocytes to rapidly proliferate, debate and research focus on the stimulus that incites this inflammatory process. Our current understanding considers psoriasis to be triggered by exogenous or endogenous environmental stimuli in genetically susceptible individuals. Such stimuli include group A streptococcal pharyngitis, viremia, allergic drug reactions, antimalarial drugs, lithium, beta-blockers, IFN-α, withdrawal of systemic corticosteroids, local trauma (Köbner phenomenon), and emotional stress. These stimuli correlate with the onset or flares of psoriatic lesions. Psoriasis genetics centers on susceptibility loci and corresponding candidate genes, particularly the psoriasis susceptibility (PSORS) 1 locus on the major histocompatibility complex (MHC) class I region. Current research on the pathogenesis of psoriasis examines the complex interactions among immunologic mechanisms, environmental stimuli, and genetic susceptibility. After discussing the clinical presentation and histopathologic features of psoriasis, we will review the pathophysiology of psoriasis through noteworthy developments, including serendipitous observations, reactions to therapies, clinical trials, and animal model systems that have shaped our view of the disease process. In addition to the classic skin lesions, approximately 23% of psoriasis patients develop psoriatic arthritis, with a 10-year latency after diagnosis of psoriasis.¹

Principles of Immunity

The immune system, intended to protect its host from foreign invaders and unregulated cell growth, employs 2 main effector pathways—the innate and the acquired (or adaptive) immune responses—both of which contribute to the pathophysiology of psoriasis.² Innate immunity responses occur within minutes to hours of antigen exposure but fail to develop memory for when the antigen is encountered again. However, adaptive immunity responses take days to weeks to respond after challenged with an antigen. The adaptive immune cells have the capacity to respond to a greater range of antigens and develop immunologic memory via rearrangement of antigen receptors on B and T cells. These specialized B and T cells can then be promptly mobilized and differentiated into mature effector cells that protect the host from a foreign pathogen.

Innate and adaptive immune responses are highly intertwined; they can initiate, perpetuate, and terminate the immune mechanisms responsible for inflammation. They can modify the nature of the immune response by altering the relative proportions of type 1 (T_H1), type 2 (T_H2), and the more recently discovered type 17 (T_H17) subset of helper T cells and their respective signaling molecules. A T_H1 response is essential for a cellular immunologic reaction to intracellular bacteria and viruses or cellular immunity. A T_H2 response promotes IgE synthesis, eosinophilia, and mast cell maturation for extracellular parasites and helminthes as well as humoral immunity, while a T_H17 response is important for cell-mediated immunity to extracellular bacteria and plays a role in autoimmunity.³ The innate and adaptive immune responses employ common effector molecules such as chemokines and cytokines, which are essential in mediating an immune response.

Implicating Dysregulation of Immunity

Our present appreciation of the pathogenesis of psoriasis is based on the history of trial-and-error therapies; serendipitous discoveries; and the current immune targeting drugs used in a variety of chronic inflammatory conditions, including rheumatoid arthritis, ankylosing spondylitis, and inflammatory bowel disease. Before the mid-1980s, research focused on the hyperproliferative epidermal cells as the primary pathology because a markedly thickened epidermis was indeed demonstrated on histologic specimens. Altered cell-cycle kinetics were thought to be the culprit behind the hyperkeratotic plaques. Thus, initial treatments centered on oncologic and antimitotic therapies used to arrest keratinocyte proliferation with agents such as arsenic, ammoniated mercury, and methotrexate.⁴

However, a paradigm shift from targeting epidermal keratinocytes to immunocyte populations was recognized when a patient receiving cyclosporine to prevent transplant rejection noted clearing of psoriatic lesions in the 1980s.⁵ Cyclosporine was observed to inhibit messenger RNA transcription of T-cell cytokines, thereby implicating immunologic dysregulation, specifically T-cell hyperactivity, in the pathogenesis of psoriasis.⁶ However, the concentrations of oral cyclosporine reached in the epidermis exerted direct effects on keratinocyte proliferation and lymphocyte function in these patients.⁷ Thus, the question was raised as to whether the keratinocytes or the lymphocytes drove the psoriatic plaques. The use of an IL-2 diphtheria toxin-fusion protein, denileukin diftitox, specific for activated T cells with high-affinity IL-2 receptors and nonreactive with keratinocytes, distinguished which cell type was responsible. This targeted T-cell toxin provided clinical and histological clearing of psoriatic plaques. Thus, T lymphocytes rather than keratinocytes were recognized as the definitive driver behind the psoriatic plaques.⁸

Additional studies have demonstrated that treatments that induce prolonged clearing of psoriatic lesions without continuous therapy, such as psoralen plus UVA irradiation, decreased the numbers of T cells in plaques by at least 90%.⁹ However, treatments that require continual therapy for satisfactory clinical results, such as cyclosporine and etretinate, simply suppress T-cell activity and proliferation.^10,11 Further evidence has linked cellular immunity with the pathogenesis of psoriasis, defining it as a T_H1-type disease. Natural killer T cells were shown to be involved through the use of a severe combined immunodeficient mouse model. They were injected into prepsoriatic skin grafted on immunodeficient mice, creating a psoriatic plaque with an immune response showing cytokines from T_H1 cells rather than T_H2 cells.¹² When psoriatic plaques were treated topically with the toll-like receptor 7 agonist imiquimod, aggravation and spreading of the plaques were noted. The exacerbation of psoriasis was accompanied by an induction of lesional T_H1-type interferon produced by plasmacytoid dendritic cell (DC) precursors. Plasmacytoid DCs were observed to compose up to 16% of the total dermal infiltrate in psoriatic skin lesions based on their coexpression of BDCA2 and CD123.¹³ Additionally, cancer patients being treated with interferon alfa experienced induction of psoriasis.¹⁴ Moreover, patients being treated for warts with intralesional interferon alfa developed psoriatic plaques in neighboring prior asymptomatic skin.¹⁵ Patients with psoriasis who were treated with interferon gamma, a T_H1 cytokine type, also developed new plaques correlating with the sites of injection.¹⁶

Intralesional T Lymphocytes

Psoriatic lesions contain a host of innate immunocytes, such as APCs, NK cells, and neutrophils, as well as adaptive T cells and an inflammatory infiltrate. These cells include CD4 and CD8 subtypes in which the CD8⁺ cells predominate in the epidermis, while CD4⁺ cells show preference for the dermis.¹⁷ There are 2 groups of CD8⁺ cells: one group migrates to the epidermis, expressing the integrin CD103, while the other group is found in the dermis but may be headed to or from the epidermis. The CD8⁺ cells residing in the epidermis that express the integrin CD103 are capable of interacting with E-cadherin, which enables these cells to travel to the epidermis and bind resident cells. Immunophenotyping reveals that these mature T cells represent chiefly activated memory cells, including CD2⁺, CD3⁺, CD5⁺, CLA, CD28, and CD45RO⁺.¹⁸ Many of these cells express activation markers such as HLA-DR, CD25, and CD27, in addition to the T-cell receptor (TCR).

T-Lymphocyte Stimulation

Both mature CD4⁺ and CD8⁺ T cells can respond to the peptides presented by APCs. Although the specific antigen that these T cells are reacting to has not yet been elucidated, several antigenic stimuli have been proposed, including self-proteins, microbial pathogens, and microbial superantigens. The premise that self-reactive T lymphocytes may contribute to the disease process is derived from the molecular mimicry theory in which an exuberant immune response to a pathogen produces cross-reactivity with self-antigens.¹⁹ Considering that infections have been associated with the onset of psoriasis, this theory merits consideration. However, it also has been observed that T cells can be activated without antigens or superantigens but rather with direct contact with accessory cells.²⁰ No single theory has clearly emerged. Researchers continue to search for the inciting stimulus that triggers the T lymphocyte and attempt to determine whether T cells are reacting to a self-derived or non–self-derived antigen.

T-Lymphocyte Signaling

T-cell signaling is a highly coordinated process in which T lymphocytes recognize antigens via presentation by mature APCs in the skin rather than the lymphoid tissues. Such APCs expose antigenic peptides via class I or II MHC molecules for which receptors are present on the T-cell surface. The antigen recognition complex at the T-cell and APC interface, in concert with a host of antigen-independent co-stimulatory signals, regulates T-cell signaling and is referred to as the immunologic synapse. The antigen presentation and network of co-stimulatory and adhesion molecules optimize T-cell activation, and dermal DCs release IL-12 and IL-23 to promote a T_H1 and T_H17 response, respectively. The growth factors released by these helper T cells sustain neoangiogenesis, stimulate epidermal hyperproliferation, alter epidermal differentiation, and decrease susceptibility to apoptosis that characterizes the erythematous hypertrophic scaling lesions of psoriasis.²¹ Furthermore, the cytokines produced from the immunologic response, such as tumor necrosis factor (TNF) α, IFN-γ, and IL-2, correspond to cytokines that are upregulated in psoriatic plaques.²²

Integral components of the immunologic synapse complex include co-stimulatory signals such as CD28, CD40, CD80, and CD86, as well as adhesion molecules such as cytotoxic T-lymphocyte antigen 4 and lymphocyte function-associated antigen (LFA) 1, which possess corresponding receptors on the T cell. These molecules play a key role in T-cell signaling, as their disruption has been shown to decrease T-cell responsiveness and associated inflammation. The B7 family of molecules routinely interacts with CD28 T cells to co-stimulate T-cell activation. Cytotoxic T-lymphocyte antigen 4 immunoglobulin, an antibody on the T-cell surface, targets B7 and interferes with signaling between B7 and CD28. In psoriatic patients, this blockade was demonstrated to attenuate the T-cell response and correlated with a clinical and histological decrease in psoriasiform hyperplasia.²³ Biologic therapies that disrupt the LFA-1 component of the immunologic synapse also have demonstrated efficacy in the treatment of psoriasis. Alefacept is a human LFA-3 fusion protein that binds CD2 on T cells and blocks the interaction between LFA-3 on APCs and CD2 on memory CD45RO⁺ T cells and induces apoptosis of such T cells. Efalizumab is a human monoclonal antibody to the CD11 chain of LFA-1 that blocks the interaction between LFA-1 on the T cell and intercellular adhesion molecule 1 on an APC or endothelial cell. Both alefacept and efalizumab, 2 formerly marketed biologic therapies, demonstrated remarkable clinical reduction of psoriatic lesions, and alefacept has been shown to produce disease remission for up to 18 months after discontinuation of therapy.^24-26

NK T Cells

Natural killer T cells represent a subset of CD3⁺ T cells present in psoriatic plaques. Although NK T cells possess a TCR, they differ from T cells by displaying NK receptors comprised of lectin and immunoglobulin families. These cells exhibit remarkable specificity and are activated upon recognition of glycolipids presented by CD1d molecules. This process occurs in contrast to CD4⁺ and CD8⁺ T cells, which, due to their TCR diversity, respond to peptides processed by APCs and displayed on MHC molecules. Natural killer T cells can be classified into 2 subsets: (1) one group that expresses CD4 and preferentially produces T_H1- versus T_H2-type cytokines, and (2) another group that lacks CD4 and CD8 that only produces T_H1-type cytokines. The innate immune system employs NK T cells early in the immune response because of their direct cytotoxicity and rapid production of cytokines such as IFN-γ, which promotes a T_H1 inflammatory response, and IL-4, which promotes the development of T_H2 cells. Excessive or dysfunctional NK T cells have been associated with autoimmune diseases such as multiple sclerosis and inflammatory bowel disease as well as allergic contact dermatitis.^27-29

In psoriasis, NK T cells are located in the epidermis, closely situated to epidermal keratinocytes, which suggests a role for direct antigen presentation. Furthermore, CD1d is overexpressed throughout the epidermis of psoriatic plaques, whereas normally CD1d expression is confined to terminally differentiated keratinocytes. An in vitro study examining cytokine-based inflammation demonstrative of psoriasis treated cultured CD1d-positive keratinocytes with interferon gamma in the presence of alpha-galactosylceramide of the lectin family.³⁰ Interferon gamma was observed to enhance keratinocyte CD1d expression, and subsequently, CD1d-positive keratinocytes were found to activate NK T cells to produce high levels of IFN-γ, while levels of IL-4 remained undetectable. The preferential production of IFN-γ supports a T_H1-mediated mechanism regulated by NK T cells in the immunopathogenesis of psoriasis.

Dendritic Cells

Dendritic cells are APCs that process antigens in the tissues in which they reside, after which they migrate to local lymph nodes where they present their native antigens to T cells. This process allows the T-cell response to be tailored to the appropriate antigens in the corresponding tissues. Immature DCs that capture antigens mature by migrating to the T-cell center of the lymph node where they present their antigens to either MHC molecules or the CD1 family. This presentation results in T-cell proliferation and differentiation that correlates with the required type of T-cell response. Multiple subsets of APCs, including myeloid and plasmacytoid DCs, are highly represented in the epidermis and dermis of psoriatic plaques as compared with normal skin.³¹ Dermal DCs are thought to be responsible for activating both the T_H1 and T_H17 infiltrate by secreting IL-12 and IL-23, respectively. This mixed cellular response secretes cytokines and leads to a cascade of events involving keratinocytes, fibroblasts, endothelial cells, and neutrophils that create the cutaneous lesions seen in psoriasis.³

Although DCs play a pivotal role in eliciting an immune response against a foreign invader, they also contribute to the establishment of tolerance. Throughout their maturation, DCs are continuously sensing their environment, which shapes their production of T_H1- versus T_H2-type cytokines and subsequently the nature of the T-cell response. When challenged with a virus, bacteria, or unchecked cell growth, DCs mature into APCs. However, in the absence of a strong stimulus, DCs fail to mature into APCs and present self-peptides with MHC molecules, thereby creating regulatory T cells involved in peripheral tolerance.³² If this balance between immunogenic APCs and housekeeping T cells is upset, inflammatory conditions such as psoriasis can result.

Cytokines

Cytokines are low-molecular-weight glycoproteins that function as signals to produce inflammation, defense, tissue repair and remodeling, fibrosis, angiogenesis, and restriction of neoplastic growth.³³ Cytokines are produced by immunocytes such as lymphocytes and macrophages as well as nonimmunocytes such as endothelial cells and keratinocytes. Proinflammatory cytokines include IL-1, IL-2, the IL-17 family, IFN-γ, and TNF-α, while anti-inflammatory cytokines include IL-4 and IL-10. A relative preponderance of T_H1 proinflammatory cytokines or an insufficiency of T_H2 anti-inflammatory cytokines induces local inflammation and recruitment of additional immunocyte populations, which produce added cytokines.³⁴ A vicious cycle of inflammation occurs that results in cutaneous manifestations such as a plaque. Psoriatic lesions are characterized by a relative increase of T_H1-type (eg, IL-2, IFN-γ, TNF-α, TNF-β) to T_H2-type (eg, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13) cytokines and an increase in T_H17-type cytokines. Natural killer T cells stimulated by CD1d-overexpressing keratinocytes increase production of proinflammatory IFN-γ without effect on the anti-inflammatory IL-4. In addition to the cytokines produced by T cells, APCs produce IL-18, IL-23, and TNF-α found in the inflammatory infiltrate of psoriatic plaques. Both IL-18 and IL-23 stimulate T_H1 cells to produce IFN-γ, and IL-23 stimulates T_H17 cells. Clearly, a T_H1- and T_H17-type pattern governs the immune effector cells and their respective cytokines present in psoriatic skin.

Tumor Necrosis Factor α

Although a network of cytokines is responsible for the inflammation of psoriasis, TNF-α has been implicated as a master proinflammatory cytokine of the innate immune response due to its widespread targets and sources. Tumor necrosis factor α is produced by activated T cells, keratinocytes, NK cells, macrophages, monocytes, Langerhans APCs, and endothelial cells. Psoriatic lesions demonstrate high concentrations of TNF-α, while the synovial fluid of psoriatic arthritis patients demonstrates elevated concentrations of TNF-α, IL-1, IL-6, and IL-8.³⁴ In psoriasis, TNF-α supports the expression of adhesion molecules (intercellular adhesion molecule 1 and P- and E-selectin), angiogenesis via vascular endothelial growth factor, the synthesis of proinflammatory molecules (IL-1, IL-6, IL-8, and nuclear factor κβ), and keratinocyte hyperproliferation via vasoactive intestinal peptide.³⁵

A role for TNF-α in psoriasis treatment was serendipitously discovered in a trial for Crohn disease in which infliximab, a mouse-human IgG1 anti–TNF-α monoclonal antibody, was observed to clear psoriatic plaques in a patient with both Crohn disease and psoriasis.³⁶ Immunotherapies that target TNF-α, including infliximab, etanercept, and adalimumab, demonstrate notable efficacy in the treatment of psoriasis.^37-39 Tumor necrosis factor α is regarded as the driver of the inflammatory cycle of psoriasis due to its numerous modes of production, capability to amplify other proinflammatory signals, and the efficacy and rapidity with which it produces clinical improvements in psoriasis.

IL-23/T_H17 Axis

A new distinct population of helper T cells has been shown to play an important role in psoriasis. These cells develop with the help of IL-23 (secreted by dermal DCs) and subsequently secrete cytokines such as IL-17; they are, therefore, named T_H17 cells. CD161 is considered a surface marker for these cells.⁴⁰ Strong evidence for this IL-23/T_H17 axis has been shown in mouse and human models as well as in genetic studies.

IL-23 is a cytokine that shares the p40 subunit with IL-12 and has been linked to autoimmune diseases in both mice and humans.³ It is required for optimal development of T_H17 cells⁴¹ from a committed CD4⁺ T-cell population after exposure to transforming growth factor β1 in combination with other proinflammatory cytokines.^42,43 IL-23 messenger RNA is produced at higher levels in inflammatory psoriatic skin lesions versus uninvolved skin,⁴⁴ and intradermal IL-23 injections in mice produced lesions resembling psoriasis macroscopically and microscopically.⁴⁵ Furthermore, several systemic therapies have been shown to modulate IL-23 levels and correlate with clinical benefit.³ Alterations in the gene for the IL-23 receptor have been shown to be protective for psoriasis,^46-48 and the gene coding for the p40 subunit is associated with psoriasis.^46,47

Type 17 helper T cells produce a number of cytokines, such as IL-22, IL-17A, IL-17F, and IL-26; the latter 3 are considered to be specific to this lineage.⁴² IL-22 acts on outer body barrier tissues, such as the skin, and has antimicrobial activity. Blocking the activity of IL-22 in mice prevented the development of skin lesions,⁴⁹ and psoriasis patients have elevated levels of IL-22 in the skin and blood.^50,51 The IL-17 cytokines induce the expression of proinflammatory cytokines, colony-stimulating factors, and chemokines, and they recruit, mobilize, and activate neutrophils.⁵² IL-17 messenger RNA was found in lesional psoriatic skin but not unaffected skin,⁵³ and cells isolated from the dermis of psoriatic skin have been shown to produce IL-17.⁵⁴ IL-17A is not elevated in the serum of psoriatic patients (unlike other autoimmune diseases),⁵⁵ and it is, therefore, thought that T_H17 cells and IL-17A production are localized to the affected psoriatic skin. Consistent with this concept is the finding that treatments such as cyclosporin A and anti-TNF agents decrease proinflammatory cytokines in lesional skin but not in the periphery.^56-58 These cytokines released by T_H17 cells in addition to those released by T_H1 cells act on keratinocytes and produce epidermal hyperproliferation, acanthosis, and hyperparakeratosis characteristic of psoriasis.³

New therapies have been developed to target the IL-23/T_H17 axis. Ustekinumab is approved for moderate to severe plaque psoriasis. This treatment’s effect may be sustained for up to 3 years, it is generally well tolerated, and it may be useful for patients refractory to anti-TNF therapy such as etanercept.⁵⁹ Briakinumab, another blocker of IL-12 and IL-23, was studied in phase 3 clinical trials, but its development was discontinued due to safety concerns.⁶⁰ Newer drugs targeting the IL-23/T_H17 axis include secukinumab, ixekizumab, brodalumab, guselkumab, and tildrakizumab.

Genetic Basis of Psoriasis

Psoriasis is a disease of overactive immunity in genetically susceptible individuals. Because patients exhibit varying skin phenotypes, extracutaneous manifestations, and disease courses, multiple genes resulting from linkage disequilibrium are believed to be involved in the pathogenesis of psoriasis. A decade of genome-wide linkage scans have established that PSORS1 is the strongest susceptibility locus demonstrable through family linkage studies; PSORS1 is responsible for up to 50% of the genetic component of psoriasis.⁶¹ More recently, HLA-Cw6 has received the most attention as a candidate gene of the PSORS1 susceptibility locus on the MHC class I region on chromosome 6p21.3.⁶² This gene may function in antigen presentation via MHC class I, which aids in the activation of the overactive T cells characteristic of psoriatic inflammation.

Studies involving the IL-23/T_H17 axis have shown genetics to play a role. Individuals may be protected from psoriasis with a nonsynonymous nucleotide substitution in the IL23R gene,^47-49 and certain haplotypes of the IL23R gene are associated with the disease^47,49 in addition to other autoimmune conditions.

Genomic scans have shown additional susceptibility loci for psoriasis on chromosomes 1q21, 3q21, 4q32-35, 16q12, and 17q25. Two regions on chromosome 17q were recently localized via mapping, which demonstrated a 6 megabase pairs separation, thereby indicating independent linkage factors. Genes SLC9A3R1 and NAT9 are present in the first region, while RAPTOR is demonstrated in the second region.⁶³SLC9A3R1 and NAT9 are players that regulate signal transduction, the immunologic synapse, and T-cell growth. RAPTOR is involved in T-cell function and growth pathways. Using these genes as an example, we can predict that the alterations of regulatory genes, even those yet undetermined, can enhance T-cell proliferation and inflammation manifested in psoriasis.

Conclusion

Psoriasis is a complex disease whereby multiple exogenous and endogenous stimuli incite already heightened innate immune responses in genetically predetermined individuals. The disease process is a result of a network of cell types, including T cells, DCs, and keratinocytes that, with the production of cytokines, generate a chronic inflammatory state. Our understanding of these cellular interactions and cytokines originates from developments, some meticulously planned, others serendipitous, in the fields of immunology, cell and molecular biology, and genetics. Such progress has fostered the creation of targeted immune therapy that has demonstrated remarkable efficacy in psoriasis treatment. Further study of the underlying pathophysiology of psoriasis may provide additional targets for therapy.

Increased understanding of the pathophysiology of psoriasis has been one of the driving forces in the development of new therapies. An understanding of the processes involved is important in the optimal management of the disease. The last 30 years of research and clinical practice have revolutionized our understanding of the pathogenesis of psoriasis as the dysregulation of immunity triggered by environmental and genetic stimuli. Psoriasis was originally regarded as a primary disorder of epidermal hyperproliferation. However, experimental models and clinical results from immunomodulating therapies have refined this perspective in conceptualizing psoriasis as a genetically programmed pathologic interaction among resident skin cells; infiltrating immunocytes; and a host of proinflammatory cytokines, chemokines, and growth factors produced by these immunocytes. Two populations of immunocytes and their respective signaling molecules collaborate in the pathogenesis: (1) innate immunocytes, mediated by antigen-presenting cells (APCs)(including natural killer [NK] T lymphocytes, Langerhans cells, and neutrophils), and (2) acquired or adaptive immunocytes, mediated by mature CD4⁺ and CD8⁺ T lymphocytes in the skin. Such dysregulation of immunity and subsequent inflammation is responsible for the development and perpetuation of the clinical plaques and histological inflammatory infiltrate characteristic of psoriasis.

Although psoriasis is considered to be an immune-mediated disease in which intralesional T lymphocytes and their proinflammatory signals trigger primed basal layer keratinocytes to rapidly proliferate, debate and research focus on the stimulus that incites this inflammatory process. Our current understanding considers psoriasis to be triggered by exogenous or endogenous environmental stimuli in genetically susceptible individuals. Such stimuli include group A streptococcal pharyngitis, viremia, allergic drug reactions, antimalarial drugs, lithium, beta-blockers, IFN-α, withdrawal of systemic corticosteroids, local trauma (Köbner phenomenon), and emotional stress. These stimuli correlate with the onset or flares of psoriatic lesions. Psoriasis genetics centers on susceptibility loci and corresponding candidate genes, particularly the psoriasis susceptibility (PSORS) 1 locus on the major histocompatibility complex (MHC) class I region. Current research on the pathogenesis of psoriasis examines the complex interactions among immunologic mechanisms, environmental stimuli, and genetic susceptibility. After discussing the clinical presentation and histopathologic features of psoriasis, we will review the pathophysiology of psoriasis through noteworthy developments, including serendipitous observations, reactions to therapies, clinical trials, and animal model systems that have shaped our view of the disease process. In addition to the classic skin lesions, approximately 23% of psoriasis patients develop psoriatic arthritis, with a 10-year latency after diagnosis of psoriasis.¹

Principles of Immunity

The immune system, intended to protect its host from foreign invaders and unregulated cell growth, employs 2 main effector pathways—the innate and the acquired (or adaptive) immune responses—both of which contribute to the pathophysiology of psoriasis.² Innate immunity responses occur within minutes to hours of antigen exposure but fail to develop memory for when the antigen is encountered again. However, adaptive immunity responses take days to weeks to respond after challenged with an antigen. The adaptive immune cells have the capacity to respond to a greater range of antigens and develop immunologic memory via rearrangement of antigen receptors on B and T cells. These specialized B and T cells can then be promptly mobilized and differentiated into mature effector cells that protect the host from a foreign pathogen.

Innate and adaptive immune responses are highly intertwined; they can initiate, perpetuate, and terminate the immune mechanisms responsible for inflammation. They can modify the nature of the immune response by altering the relative proportions of type 1 (T_H1), type 2 (T_H2), and the more recently discovered type 17 (T_H17) subset of helper T cells and their respective signaling molecules. A T_H1 response is essential for a cellular immunologic reaction to intracellular bacteria and viruses or cellular immunity. A T_H2 response promotes IgE synthesis, eosinophilia, and mast cell maturation for extracellular parasites and helminthes as well as humoral immunity, while a T_H17 response is important for cell-mediated immunity to extracellular bacteria and plays a role in autoimmunity.³ The innate and adaptive immune responses employ common effector molecules such as chemokines and cytokines, which are essential in mediating an immune response.

Implicating Dysregulation of Immunity

Our present appreciation of the pathogenesis of psoriasis is based on the history of trial-and-error therapies; serendipitous discoveries; and the current immune targeting drugs used in a variety of chronic inflammatory conditions, including rheumatoid arthritis, ankylosing spondylitis, and inflammatory bowel disease. Before the mid-1980s, research focused on the hyperproliferative epidermal cells as the primary pathology because a markedly thickened epidermis was indeed demonstrated on histologic specimens. Altered cell-cycle kinetics were thought to be the culprit behind the hyperkeratotic plaques. Thus, initial treatments centered on oncologic and antimitotic therapies used to arrest keratinocyte proliferation with agents such as arsenic, ammoniated mercury, and methotrexate.⁴

However, a paradigm shift from targeting epidermal keratinocytes to immunocyte populations was recognized when a patient receiving cyclosporine to prevent transplant rejection noted clearing of psoriatic lesions in the 1980s.⁵ Cyclosporine was observed to inhibit messenger RNA transcription of T-cell cytokines, thereby implicating immunologic dysregulation, specifically T-cell hyperactivity, in the pathogenesis of psoriasis.⁶ However, the concentrations of oral cyclosporine reached in the epidermis exerted direct effects on keratinocyte proliferation and lymphocyte function in these patients.⁷ Thus, the question was raised as to whether the keratinocytes or the lymphocytes drove the psoriatic plaques. The use of an IL-2 diphtheria toxin-fusion protein, denileukin diftitox, specific for activated T cells with high-affinity IL-2 receptors and nonreactive with keratinocytes, distinguished which cell type was responsible. This targeted T-cell toxin provided clinical and histological clearing of psoriatic plaques. Thus, T lymphocytes rather than keratinocytes were recognized as the definitive driver behind the psoriatic plaques.⁸

Additional studies have demonstrated that treatments that induce prolonged clearing of psoriatic lesions without continuous therapy, such as psoralen plus UVA irradiation, decreased the numbers of T cells in plaques by at least 90%.⁹ However, treatments that require continual therapy for satisfactory clinical results, such as cyclosporine and etretinate, simply suppress T-cell activity and proliferation.^10,11 Further evidence has linked cellular immunity with the pathogenesis of psoriasis, defining it as a T_H1-type disease. Natural killer T cells were shown to be involved through the use of a severe combined immunodeficient mouse model. They were injected into prepsoriatic skin grafted on immunodeficient mice, creating a psoriatic plaque with an immune response showing cytokines from T_H1 cells rather than T_H2 cells.¹² When psoriatic plaques were treated topically with the toll-like receptor 7 agonist imiquimod, aggravation and spreading of the plaques were noted. The exacerbation of psoriasis was accompanied by an induction of lesional T_H1-type interferon produced by plasmacytoid dendritic cell (DC) precursors. Plasmacytoid DCs were observed to compose up to 16% of the total dermal infiltrate in psoriatic skin lesions based on their coexpression of BDCA2 and CD123.¹³ Additionally, cancer patients being treated with interferon alfa experienced induction of psoriasis.¹⁴ Moreover, patients being treated for warts with intralesional interferon alfa developed psoriatic plaques in neighboring prior asymptomatic skin.¹⁵ Patients with psoriasis who were treated with interferon gamma, a T_H1 cytokine type, also developed new plaques correlating with the sites of injection.¹⁶

Intralesional T Lymphocytes

Psoriatic lesions contain a host of innate immunocytes, such as APCs, NK cells, and neutrophils, as well as adaptive T cells and an inflammatory infiltrate. These cells include CD4 and CD8 subtypes in which the CD8⁺ cells predominate in the epidermis, while CD4⁺ cells show preference for the dermis.¹⁷ There are 2 groups of CD8⁺ cells: one group migrates to the epidermis, expressing the integrin CD103, while the other group is found in the dermis but may be headed to or from the epidermis. The CD8⁺ cells residing in the epidermis that express the integrin CD103 are capable of interacting with E-cadherin, which enables these cells to travel to the epidermis and bind resident cells. Immunophenotyping reveals that these mature T cells represent chiefly activated memory cells, including CD2⁺, CD3⁺, CD5⁺, CLA, CD28, and CD45RO⁺.¹⁸ Many of these cells express activation markers such as HLA-DR, CD25, and CD27, in addition to the T-cell receptor (TCR).

T-Lymphocyte Stimulation

Both mature CD4⁺ and CD8⁺ T cells can respond to the peptides presented by APCs. Although the specific antigen that these T cells are reacting to has not yet been elucidated, several antigenic stimuli have been proposed, including self-proteins, microbial pathogens, and microbial superantigens. The premise that self-reactive T lymphocytes may contribute to the disease process is derived from the molecular mimicry theory in which an exuberant immune response to a pathogen produces cross-reactivity with self-antigens.¹⁹ Considering that infections have been associated with the onset of psoriasis, this theory merits consideration. However, it also has been observed that T cells can be activated without antigens or superantigens but rather with direct contact with accessory cells.²⁰ No single theory has clearly emerged. Researchers continue to search for the inciting stimulus that triggers the T lymphocyte and attempt to determine whether T cells are reacting to a self-derived or non–self-derived antigen.

T-Lymphocyte Signaling

T-cell signaling is a highly coordinated process in which T lymphocytes recognize antigens via presentation by mature APCs in the skin rather than the lymphoid tissues. Such APCs expose antigenic peptides via class I or II MHC molecules for which receptors are present on the T-cell surface. The antigen recognition complex at the T-cell and APC interface, in concert with a host of antigen-independent co-stimulatory signals, regulates T-cell signaling and is referred to as the immunologic synapse. The antigen presentation and network of co-stimulatory and adhesion molecules optimize T-cell activation, and dermal DCs release IL-12 and IL-23 to promote a T_H1 and T_H17 response, respectively. The growth factors released by these helper T cells sustain neoangiogenesis, stimulate epidermal hyperproliferation, alter epidermal differentiation, and decrease susceptibility to apoptosis that characterizes the erythematous hypertrophic scaling lesions of psoriasis.²¹ Furthermore, the cytokines produced from the immunologic response, such as tumor necrosis factor (TNF) α, IFN-γ, and IL-2, correspond to cytokines that are upregulated in psoriatic plaques.²²

Integral components of the immunologic synapse complex include co-stimulatory signals such as CD28, CD40, CD80, and CD86, as well as adhesion molecules such as cytotoxic T-lymphocyte antigen 4 and lymphocyte function-associated antigen (LFA) 1, which possess corresponding receptors on the T cell. These molecules play a key role in T-cell signaling, as their disruption has been shown to decrease T-cell responsiveness and associated inflammation. The B7 family of molecules routinely interacts with CD28 T cells to co-stimulate T-cell activation. Cytotoxic T-lymphocyte antigen 4 immunoglobulin, an antibody on the T-cell surface, targets B7 and interferes with signaling between B7 and CD28. In psoriatic patients, this blockade was demonstrated to attenuate the T-cell response and correlated with a clinical and histological decrease in psoriasiform hyperplasia.²³ Biologic therapies that disrupt the LFA-1 component of the immunologic synapse also have demonstrated efficacy in the treatment of psoriasis. Alefacept is a human LFA-3 fusion protein that binds CD2 on T cells and blocks the interaction between LFA-3 on APCs and CD2 on memory CD45RO⁺ T cells and induces apoptosis of such T cells. Efalizumab is a human monoclonal antibody to the CD11 chain of LFA-1 that blocks the interaction between LFA-1 on the T cell and intercellular adhesion molecule 1 on an APC or endothelial cell. Both alefacept and efalizumab, 2 formerly marketed biologic therapies, demonstrated remarkable clinical reduction of psoriatic lesions, and alefacept has been shown to produce disease remission for up to 18 months after discontinuation of therapy.^24-26

NK T Cells

Natural killer T cells represent a subset of CD3⁺ T cells present in psoriatic plaques. Although NK T cells possess a TCR, they differ from T cells by displaying NK receptors comprised of lectin and immunoglobulin families. These cells exhibit remarkable specificity and are activated upon recognition of glycolipids presented by CD1d molecules. This process occurs in contrast to CD4⁺ and CD8⁺ T cells, which, due to their TCR diversity, respond to peptides processed by APCs and displayed on MHC molecules. Natural killer T cells can be classified into 2 subsets: (1) one group that expresses CD4 and preferentially produces T_H1- versus T_H2-type cytokines, and (2) another group that lacks CD4 and CD8 that only produces T_H1-type cytokines. The innate immune system employs NK T cells early in the immune response because of their direct cytotoxicity and rapid production of cytokines such as IFN-γ, which promotes a T_H1 inflammatory response, and IL-4, which promotes the development of T_H2 cells. Excessive or dysfunctional NK T cells have been associated with autoimmune diseases such as multiple sclerosis and inflammatory bowel disease as well as allergic contact dermatitis.^27-29

In psoriasis, NK T cells are located in the epidermis, closely situated to epidermal keratinocytes, which suggests a role for direct antigen presentation. Furthermore, CD1d is overexpressed throughout the epidermis of psoriatic plaques, whereas normally CD1d expression is confined to terminally differentiated keratinocytes. An in vitro study examining cytokine-based inflammation demonstrative of psoriasis treated cultured CD1d-positive keratinocytes with interferon gamma in the presence of alpha-galactosylceramide of the lectin family.³⁰ Interferon gamma was observed to enhance keratinocyte CD1d expression, and subsequently, CD1d-positive keratinocytes were found to activate NK T cells to produce high levels of IFN-γ, while levels of IL-4 remained undetectable. The preferential production of IFN-γ supports a T_H1-mediated mechanism regulated by NK T cells in the immunopathogenesis of psoriasis.

Dendritic Cells

Dendritic cells are APCs that process antigens in the tissues in which they reside, after which they migrate to local lymph nodes where they present their native antigens to T cells. This process allows the T-cell response to be tailored to the appropriate antigens in the corresponding tissues. Immature DCs that capture antigens mature by migrating to the T-cell center of the lymph node where they present their antigens to either MHC molecules or the CD1 family. This presentation results in T-cell proliferation and differentiation that correlates with the required type of T-cell response. Multiple subsets of APCs, including myeloid and plasmacytoid DCs, are highly represented in the epidermis and dermis of psoriatic plaques as compared with normal skin.³¹ Dermal DCs are thought to be responsible for activating both the T_H1 and T_H17 infiltrate by secreting IL-12 and IL-23, respectively. This mixed cellular response secretes cytokines and leads to a cascade of events involving keratinocytes, fibroblasts, endothelial cells, and neutrophils that create the cutaneous lesions seen in psoriasis.³

Although DCs play a pivotal role in eliciting an immune response against a foreign invader, they also contribute to the establishment of tolerance. Throughout their maturation, DCs are continuously sensing their environment, which shapes their production of T_H1- versus T_H2-type cytokines and subsequently the nature of the T-cell response. When challenged with a virus, bacteria, or unchecked cell growth, DCs mature into APCs. However, in the absence of a strong stimulus, DCs fail to mature into APCs and present self-peptides with MHC molecules, thereby creating regulatory T cells involved in peripheral tolerance.³² If this balance between immunogenic APCs and housekeeping T cells is upset, inflammatory conditions such as psoriasis can result.

Cytokines

Cytokines are low-molecular-weight glycoproteins that function as signals to produce inflammation, defense, tissue repair and remodeling, fibrosis, angiogenesis, and restriction of neoplastic growth.³³ Cytokines are produced by immunocytes such as lymphocytes and macrophages as well as nonimmunocytes such as endothelial cells and keratinocytes. Proinflammatory cytokines include IL-1, IL-2, the IL-17 family, IFN-γ, and TNF-α, while anti-inflammatory cytokines include IL-4 and IL-10. A relative preponderance of T_H1 proinflammatory cytokines or an insufficiency of T_H2 anti-inflammatory cytokines induces local inflammation and recruitment of additional immunocyte populations, which produce added cytokines.³⁴ A vicious cycle of inflammation occurs that results in cutaneous manifestations such as a plaque. Psoriatic lesions are characterized by a relative increase of T_H1-type (eg, IL-2, IFN-γ, TNF-α, TNF-β) to T_H2-type (eg, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13) cytokines and an increase in T_H17-type cytokines. Natural killer T cells stimulated by CD1d-overexpressing keratinocytes increase production of proinflammatory IFN-γ without effect on the anti-inflammatory IL-4. In addition to the cytokines produced by T cells, APCs produce IL-18, IL-23, and TNF-α found in the inflammatory infiltrate of psoriatic plaques. Both IL-18 and IL-23 stimulate T_H1 cells to produce IFN-γ, and IL-23 stimulates T_H17 cells. Clearly, a T_H1- and T_H17-type pattern governs the immune effector cells and their respective cytokines present in psoriatic skin.

Tumor Necrosis Factor α

Although a network of cytokines is responsible for the inflammation of psoriasis, TNF-α has been implicated as a master proinflammatory cytokine of the innate immune response due to its widespread targets and sources. Tumor necrosis factor α is produced by activated T cells, keratinocytes, NK cells, macrophages, monocytes, Langerhans APCs, and endothelial cells. Psoriatic lesions demonstrate high concentrations of TNF-α, while the synovial fluid of psoriatic arthritis patients demonstrates elevated concentrations of TNF-α, IL-1, IL-6, and IL-8.³⁴ In psoriasis, TNF-α supports the expression of adhesion molecules (intercellular adhesion molecule 1 and P- and E-selectin), angiogenesis via vascular endothelial growth factor, the synthesis of proinflammatory molecules (IL-1, IL-6, IL-8, and nuclear factor κβ), and keratinocyte hyperproliferation via vasoactive intestinal peptide.³⁵

A role for TNF-α in psoriasis treatment was serendipitously discovered in a trial for Crohn disease in which infliximab, a mouse-human IgG1 anti–TNF-α monoclonal antibody, was observed to clear psoriatic plaques in a patient with both Crohn disease and psoriasis.³⁶ Immunotherapies that target TNF-α, including infliximab, etanercept, and adalimumab, demonstrate notable efficacy in the treatment of psoriasis.^37-39 Tumor necrosis factor α is regarded as the driver of the inflammatory cycle of psoriasis due to its numerous modes of production, capability to amplify other proinflammatory signals, and the efficacy and rapidity with which it produces clinical improvements in psoriasis.

IL-23/T_H17 Axis

A new distinct population of helper T cells has been shown to play an important role in psoriasis. These cells develop with the help of IL-23 (secreted by dermal DCs) and subsequently secrete cytokines such as IL-17; they are, therefore, named T_H17 cells. CD161 is considered a surface marker for these cells.⁴⁰ Strong evidence for this IL-23/T_H17 axis has been shown in mouse and human models as well as in genetic studies.

IL-23 is a cytokine that shares the p40 subunit with IL-12 and has been linked to autoimmune diseases in both mice and humans.³ It is required for optimal development of T_H17 cells⁴¹ from a committed CD4⁺ T-cell population after exposure to transforming growth factor β1 in combination with other proinflammatory cytokines.^42,43 IL-23 messenger RNA is produced at higher levels in inflammatory psoriatic skin lesions versus uninvolved skin,⁴⁴ and intradermal IL-23 injections in mice produced lesions resembling psoriasis macroscopically and microscopically.⁴⁵ Furthermore, several systemic therapies have been shown to modulate IL-23 levels and correlate with clinical benefit.³ Alterations in the gene for the IL-23 receptor have been shown to be protective for psoriasis,^46-48 and the gene coding for the p40 subunit is associated with psoriasis.^46,47

Type 17 helper T cells produce a number of cytokines, such as IL-22, IL-17A, IL-17F, and IL-26; the latter 3 are considered to be specific to this lineage.⁴² IL-22 acts on outer body barrier tissues, such as the skin, and has antimicrobial activity. Blocking the activity of IL-22 in mice prevented the development of skin lesions,⁴⁹ and psoriasis patients have elevated levels of IL-22 in the skin and blood.^50,51 The IL-17 cytokines induce the expression of proinflammatory cytokines, colony-stimulating factors, and chemokines, and they recruit, mobilize, and activate neutrophils.⁵² IL-17 messenger RNA was found in lesional psoriatic skin but not unaffected skin,⁵³ and cells isolated from the dermis of psoriatic skin have been shown to produce IL-17.⁵⁴ IL-17A is not elevated in the serum of psoriatic patients (unlike other autoimmune diseases),⁵⁵ and it is, therefore, thought that T_H17 cells and IL-17A production are localized to the affected psoriatic skin. Consistent with this concept is the finding that treatments such as cyclosporin A and anti-TNF agents decrease proinflammatory cytokines in lesional skin but not in the periphery.^56-58 These cytokines released by T_H17 cells in addition to those released by T_H1 cells act on keratinocytes and produce epidermal hyperproliferation, acanthosis, and hyperparakeratosis characteristic of psoriasis.³

New therapies have been developed to target the IL-23/T_H17 axis. Ustekinumab is approved for moderate to severe plaque psoriasis. This treatment’s effect may be sustained for up to 3 years, it is generally well tolerated, and it may be useful for patients refractory to anti-TNF therapy such as etanercept.⁵⁹ Briakinumab, another blocker of IL-12 and IL-23, was studied in phase 3 clinical trials, but its development was discontinued due to safety concerns.⁶⁰ Newer drugs targeting the IL-23/T_H17 axis include secukinumab, ixekizumab, brodalumab, guselkumab, and tildrakizumab.

Genetic Basis of Psoriasis

Psoriasis is a disease of overactive immunity in genetically susceptible individuals. Because patients exhibit varying skin phenotypes, extracutaneous manifestations, and disease courses, multiple genes resulting from linkage disequilibrium are believed to be involved in the pathogenesis of psoriasis. A decade of genome-wide linkage scans have established that PSORS1 is the strongest susceptibility locus demonstrable through family linkage studies; PSORS1 is responsible for up to 50% of the genetic component of psoriasis.⁶¹ More recently, HLA-Cw6 has received the most attention as a candidate gene of the PSORS1 susceptibility locus on the MHC class I region on chromosome 6p21.3.⁶² This gene may function in antigen presentation via MHC class I, which aids in the activation of the overactive T cells characteristic of psoriatic inflammation.

Studies involving the IL-23/T_H17 axis have shown genetics to play a role. Individuals may be protected from psoriasis with a nonsynonymous nucleotide substitution in the IL23R gene,^47-49 and certain haplotypes of the IL23R gene are associated with the disease^47,49 in addition to other autoimmune conditions.

Genomic scans have shown additional susceptibility loci for psoriasis on chromosomes 1q21, 3q21, 4q32-35, 16q12, and 17q25. Two regions on chromosome 17q were recently localized via mapping, which demonstrated a 6 megabase pairs separation, thereby indicating independent linkage factors. Genes SLC9A3R1 and NAT9 are present in the first region, while RAPTOR is demonstrated in the second region.⁶³SLC9A3R1 and NAT9 are players that regulate signal transduction, the immunologic synapse, and T-cell growth. RAPTOR is involved in T-cell function and growth pathways. Using these genes as an example, we can predict that the alterations of regulatory genes, even those yet undetermined, can enhance T-cell proliferation and inflammation manifested in psoriasis.

Conclusion

Psoriasis is a complex disease whereby multiple exogenous and endogenous stimuli incite already heightened innate immune responses in genetically predetermined individuals. The disease process is a result of a network of cell types, including T cells, DCs, and keratinocytes that, with the production of cytokines, generate a chronic inflammatory state. Our understanding of these cellular interactions and cytokines originates from developments, some meticulously planned, others serendipitous, in the fields of immunology, cell and molecular biology, and genetics. Such progress has fostered the creation of targeted immune therapy that has demonstrated remarkable efficacy in psoriasis treatment. Further study of the underlying pathophysiology of psoriasis may provide additional targets for therapy.

This special issue is dedicated to resident education on psoriasis. With that in mind, we hope to address many topics of interest to those in training. Over the years, diet has been a hot topic among psoriasis patients. They want to know how diet affects psoriasis and what changes can be made to their diet to improve their condition. Although they have expected specific answers, my response has usually been that they should, of course, eat an overall healthy and balanced diet, and lose weight if necessary. I have continued, however, that no specific diet has been recommended. However, now we have some information that may start to give us some answers.

The Mediterranean diet has been regarded as a healthy regimen.¹ This diet emphasizes eating primarily plant-based foods, such as fruits and vegetables; whole grains; legumes; and nuts. Other recommendations include replacing butter with healthy fats such as olive oil and canola oil, using herbs and spices instead of salt to flavor foods, and limiting red meat to no more than a few times a month.¹

As we know, psoriasis is a chronic inflammatory disease. The Mediterranean diet has been shown to reduce chronic inflammation and has a positive effect on the risk for metabolic syndrome and cardiovascular events.¹ Phan et al¹ hypothesized a positive effect of the Mediterranean diet on psoriasis. They performed a study to assess the association between a score that reflects the adhesion to a Mediterranean diet (MEDI-LITE) and the onset and/or severity of psoriasis.¹

The NutriNet-Santé program is an ongoing, observational, web-based questionnaire cohort study launched in France in May 2009.¹ Data were collected and analyzed between April 2017 and June 2017. Individuals with psoriasis were identified utilizing a validated online questionnaire and then categorized by disease severity into 1 of 3 groups: severe psoriasis, nonsevere psoriasis, and psoriasis free.¹

During the initial 2 years of participation in the cohort, data on dietary intake (including alcohol) were gathered to calculate the MEDI-LITE score, ranging from 0 (no adherence) to 18 (maximum adherence).¹ Of the 158,361 total web-based participants, 35,735 (23%) replied to the psoriasis questionnaire.¹ Of the respondents, 3557 (10%) individuals reported having psoriasis. The condition was severe in 878 cases (24.7%), and 299 (8.4%) incident cases were recorded (cases occurring >2 years after participant inclusion in the cohort). After adjustment for confounding factors, the investigators found a significant inverse relationship between the MEDI-LITE score and having severe psoriasis (odds ratio [OR], 0.71; 95% CI, 0.55-0.92 for the MEDI-LITE score’s second tertile [score of 8 to 9]; and OR, 0.78; 95% CI, 0.59-1.01 for the third tertile [score of 10 to 18]).¹

The authors noted that patients with severe psoriasis displayed low levels of adherence to the Mediterranean diet.¹ They commented that this finding supports the hypothesis that the Mediterranean diet may slow the progression of psoriasis. If these findings are confirmed, adherence to a Mediterranean diet should be integrated into the routine management of moderate to severe psoriasis.¹ These findings are by no means definitive, but it is a first step in helping us define more specific dietary recommendations for psoriasis.

This issue includes several articles looking at various facets of psoriasis important to residents, including the pathophysiology of psoriasis,² treatment approach using biologic therapies,³ risk factors and triggers for psoriasis,⁴ and the psychosocial impact of psoriasis.⁵ We hope that you find this issue enjoyable and informative.

This special issue is dedicated to resident education on psoriasis. With that in mind, we hope to address many topics of interest to those in training. Over the years, diet has been a hot topic among psoriasis patients. They want to know how diet affects psoriasis and what changes can be made to their diet to improve their condition. Although they have expected specific answers, my response has usually been that they should, of course, eat an overall healthy and balanced diet, and lose weight if necessary. I have continued, however, that no specific diet has been recommended. However, now we have some information that may start to give us some answers.

The Mediterranean diet has been regarded as a healthy regimen.¹ This diet emphasizes eating primarily plant-based foods, such as fruits and vegetables; whole grains; legumes; and nuts. Other recommendations include replacing butter with healthy fats such as olive oil and canola oil, using herbs and spices instead of salt to flavor foods, and limiting red meat to no more than a few times a month.¹

As we know, psoriasis is a chronic inflammatory disease. The Mediterranean diet has been shown to reduce chronic inflammation and has a positive effect on the risk for metabolic syndrome and cardiovascular events.¹ Phan et al¹ hypothesized a positive effect of the Mediterranean diet on psoriasis. They performed a study to assess the association between a score that reflects the adhesion to a Mediterranean diet (MEDI-LITE) and the onset and/or severity of psoriasis.¹

The NutriNet-Santé program is an ongoing, observational, web-based questionnaire cohort study launched in France in May 2009.¹ Data were collected and analyzed between April 2017 and June 2017. Individuals with psoriasis were identified utilizing a validated online questionnaire and then categorized by disease severity into 1 of 3 groups: severe psoriasis, nonsevere psoriasis, and psoriasis free.¹

During the initial 2 years of participation in the cohort, data on dietary intake (including alcohol) were gathered to calculate the MEDI-LITE score, ranging from 0 (no adherence) to 18 (maximum adherence).¹ Of the 158,361 total web-based participants, 35,735 (23%) replied to the psoriasis questionnaire.¹ Of the respondents, 3557 (10%) individuals reported having psoriasis. The condition was severe in 878 cases (24.7%), and 299 (8.4%) incident cases were recorded (cases occurring >2 years after participant inclusion in the cohort). After adjustment for confounding factors, the investigators found a significant inverse relationship between the MEDI-LITE score and having severe psoriasis (odds ratio [OR], 0.71; 95% CI, 0.55-0.92 for the MEDI-LITE score’s second tertile [score of 8 to 9]; and OR, 0.78; 95% CI, 0.59-1.01 for the third tertile [score of 10 to 18]).¹

The authors noted that patients with severe psoriasis displayed low levels of adherence to the Mediterranean diet.¹ They commented that this finding supports the hypothesis that the Mediterranean diet may slow the progression of psoriasis. If these findings are confirmed, adherence to a Mediterranean diet should be integrated into the routine management of moderate to severe psoriasis.¹ These findings are by no means definitive, but it is a first step in helping us define more specific dietary recommendations for psoriasis.

This issue includes several articles looking at various facets of psoriasis important to residents, including the pathophysiology of psoriasis,² treatment approach using biologic therapies,³ risk factors and triggers for psoriasis,⁴ and the psychosocial impact of psoriasis.⁵ We hope that you find this issue enjoyable and informative.

This special issue is dedicated to resident education on psoriasis. With that in mind, we hope to address many topics of interest to those in training. Over the years, diet has been a hot topic among psoriasis patients. They want to know how diet affects psoriasis and what changes can be made to their diet to improve their condition. Although they have expected specific answers, my response has usually been that they should, of course, eat an overall healthy and balanced diet, and lose weight if necessary. I have continued, however, that no specific diet has been recommended. However, now we have some information that may start to give us some answers.

The Mediterranean diet has been regarded as a healthy regimen.¹ This diet emphasizes eating primarily plant-based foods, such as fruits and vegetables; whole grains; legumes; and nuts. Other recommendations include replacing butter with healthy fats such as olive oil and canola oil, using herbs and spices instead of salt to flavor foods, and limiting red meat to no more than a few times a month.¹

As we know, psoriasis is a chronic inflammatory disease. The Mediterranean diet has been shown to reduce chronic inflammation and has a positive effect on the risk for metabolic syndrome and cardiovascular events.¹ Phan et al¹ hypothesized a positive effect of the Mediterranean diet on psoriasis. They performed a study to assess the association between a score that reflects the adhesion to a Mediterranean diet (MEDI-LITE) and the onset and/or severity of psoriasis.¹

The NutriNet-Santé program is an ongoing, observational, web-based questionnaire cohort study launched in France in May 2009.¹ Data were collected and analyzed between April 2017 and June 2017. Individuals with psoriasis were identified utilizing a validated online questionnaire and then categorized by disease severity into 1 of 3 groups: severe psoriasis, nonsevere psoriasis, and psoriasis free.¹

During the initial 2 years of participation in the cohort, data on dietary intake (including alcohol) were gathered to calculate the MEDI-LITE score, ranging from 0 (no adherence) to 18 (maximum adherence).¹ Of the 158,361 total web-based participants, 35,735 (23%) replied to the psoriasis questionnaire.¹ Of the respondents, 3557 (10%) individuals reported having psoriasis. The condition was severe in 878 cases (24.7%), and 299 (8.4%) incident cases were recorded (cases occurring >2 years after participant inclusion in the cohort). After adjustment for confounding factors, the investigators found a significant inverse relationship between the MEDI-LITE score and having severe psoriasis (odds ratio [OR], 0.71; 95% CI, 0.55-0.92 for the MEDI-LITE score’s second tertile [score of 8 to 9]; and OR, 0.78; 95% CI, 0.59-1.01 for the third tertile [score of 10 to 18]).¹

The authors noted that patients with severe psoriasis displayed low levels of adherence to the Mediterranean diet.¹ They commented that this finding supports the hypothesis that the Mediterranean diet may slow the progression of psoriasis. If these findings are confirmed, adherence to a Mediterranean diet should be integrated into the routine management of moderate to severe psoriasis.¹ These findings are by no means definitive, but it is a first step in helping us define more specific dietary recommendations for psoriasis.

This issue includes several articles looking at various facets of psoriasis important to residents, including the pathophysiology of psoriasis,² treatment approach using biologic therapies,³ risk factors and triggers for psoriasis,⁴ and the psychosocial impact of psoriasis.⁵ We hope that you find this issue enjoyable and informative.

The Diagnosis: Pediculosis Pubis

Dermoscopy of the pubic hair demonstrated a louse clutching multiple shafts of hairs (Figure) as well as scattered nits, confirming the presence of Phthirus pubis and diagnosis of pediculosis pubis. The key clinical diagnostic feature in this case was severe itching of the pubic area, with visible nits present on pubic hairs. Itching and infestation also can involve other hair-bearing areas such as the chest, legs, and axillae. The patient was treated with permethrin cream 5% applied to the pubic area and chest. Symptoms and infestation were resolved at 1-week follow-up.

Pediculosis pubis is an infestation of pubic hairs by the pubic (crab) louse P pubis, which feeds on host blood. Other body areas covered with dense hair also may be involved; 60% of patients are infested in at least 2 different sites.¹ Pediculosis pubis is most commonly sexually transmitted through direct contact.² Worldwide prevalence has been estimated at approximately 2% of the adult population, and a survey of 817 US college students in 2009 indicated a lifetime prevalence of 1.3%.³ The prevalence is slightly higher in men, highest in men who have sex with men, and rare in individuals with shaved pubic hair.¹ The most common symptom is pruritus of the genital area. Infested patients also may develop asymptomatic bluish gray macules (maculae ceruleae) secondary to hemosiderin deposition from louse bites.⁴

The diagnosis of pediculosis pubis is made by identification of P pubis, either by examination with the naked eye or confirmation with dermoscopy or microscopy. Although the 0.8- to 1.2-mm lice are visible to the naked eye, they can be difficult to see if not filled with blood, and nits on the hairs can be mistaken for white piedra (fungal infection of the hair shafts) or trichomycosis pubis (bacterial infection of the hair shafts).⁴ Scabies and tinea cruris do not present with attachments to the hairs. Scabies may present with papules and burrows and tinea cruris with scaly erythematous plaques. Small numbers of lice and nits may be missed by the naked eye or a traditional magnifying glass.⁵ The use of dermoscopy allows for fast and accurate identification of the characteristic lice and nits, even in these more challenging cases.⁵ Accurate diagnosis is important, as approximately 31% of infested patients have other concurrent sexually transmitted infections that warrant screening.⁶

The Centers for Disease Control and Prevention recommends first-line treatment with permethrin cream (1% or 5%) or pyrethrin with piperonyl butoxide applied to all affected areas and washed off after 10 minutes.⁷ Patients should be reevaluated after 1 week if symptoms persist and re-treated if lice are found on examination.^7,8 Malathion lotion 0.5% (applied and washed off after 8-12 hours) or oral ivermectin (250 µg/kg, repeated after 2 weeks) may be used for alternative therapies or cases of permethrin or pyrethrin resistance.⁷ Ivermectin also is effective for involvement of eyelashes where topical insecticides should not be used.⁹ Sexual partners should be treated to prevent repeat transmission.^7,8 Bedding and clothing can be decontaminated by machine wash on hot cycle or isolating from body contact for 72 hours.⁷ Patients also should be screened for other sexually transmitted infections, including human immunodeficiency virus.⁶

The Diagnosis: Pediculosis Pubis

Dermoscopy of the pubic hair demonstrated a louse clutching multiple shafts of hairs (Figure) as well as scattered nits, confirming the presence of Phthirus pubis and diagnosis of pediculosis pubis. The key clinical diagnostic feature in this case was severe itching of the pubic area, with visible nits present on pubic hairs. Itching and infestation also can involve other hair-bearing areas such as the chest, legs, and axillae. The patient was treated with permethrin cream 5% applied to the pubic area and chest. Symptoms and infestation were resolved at 1-week follow-up.

Pediculosis pubis is an infestation of pubic hairs by the pubic (crab) louse P pubis, which feeds on host blood. Other body areas covered with dense hair also may be involved; 60% of patients are infested in at least 2 different sites.¹ Pediculosis pubis is most commonly sexually transmitted through direct contact.² Worldwide prevalence has been estimated at approximately 2% of the adult population, and a survey of 817 US college students in 2009 indicated a lifetime prevalence of 1.3%.³ The prevalence is slightly higher in men, highest in men who have sex with men, and rare in individuals with shaved pubic hair.¹ The most common symptom is pruritus of the genital area. Infested patients also may develop asymptomatic bluish gray macules (maculae ceruleae) secondary to hemosiderin deposition from louse bites.⁴

The diagnosis of pediculosis pubis is made by identification of P pubis, either by examination with the naked eye or confirmation with dermoscopy or microscopy. Although the 0.8- to 1.2-mm lice are visible to the naked eye, they can be difficult to see if not filled with blood, and nits on the hairs can be mistaken for white piedra (fungal infection of the hair shafts) or trichomycosis pubis (bacterial infection of the hair shafts).⁴ Scabies and tinea cruris do not present with attachments to the hairs. Scabies may present with papules and burrows and tinea cruris with scaly erythematous plaques. Small numbers of lice and nits may be missed by the naked eye or a traditional magnifying glass.⁵ The use of dermoscopy allows for fast and accurate identification of the characteristic lice and nits, even in these more challenging cases.⁵ Accurate diagnosis is important, as approximately 31% of infested patients have other concurrent sexually transmitted infections that warrant screening.⁶

The Centers for Disease Control and Prevention recommends first-line treatment with permethrin cream (1% or 5%) or pyrethrin with piperonyl butoxide applied to all affected areas and washed off after 10 minutes.⁷ Patients should be reevaluated after 1 week if symptoms persist and re-treated if lice are found on examination.^7,8 Malathion lotion 0.5% (applied and washed off after 8-12 hours) or oral ivermectin (250 µg/kg, repeated after 2 weeks) may be used for alternative therapies or cases of permethrin or pyrethrin resistance.⁷ Ivermectin also is effective for involvement of eyelashes where topical insecticides should not be used.⁹ Sexual partners should be treated to prevent repeat transmission.^7,8 Bedding and clothing can be decontaminated by machine wash on hot cycle or isolating from body contact for 72 hours.⁷ Patients also should be screened for other sexually transmitted infections, including human immunodeficiency virus.⁶

The Diagnosis: Pediculosis Pubis

Dermoscopy of the pubic hair demonstrated a louse clutching multiple shafts of hairs (Figure) as well as scattered nits, confirming the presence of Phthirus pubis and diagnosis of pediculosis pubis. The key clinical diagnostic feature in this case was severe itching of the pubic area, with visible nits present on pubic hairs. Itching and infestation also can involve other hair-bearing areas such as the chest, legs, and axillae. The patient was treated with permethrin cream 5% applied to the pubic area and chest. Symptoms and infestation were resolved at 1-week follow-up.

Pediculosis pubis is an infestation of pubic hairs by the pubic (crab) louse P pubis, which feeds on host blood. Other body areas covered with dense hair also may be involved; 60% of patients are infested in at least 2 different sites.¹ Pediculosis pubis is most commonly sexually transmitted through direct contact.² Worldwide prevalence has been estimated at approximately 2% of the adult population, and a survey of 817 US college students in 2009 indicated a lifetime prevalence of 1.3%.³ The prevalence is slightly higher in men, highest in men who have sex with men, and rare in individuals with shaved pubic hair.¹ The most common symptom is pruritus of the genital area. Infested patients also may develop asymptomatic bluish gray macules (maculae ceruleae) secondary to hemosiderin deposition from louse bites.⁴

The diagnosis of pediculosis pubis is made by identification of P pubis, either by examination with the naked eye or confirmation with dermoscopy or microscopy. Although the 0.8- to 1.2-mm lice are visible to the naked eye, they can be difficult to see if not filled with blood, and nits on the hairs can be mistaken for white piedra (fungal infection of the hair shafts) or trichomycosis pubis (bacterial infection of the hair shafts).⁴ Scabies and tinea cruris do not present with attachments to the hairs. Scabies may present with papules and burrows and tinea cruris with scaly erythematous plaques. Small numbers of lice and nits may be missed by the naked eye or a traditional magnifying glass.⁵ The use of dermoscopy allows for fast and accurate identification of the characteristic lice and nits, even in these more challenging cases.⁵ Accurate diagnosis is important, as approximately 31% of infested patients have other concurrent sexually transmitted infections that warrant screening.⁶

The Centers for Disease Control and Prevention recommends first-line treatment with permethrin cream (1% or 5%) or pyrethrin with piperonyl butoxide applied to all affected areas and washed off after 10 minutes.⁷ Patients should be reevaluated after 1 week if symptoms persist and re-treated if lice are found on examination.^7,8 Malathion lotion 0.5% (applied and washed off after 8-12 hours) or oral ivermectin (250 µg/kg, repeated after 2 weeks) may be used for alternative therapies or cases of permethrin or pyrethrin resistance.⁷ Ivermectin also is effective for involvement of eyelashes where topical insecticides should not be used.⁹ Sexual partners should be treated to prevent repeat transmission.^7,8 Bedding and clothing can be decontaminated by machine wash on hot cycle or isolating from body contact for 72 hours.⁷ Patients also should be screened for other sexually transmitted infections, including human immunodeficiency virus.⁶

Cross-contamination of pathology specimens is a rare but nonnegligible source of potential morbidity in clinical practice. Contaminant tissue fragments, colloquially referred to as floaters, typically are readily identifiable based on obvious cytomorphologic differences, especially if the tissues arise from different organs; however, one cannot rely on such distinctions in a pathology laboratory dedicated to a single organ system (eg, dermatopathology). The inability to identify quickly and confidently the presence of a contaminant puts the patient at risk for misdiagnosis, which can lead to unnecessary morbidity or even mortality in the case of cancer misdiagnosis. Studies that have been conducted to estimate the incidence of this type of error have suggested an overall incidence rate between approximately 1% and 3%.^1,2 Awareness of this phenomenon and careful scrutiny when the histopathologic evidence diverges considerably from the clinical impression is critical for minimizing the negative outcomes that could result from the presence of contaminant tissue. We present a case in which cross-contamination of a pathology specimen led to an initial erroneous diagnosis of an aggressive cutaneous melanoma in a patient with a benign adnexal neoplasm.

Case Report

A 72-year-old man was referred to the Pigmented Lesion and Melanoma Program at Stanford University Medical Center and Cancer Institute (Palo Alto, California) for evaluation and treatment of a presumed stage IIB melanoma on the right preauricular cheek based on a shave biopsy that had been performed (<1 month prior) by his local dermatology provider and subsequently read by an affiliated out-of-state dermatopathology laboratory. Per the clinical history that was gathered at the current presentation, neither the patient nor his wife had noticed the lesion prior to his dermatology provider pointing it out on the day of the biopsy. Additionally, he denied associated pain, bleeding, or ulceration. According to outside medical records, the referring dermatology provider described the lesion as a 4-mm pink pearly papule with telangiectasia favoring a diagnosis of basal cell carcinoma, and a diagnostic shave biopsy was performed. On presentation to our clinic, physical examination of the right preauricular cheek revealed a 4×3-mm depressed erythematous scar with no evidence of residual pigmentation or nodularity (Figure 1). There was no clinically appreciable regional lymphadenopathy.

The original dermatopathology report indicated an invasive melanoma with the following pathologic characteristics: superficial spreading type, Breslow depth of at least 2.16 mm, ulceration, and a mitotic index of 8 mitotic figures/mm² with transection of the invasive component at the peripheral and deep margins. There was no evidence of regression, perineural invasion, lymphovascular invasion, or microsatellites. Interestingly, the report indicated that there also was a basaloid proliferation with features of cylindroma in the same pathology slide adjacent to the aggressive invasive melanoma that was described. Given the complexity of cases referred to our academic center, the standard of care includes internal dermatopathology review of all outside pathology specimens. This review proved critical to this patient’s care in light of the considerable divergence of the initial pathologic diagnosis and the reported clinical features of the lesion.

Internal review of the single pathology slide received from the referring provider showed a total of 4 sections, 3 of which are shown here (Figure 2A). Three sections, including the one not shown, were all consistent with a diagnosis of cylindroma and showed no evidence of a melanocytic proliferation (Figure 2B). However, the fourth section demonstrated marked morphologic dissimilarity compared to the other 3 sections. This outlier section showed a thick cutaneous melanoma with a Breslow depth of at least 2.1 mm, ulceration, a mitotic rate of 12 mitotic figures/mm², and broad transection of the invasive component at the peripheral and deep margins (Figures 2C and 2D). Correlation with the gross description of tissue processing on the original pathology report indicating that the specimen had been trisected raised suspicion that the fourth and very dissimilar section could be a contaminant from another source that was incorporated into our patient’s histologic sections during processing. Taken together, these discrepancies made the diagnosis of cylindroma alone far more likely than cutaneous melanoma, but we needed conclusive evidence given the dramatic difference in prognosis and management between a cylindroma and an aggressive cutaneous melanoma.

For further diagnostic clarification, we performed polymorphic short tandem repeat (STR) analysis, a well-described forensic pathology technique, to determine if the melanoma and cylindroma specimens derived from different patients, as we hypothesized. This analysis revealed differences in all but one DNA locus tested between the cylindroma specimen and the melanoma specimen, confirming our hypothesis (Figure 3). Subsequent discussion of the case with staff from the dermatopathology laboratory that processed this specimen provided further support for our suspicion that the invasive melanoma specimen was part of a case processed prior to our patient’s benign lesion. Therefore, the wide local excision for treatment of the suspected melanoma fortunately was canceled, and the patient did not require further treatment of the benign cylindroma. The patient expressed relief and gratitude for this critical clarification and change in management.

Comment

Shah et al³ reported a similar case in which a benign granuloma of the lung masqueraded as a squamous cell carcinoma due to histopathologic contamination. Although few similar cases have been described in the literature, the risk posed by such contamination is remarkable, regardless of whether it occurs during specimen grossing, embedding, sectioning, or staining.^1,4,5 This risk is amplified in facilities that process specimens originating predominantly from a single organ system or tissue type, as is often the case in dedicated dermatopathology laboratories. In this scenario, it is unlikely that one could use the presence of tissues from 2 different organ systems on a single slide as a way of easily recognizing the presence of a contaminant and rectifying the error. Additionally, the presence of malignant cells in the contaminant further complicates the problem and requires an investigation that can conclusively distinguish the contaminant from the patient’s actual tissue.

In our case, our dermatology and dermatopathology teams partnered with our molecular pathology team to find a solution. Polymorphic STR analysis via polymerase chain reaction amplification is a sensitive method employed commonly in forensic DNA laboratories for determining whether a sample submitted as evidence belongs to a given suspect.⁶ Although much more commonly used in forensics, STR analysis does have known roles in clinical medicine, such as chimerism testing after bone marrow or allogeneic stem cell transplantation.⁷ Given the relatively short period of time it takes along with the convenience of commercially available kits, a high discriminative ability, and well-validated interpretation procedures, STR analysis is an excellent method for determining if a given tissue sample came from a given patient, which is what was needed in our case.

The combined clinical, histopathologic, and molecular data in our case allowed for confident clarification of our patient’s diagnosis, sparing him the morbidity of wide local excision on the face, sentinel lymph node biopsy, and emotional distress associated with a diagnosis of aggressive cutaneous melanoma. Our case highlights the critical importance of internal review of pathology specimens in ensuring proper diagnosis and management and reminds us that, though rare, accidental contamination during processing of pathology specimens is a potential adverse event that must be considered, especially when a pathologic finding diverges considerably from what is anticipated based on the patient’s history and physical examination.

Acknowledgment
The authors express gratitude to the patient described herein who graciously provided permission for us to publish his case and clinical photography.

Cross-contamination of pathology specimens is a rare but nonnegligible source of potential morbidity in clinical practice. Contaminant tissue fragments, colloquially referred to as floaters, typically are readily identifiable based on obvious cytomorphologic differences, especially if the tissues arise from different organs; however, one cannot rely on such distinctions in a pathology laboratory dedicated to a single organ system (eg, dermatopathology). The inability to identify quickly and confidently the presence of a contaminant puts the patient at risk for misdiagnosis, which can lead to unnecessary morbidity or even mortality in the case of cancer misdiagnosis. Studies that have been conducted to estimate the incidence of this type of error have suggested an overall incidence rate between approximately 1% and 3%.^1,2 Awareness of this phenomenon and careful scrutiny when the histopathologic evidence diverges considerably from the clinical impression is critical for minimizing the negative outcomes that could result from the presence of contaminant tissue. We present a case in which cross-contamination of a pathology specimen led to an initial erroneous diagnosis of an aggressive cutaneous melanoma in a patient with a benign adnexal neoplasm.

Case Report

A 72-year-old man was referred to the Pigmented Lesion and Melanoma Program at Stanford University Medical Center and Cancer Institute (Palo Alto, California) for evaluation and treatment of a presumed stage IIB melanoma on the right preauricular cheek based on a shave biopsy that had been performed (<1 month prior) by his local dermatology provider and subsequently read by an affiliated out-of-state dermatopathology laboratory. Per the clinical history that was gathered at the current presentation, neither the patient nor his wife had noticed the lesion prior to his dermatology provider pointing it out on the day of the biopsy. Additionally, he denied associated pain, bleeding, or ulceration. According to outside medical records, the referring dermatology provider described the lesion as a 4-mm pink pearly papule with telangiectasia favoring a diagnosis of basal cell carcinoma, and a diagnostic shave biopsy was performed. On presentation to our clinic, physical examination of the right preauricular cheek revealed a 4×3-mm depressed erythematous scar with no evidence of residual pigmentation or nodularity (Figure 1). There was no clinically appreciable regional lymphadenopathy.

The original dermatopathology report indicated an invasive melanoma with the following pathologic characteristics: superficial spreading type, Breslow depth of at least 2.16 mm, ulceration, and a mitotic index of 8 mitotic figures/mm² with transection of the invasive component at the peripheral and deep margins. There was no evidence of regression, perineural invasion, lymphovascular invasion, or microsatellites. Interestingly, the report indicated that there also was a basaloid proliferation with features of cylindroma in the same pathology slide adjacent to the aggressive invasive melanoma that was described. Given the complexity of cases referred to our academic center, the standard of care includes internal dermatopathology review of all outside pathology specimens. This review proved critical to this patient’s care in light of the considerable divergence of the initial pathologic diagnosis and the reported clinical features of the lesion.

Internal review of the single pathology slide received from the referring provider showed a total of 4 sections, 3 of which are shown here (Figure 2A). Three sections, including the one not shown, were all consistent with a diagnosis of cylindroma and showed no evidence of a melanocytic proliferation (Figure 2B). However, the fourth section demonstrated marked morphologic dissimilarity compared to the other 3 sections. This outlier section showed a thick cutaneous melanoma with a Breslow depth of at least 2.1 mm, ulceration, a mitotic rate of 12 mitotic figures/mm², and broad transection of the invasive component at the peripheral and deep margins (Figures 2C and 2D). Correlation with the gross description of tissue processing on the original pathology report indicating that the specimen had been trisected raised suspicion that the fourth and very dissimilar section could be a contaminant from another source that was incorporated into our patient’s histologic sections during processing. Taken together, these discrepancies made the diagnosis of cylindroma alone far more likely than cutaneous melanoma, but we needed conclusive evidence given the dramatic difference in prognosis and management between a cylindroma and an aggressive cutaneous melanoma.

For further diagnostic clarification, we performed polymorphic short tandem repeat (STR) analysis, a well-described forensic pathology technique, to determine if the melanoma and cylindroma specimens derived from different patients, as we hypothesized. This analysis revealed differences in all but one DNA locus tested between the cylindroma specimen and the melanoma specimen, confirming our hypothesis (Figure 3). Subsequent discussion of the case with staff from the dermatopathology laboratory that processed this specimen provided further support for our suspicion that the invasive melanoma specimen was part of a case processed prior to our patient’s benign lesion. Therefore, the wide local excision for treatment of the suspected melanoma fortunately was canceled, and the patient did not require further treatment of the benign cylindroma. The patient expressed relief and gratitude for this critical clarification and change in management.

Comment

Shah et al³ reported a similar case in which a benign granuloma of the lung masqueraded as a squamous cell carcinoma due to histopathologic contamination. Although few similar cases have been described in the literature, the risk posed by such contamination is remarkable, regardless of whether it occurs during specimen grossing, embedding, sectioning, or staining.^1,4,5 This risk is amplified in facilities that process specimens originating predominantly from a single organ system or tissue type, as is often the case in dedicated dermatopathology laboratories. In this scenario, it is unlikely that one could use the presence of tissues from 2 different organ systems on a single slide as a way of easily recognizing the presence of a contaminant and rectifying the error. Additionally, the presence of malignant cells in the contaminant further complicates the problem and requires an investigation that can conclusively distinguish the contaminant from the patient’s actual tissue.

In our case, our dermatology and dermatopathology teams partnered with our molecular pathology team to find a solution. Polymorphic STR analysis via polymerase chain reaction amplification is a sensitive method employed commonly in forensic DNA laboratories for determining whether a sample submitted as evidence belongs to a given suspect.⁶ Although much more commonly used in forensics, STR analysis does have known roles in clinical medicine, such as chimerism testing after bone marrow or allogeneic stem cell transplantation.⁷ Given the relatively short period of time it takes along with the convenience of commercially available kits, a high discriminative ability, and well-validated interpretation procedures, STR analysis is an excellent method for determining if a given tissue sample came from a given patient, which is what was needed in our case.

The combined clinical, histopathologic, and molecular data in our case allowed for confident clarification of our patient’s diagnosis, sparing him the morbidity of wide local excision on the face, sentinel lymph node biopsy, and emotional distress associated with a diagnosis of aggressive cutaneous melanoma. Our case highlights the critical importance of internal review of pathology specimens in ensuring proper diagnosis and management and reminds us that, though rare, accidental contamination during processing of pathology specimens is a potential adverse event that must be considered, especially when a pathologic finding diverges considerably from what is anticipated based on the patient’s history and physical examination.

Acknowledgment
The authors express gratitude to the patient described herein who graciously provided permission for us to publish his case and clinical photography.

Cross-contamination of pathology specimens is a rare but nonnegligible source of potential morbidity in clinical practice. Contaminant tissue fragments, colloquially referred to as floaters, typically are readily identifiable based on obvious cytomorphologic differences, especially if the tissues arise from different organs; however, one cannot rely on such distinctions in a pathology laboratory dedicated to a single organ system (eg, dermatopathology). The inability to identify quickly and confidently the presence of a contaminant puts the patient at risk for misdiagnosis, which can lead to unnecessary morbidity or even mortality in the case of cancer misdiagnosis. Studies that have been conducted to estimate the incidence of this type of error have suggested an overall incidence rate between approximately 1% and 3%.^1,2 Awareness of this phenomenon and careful scrutiny when the histopathologic evidence diverges considerably from the clinical impression is critical for minimizing the negative outcomes that could result from the presence of contaminant tissue. We present a case in which cross-contamination of a pathology specimen led to an initial erroneous diagnosis of an aggressive cutaneous melanoma in a patient with a benign adnexal neoplasm.

Case Report

A 72-year-old man was referred to the Pigmented Lesion and Melanoma Program at Stanford University Medical Center and Cancer Institute (Palo Alto, California) for evaluation and treatment of a presumed stage IIB melanoma on the right preauricular cheek based on a shave biopsy that had been performed (<1 month prior) by his local dermatology provider and subsequently read by an affiliated out-of-state dermatopathology laboratory. Per the clinical history that was gathered at the current presentation, neither the patient nor his wife had noticed the lesion prior to his dermatology provider pointing it out on the day of the biopsy. Additionally, he denied associated pain, bleeding, or ulceration. According to outside medical records, the referring dermatology provider described the lesion as a 4-mm pink pearly papule with telangiectasia favoring a diagnosis of basal cell carcinoma, and a diagnostic shave biopsy was performed. On presentation to our clinic, physical examination of the right preauricular cheek revealed a 4×3-mm depressed erythematous scar with no evidence of residual pigmentation or nodularity (Figure 1). There was no clinically appreciable regional lymphadenopathy.

The original dermatopathology report indicated an invasive melanoma with the following pathologic characteristics: superficial spreading type, Breslow depth of at least 2.16 mm, ulceration, and a mitotic index of 8 mitotic figures/mm² with transection of the invasive component at the peripheral and deep margins. There was no evidence of regression, perineural invasion, lymphovascular invasion, or microsatellites. Interestingly, the report indicated that there also was a basaloid proliferation with features of cylindroma in the same pathology slide adjacent to the aggressive invasive melanoma that was described. Given the complexity of cases referred to our academic center, the standard of care includes internal dermatopathology review of all outside pathology specimens. This review proved critical to this patient’s care in light of the considerable divergence of the initial pathologic diagnosis and the reported clinical features of the lesion.

Internal review of the single pathology slide received from the referring provider showed a total of 4 sections, 3 of which are shown here (Figure 2A). Three sections, including the one not shown, were all consistent with a diagnosis of cylindroma and showed no evidence of a melanocytic proliferation (Figure 2B). However, the fourth section demonstrated marked morphologic dissimilarity compared to the other 3 sections. This outlier section showed a thick cutaneous melanoma with a Breslow depth of at least 2.1 mm, ulceration, a mitotic rate of 12 mitotic figures/mm², and broad transection of the invasive component at the peripheral and deep margins (Figures 2C and 2D). Correlation with the gross description of tissue processing on the original pathology report indicating that the specimen had been trisected raised suspicion that the fourth and very dissimilar section could be a contaminant from another source that was incorporated into our patient’s histologic sections during processing. Taken together, these discrepancies made the diagnosis of cylindroma alone far more likely than cutaneous melanoma, but we needed conclusive evidence given the dramatic difference in prognosis and management between a cylindroma and an aggressive cutaneous melanoma.

For further diagnostic clarification, we performed polymorphic short tandem repeat (STR) analysis, a well-described forensic pathology technique, to determine if the melanoma and cylindroma specimens derived from different patients, as we hypothesized. This analysis revealed differences in all but one DNA locus tested between the cylindroma specimen and the melanoma specimen, confirming our hypothesis (Figure 3). Subsequent discussion of the case with staff from the dermatopathology laboratory that processed this specimen provided further support for our suspicion that the invasive melanoma specimen was part of a case processed prior to our patient’s benign lesion. Therefore, the wide local excision for treatment of the suspected melanoma fortunately was canceled, and the patient did not require further treatment of the benign cylindroma. The patient expressed relief and gratitude for this critical clarification and change in management.

Comment

Shah et al³ reported a similar case in which a benign granuloma of the lung masqueraded as a squamous cell carcinoma due to histopathologic contamination. Although few similar cases have been described in the literature, the risk posed by such contamination is remarkable, regardless of whether it occurs during specimen grossing, embedding, sectioning, or staining.^1,4,5 This risk is amplified in facilities that process specimens originating predominantly from a single organ system or tissue type, as is often the case in dedicated dermatopathology laboratories. In this scenario, it is unlikely that one could use the presence of tissues from 2 different organ systems on a single slide as a way of easily recognizing the presence of a contaminant and rectifying the error. Additionally, the presence of malignant cells in the contaminant further complicates the problem and requires an investigation that can conclusively distinguish the contaminant from the patient’s actual tissue.

In our case, our dermatology and dermatopathology teams partnered with our molecular pathology team to find a solution. Polymorphic STR analysis via polymerase chain reaction amplification is a sensitive method employed commonly in forensic DNA laboratories for determining whether a sample submitted as evidence belongs to a given suspect.⁶ Although much more commonly used in forensics, STR analysis does have known roles in clinical medicine, such as chimerism testing after bone marrow or allogeneic stem cell transplantation.⁷ Given the relatively short period of time it takes along with the convenience of commercially available kits, a high discriminative ability, and well-validated interpretation procedures, STR analysis is an excellent method for determining if a given tissue sample came from a given patient, which is what was needed in our case.

The combined clinical, histopathologic, and molecular data in our case allowed for confident clarification of our patient’s diagnosis, sparing him the morbidity of wide local excision on the face, sentinel lymph node biopsy, and emotional distress associated with a diagnosis of aggressive cutaneous melanoma. Our case highlights the critical importance of internal review of pathology specimens in ensuring proper diagnosis and management and reminds us that, though rare, accidental contamination during processing of pathology specimens is a potential adverse event that must be considered, especially when a pathologic finding diverges considerably from what is anticipated based on the patient’s history and physical examination.

Acknowledgment
The authors express gratitude to the patient described herein who graciously provided permission for us to publish his case and clinical photography.

The Diagnosis: Pemphigus Vegetans

A punch biopsy was taken from the verrucous plaque, and microscopic examination demonstrated prominent epidermal hyperplasia with intraepidermal eosinophilic microabscesses and a superficial dermatitis with abundant eosinophils (Figure 1A). Suprabasal acantholytic cleft formation was noted in a focal area (Figure 1B). Another punch biopsy was performed from the perilesional skin for direct immunofluorescence examination, which revealed intercellular deposits of IgG and C3 throughout the lower half of the epidermis (Figure 1C). Indirect immunofluorescence performed on monkey esophagus substrate showed circulating intercellular IgG antibodies in all the titers of up to 1/160 and an elevated level of IgG antidesmoglein 3 (anti-Dsg3) antibody (enzyme-linked immunosorbent assay index value, >200 RU/mL [reference range, <20 RU/mL]).

Because there was a solitary lesion, the decision was made to perform local treatment. One intralesional triamcinolone acetonide injection (20 mg/mL) resulted in remarkable flattening of the lesion (Figure 2). Subsequently, treatment was continued with clobetasol propionate ointment 3 times weekly for 1 month. During a follow-up period of 2 years, no signs of local relapse or new lesions elsewhere were noted, and the patient continued to be on long-term longitudinal evaluation.

Pemphigus vegetans (PV) is an uncommon variant of pemphigus, typically manifesting with vegetating erosions and plaques localized to the intertriginous areas of the body. Local factors such as semiocclusion, maceration, and/or bacterial or fungal colonization have been hypothesized to account for the distinctive localization and vegetation of the lesions.^1,2 Traditionally, 2 clinical subtypes of PV have been described: (1) Hallopeau type presenting with pustules that later evolve into vegetating plaques, and (2) Neumann type that initially manifests as vesicles and bullae with a more disseminated distribution, transforming into hypertrophic masses with erosions.^1-5 However, this distinction may not always be clear, and patients with features of both forms have been reported.^2,5

At present, our case would best be regarded as a localized form of PV presenting with a solitary lesion. It may progress to more disseminated disease or remain localized during its course; the literature contains reports exemplifying both possibilities. In a large retrospective study from Tunisia encompassing almost 3 decades, the majority of the patients initially presented with unifocal involvement; however, the disease eventually became multifocal in almost all patients during the study period, emphasizing the need for long-term follow-up.² There also are reports of PV confined to a single anatomic site, such as the scalp, sole, or vulva, that remained localized for years.^2,4,6,7 Involvement of the oral mucosa is an important finding of PV and the presenting concern in approximately three-quarters of patients.² Interestingly, the oral mucosa was not involved in our patient despite the high titer of anti-Dsg3 antibody, which suggests the need for the presence of other factors for clinical expression of the disease.

Although PV is considered a vegetating clinicomorphologic variant of pemphigus vulgaris, PV is histopathologically distinguished from pemphigus vulgaris by the presence of epidermal hyperplasia and intraepidermal eosinophilic microabscesses. Importantly, the epidermis displays signs of exuberant proliferation such as pseudoepitheliomatous hyperplasia and/or papillomatosis of a varying degree.^1,2,5 Of note, suprabasal acantholysis is usually overshadowed by the changes in PV and presents only focally, as in our patient. The most common autoantibody profile is IgG targeting Dsg3; however, a spectrum of other autoantibodies has been identified, such as IgG antidesmocollin 3, IgA anti-Dsg3, and IgG anti-Dsg1.^8,9

The most important differential diagnosis of PV is pyodermatitis-pyostomatitis vegetans. These 2 entities share many clinical and histopathological features; however, direct immunofluorescence is helpfulfor differentiation because it generally is negative in pyodermatitis-pyostomatitis vegetans.^2,10 Furthermore, there is a well-established association between pyodermatitis-pyostomatitis vegetans and inflammatory bowel disorders, whereas PV has anecdotally been linked to malignancy, human immunodeficiency virus infection, and heroin abuse.^1,2,10 Our patient was seronegative for human immunodeficiency virus and denied weight loss or loss of appetite. For those cases of PV involving a single anatomic site, the differential diagnosis is broader and encompasses dermatoses such as verrucae, syphilitic chancre, condylomata lata, granuloma inguinale, herpes simplex virus infection, and Kaposi sarcoma.

Treatment of PV is similar to pemphigus vulgaris and consists of a combination of systemic corticosteroids and steroid-sparing agents.^1,5 On the other hand, more limited presentations of PV may be suitable for intralesional treatment with triamcinolone acetonide, thus avoiding potential adverse effects of systemic therapy.^1,2 In our case with localized involvement, a favorable response was obtained with intralesional triamcinolone acetonide, and we plan to utilize systemic corticosteroids if the disease becomes generalized during follow-up.

The Diagnosis: Pemphigus Vegetans

A punch biopsy was taken from the verrucous plaque, and microscopic examination demonstrated prominent epidermal hyperplasia with intraepidermal eosinophilic microabscesses and a superficial dermatitis with abundant eosinophils (Figure 1A). Suprabasal acantholytic cleft formation was noted in a focal area (Figure 1B). Another punch biopsy was performed from the perilesional skin for direct immunofluorescence examination, which revealed intercellular deposits of IgG and C3 throughout the lower half of the epidermis (Figure 1C). Indirect immunofluorescence performed on monkey esophagus substrate showed circulating intercellular IgG antibodies in all the titers of up to 1/160 and an elevated level of IgG antidesmoglein 3 (anti-Dsg3) antibody (enzyme-linked immunosorbent assay index value, >200 RU/mL [reference range, <20 RU/mL]).

Because there was a solitary lesion, the decision was made to perform local treatment. One intralesional triamcinolone acetonide injection (20 mg/mL) resulted in remarkable flattening of the lesion (Figure 2). Subsequently, treatment was continued with clobetasol propionate ointment 3 times weekly for 1 month. During a follow-up period of 2 years, no signs of local relapse or new lesions elsewhere were noted, and the patient continued to be on long-term longitudinal evaluation.

Pemphigus vegetans (PV) is an uncommon variant of pemphigus, typically manifesting with vegetating erosions and plaques localized to the intertriginous areas of the body. Local factors such as semiocclusion, maceration, and/or bacterial or fungal colonization have been hypothesized to account for the distinctive localization and vegetation of the lesions.^1,2 Traditionally, 2 clinical subtypes of PV have been described: (1) Hallopeau type presenting with pustules that later evolve into vegetating plaques, and (2) Neumann type that initially manifests as vesicles and bullae with a more disseminated distribution, transforming into hypertrophic masses with erosions.^1-5 However, this distinction may not always be clear, and patients with features of both forms have been reported.^2,5

At present, our case would best be regarded as a localized form of PV presenting with a solitary lesion. It may progress to more disseminated disease or remain localized during its course; the literature contains reports exemplifying both possibilities. In a large retrospective study from Tunisia encompassing almost 3 decades, the majority of the patients initially presented with unifocal involvement; however, the disease eventually became multifocal in almost all patients during the study period, emphasizing the need for long-term follow-up.² There also are reports of PV confined to a single anatomic site, such as the scalp, sole, or vulva, that remained localized for years.^2,4,6,7 Involvement of the oral mucosa is an important finding of PV and the presenting concern in approximately three-quarters of patients.² Interestingly, the oral mucosa was not involved in our patient despite the high titer of anti-Dsg3 antibody, which suggests the need for the presence of other factors for clinical expression of the disease.

Although PV is considered a vegetating clinicomorphologic variant of pemphigus vulgaris, PV is histopathologically distinguished from pemphigus vulgaris by the presence of epidermal hyperplasia and intraepidermal eosinophilic microabscesses. Importantly, the epidermis displays signs of exuberant proliferation such as pseudoepitheliomatous hyperplasia and/or papillomatosis of a varying degree.^1,2,5 Of note, suprabasal acantholysis is usually overshadowed by the changes in PV and presents only focally, as in our patient. The most common autoantibody profile is IgG targeting Dsg3; however, a spectrum of other autoantibodies has been identified, such as IgG antidesmocollin 3, IgA anti-Dsg3, and IgG anti-Dsg1.^8,9

The most important differential diagnosis of PV is pyodermatitis-pyostomatitis vegetans. These 2 entities share many clinical and histopathological features; however, direct immunofluorescence is helpfulfor differentiation because it generally is negative in pyodermatitis-pyostomatitis vegetans.^2,10 Furthermore, there is a well-established association between pyodermatitis-pyostomatitis vegetans and inflammatory bowel disorders, whereas PV has anecdotally been linked to malignancy, human immunodeficiency virus infection, and heroin abuse.^1,2,10 Our patient was seronegative for human immunodeficiency virus and denied weight loss or loss of appetite. For those cases of PV involving a single anatomic site, the differential diagnosis is broader and encompasses dermatoses such as verrucae, syphilitic chancre, condylomata lata, granuloma inguinale, herpes simplex virus infection, and Kaposi sarcoma.

Treatment of PV is similar to pemphigus vulgaris and consists of a combination of systemic corticosteroids and steroid-sparing agents.^1,5 On the other hand, more limited presentations of PV may be suitable for intralesional treatment with triamcinolone acetonide, thus avoiding potential adverse effects of systemic therapy.^1,2 In our case with localized involvement, a favorable response was obtained with intralesional triamcinolone acetonide, and we plan to utilize systemic corticosteroids if the disease becomes generalized during follow-up.

The Diagnosis: Pemphigus Vegetans

A punch biopsy was taken from the verrucous plaque, and microscopic examination demonstrated prominent epidermal hyperplasia with intraepidermal eosinophilic microabscesses and a superficial dermatitis with abundant eosinophils (Figure 1A). Suprabasal acantholytic cleft formation was noted in a focal area (Figure 1B). Another punch biopsy was performed from the perilesional skin for direct immunofluorescence examination, which revealed intercellular deposits of IgG and C3 throughout the lower half of the epidermis (Figure 1C). Indirect immunofluorescence performed on monkey esophagus substrate showed circulating intercellular IgG antibodies in all the titers of up to 1/160 and an elevated level of IgG antidesmoglein 3 (anti-Dsg3) antibody (enzyme-linked immunosorbent assay index value, >200 RU/mL [reference range, <20 RU/mL]).

Because there was a solitary lesion, the decision was made to perform local treatment. One intralesional triamcinolone acetonide injection (20 mg/mL) resulted in remarkable flattening of the lesion (Figure 2). Subsequently, treatment was continued with clobetasol propionate ointment 3 times weekly for 1 month. During a follow-up period of 2 years, no signs of local relapse or new lesions elsewhere were noted, and the patient continued to be on long-term longitudinal evaluation.

Pemphigus vegetans (PV) is an uncommon variant of pemphigus, typically manifesting with vegetating erosions and plaques localized to the intertriginous areas of the body. Local factors such as semiocclusion, maceration, and/or bacterial or fungal colonization have been hypothesized to account for the distinctive localization and vegetation of the lesions.^1,2 Traditionally, 2 clinical subtypes of PV have been described: (1) Hallopeau type presenting with pustules that later evolve into vegetating plaques, and (2) Neumann type that initially manifests as vesicles and bullae with a more disseminated distribution, transforming into hypertrophic masses with erosions.^1-5 However, this distinction may not always be clear, and patients with features of both forms have been reported.^2,5

At present, our case would best be regarded as a localized form of PV presenting with a solitary lesion. It may progress to more disseminated disease or remain localized during its course; the literature contains reports exemplifying both possibilities. In a large retrospective study from Tunisia encompassing almost 3 decades, the majority of the patients initially presented with unifocal involvement; however, the disease eventually became multifocal in almost all patients during the study period, emphasizing the need for long-term follow-up.² There also are reports of PV confined to a single anatomic site, such as the scalp, sole, or vulva, that remained localized for years.^2,4,6,7 Involvement of the oral mucosa is an important finding of PV and the presenting concern in approximately three-quarters of patients.² Interestingly, the oral mucosa was not involved in our patient despite the high titer of anti-Dsg3 antibody, which suggests the need for the presence of other factors for clinical expression of the disease.

Although PV is considered a vegetating clinicomorphologic variant of pemphigus vulgaris, PV is histopathologically distinguished from pemphigus vulgaris by the presence of epidermal hyperplasia and intraepidermal eosinophilic microabscesses. Importantly, the epidermis displays signs of exuberant proliferation such as pseudoepitheliomatous hyperplasia and/or papillomatosis of a varying degree.^1,2,5 Of note, suprabasal acantholysis is usually overshadowed by the changes in PV and presents only focally, as in our patient. The most common autoantibody profile is IgG targeting Dsg3; however, a spectrum of other autoantibodies has been identified, such as IgG antidesmocollin 3, IgA anti-Dsg3, and IgG anti-Dsg1.^8,9

The most important differential diagnosis of PV is pyodermatitis-pyostomatitis vegetans. These 2 entities share many clinical and histopathological features; however, direct immunofluorescence is helpfulfor differentiation because it generally is negative in pyodermatitis-pyostomatitis vegetans.^2,10 Furthermore, there is a well-established association between pyodermatitis-pyostomatitis vegetans and inflammatory bowel disorders, whereas PV has anecdotally been linked to malignancy, human immunodeficiency virus infection, and heroin abuse.^1,2,10 Our patient was seronegative for human immunodeficiency virus and denied weight loss or loss of appetite. For those cases of PV involving a single anatomic site, the differential diagnosis is broader and encompasses dermatoses such as verrucae, syphilitic chancre, condylomata lata, granuloma inguinale, herpes simplex virus infection, and Kaposi sarcoma.

Treatment of PV is similar to pemphigus vulgaris and consists of a combination of systemic corticosteroids and steroid-sparing agents.^1,5 On the other hand, more limited presentations of PV may be suitable for intralesional treatment with triamcinolone acetonide, thus avoiding potential adverse effects of systemic therapy.^1,2 In our case with localized involvement, a favorable response was obtained with intralesional triamcinolone acetonide, and we plan to utilize systemic corticosteroids if the disease becomes generalized during follow-up.

To improve patient care and outcomes, leading dermatologists from the Cutis Editorial Board answered 5 questions on pediatric skin care. Here’s what we found.

Do you recommend sunscreen in babies younger than 6 months?

More than half (64%) of dermatologists we surveyed do not recommend using sunscreens in babies younger than 6 months; they should stay out of the sun. They recommended sun-protective clothing, hats, and sunglasses in this age group.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

Babies younger than 6 months are still developing barrier functionality and have a higher surface area to body weight ratio compared to older children and adults. There is decreased UV light barrier protection and increased risk for systemic drug absorption. Therefore, it is best to avoid sunscreen in babies younger than 6 months. Instead, I recommend avoiding sunlight during peak hours, keeping babies in the shade, and dressing them in sun-protective clothing and hats.

Next page: Bathing and eczema

What advice do you give parents/guardians on bathing for babies with eczema?

Two-thirds of dermatologists (68%) indicated that moisturizers should be applied after bathing babies with eczema. More than half (64%) suggested using fragrance-free cleansers. Results varied on the frequency of bathing; 32% said bathe once daily for short periods with warm water, and 41% suggested to reduce bathing to a few nights a week.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

Dry skin is a characteristic feature of atopic dermatitis. We now know that skin barrier dysfunction, such as filaggrin deficiency, contributes to the pathophysiology in some patients. In addition, a paucity of stratum corneum and intercellular lipids increases transepidermal water loss. Therefore, emollients containing humectants to augment stratum corneum hydration and occludents to reduce evaporation are extremely helpful in maintenance treatment of atopic dermatitis.

Next page: Nonsteroidal agents

Do you prescribe nonsteroidal agents for children younger than 2 years?

Almost two-thirds (64%) of dermatologists do prescribe nonsteroidal agents for children younger than 2 years.

If yes, which nonsteroidal agents do you prescribe for children?

Of those dermatologists who indicated that they do prescribe nonsteroidal agents for children younger than 2 years, almost half (45%) prescribe pimecrolimus, while 36% prescribe crisaborole or tacrolimus.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

We have limited options for US Food and Drug Administration (FDA)–approved therapies for atopic dermatitis in children younger than 2 years. The risks of adverse effects also are higher in younger children compared to older children and adults, particularly hypothalamic-pituitary-adrenal suppression with corticosteroids. Pimecrolimus was the most common nonsteroidal prescribed in this group. It should be noted that pimecrolimus is not FDA approved for use in children younger than 2 years; however, 2 phase 3 studies were conducted with 436 infants aged 3 months to 23 months and they demonstrated safety and efficacy.

Next page: Procedures in adolescents

Which procedures do you perform on adolescents?
Forty-one percent of dermatologists surveyed indicated that they do not perform procedures on adolescents. Of those that do, 32% use laser hair removal or chemical peels in adolescents, while only 23% each use light therapy for acne or onabotulinumtoxinA for hyperhidrosis. Pulsed dye laser use was reported in only 18% of dermatologists.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

The results of this survey are a reflection of the relatively recent trends in dermatology training. Now that there is board certification in pediatric dermatology, many dermatologists now refer to pediatric dermatologists for children who need or want procedures.

Next page: More tips from derms

More Tips From Dermatologists

The dermatologists we polled had the following advice for their peers:

Keep the regimen as simple as possible and make sure your skin care advice is culturally relevant.—Craig Burkhart, MD (Chapel Hill, North Carolina)

Please, avoid direct sun exposure as much as possible by wearing protective garments and finding shades in the outside.—Jisun Cha, MD (New Brunswick, New Jersey)

Good habits start early. Teach children how to care for their skin and they will carry that practice with them over the course of their  lifetime, and hopefully pass it on.—James Q. Del Rosso, DO (Las Vegas, Nevada)

About This Survey
The survey was fielded electronically to Cutis Editorial Board Members within the United States from September 13, 2018, to October 4, 2018. A total of 22 usable responses were received.

To improve patient care and outcomes, leading dermatologists from the Cutis Editorial Board answered 5 questions on pediatric skin care. Here’s what we found.

Do you recommend sunscreen in babies younger than 6 months?

More than half (64%) of dermatologists we surveyed do not recommend using sunscreens in babies younger than 6 months; they should stay out of the sun. They recommended sun-protective clothing, hats, and sunglasses in this age group.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

Babies younger than 6 months are still developing barrier functionality and have a higher surface area to body weight ratio compared to older children and adults. There is decreased UV light barrier protection and increased risk for systemic drug absorption. Therefore, it is best to avoid sunscreen in babies younger than 6 months. Instead, I recommend avoiding sunlight during peak hours, keeping babies in the shade, and dressing them in sun-protective clothing and hats.

Next page: Bathing and eczema

What advice do you give parents/guardians on bathing for babies with eczema?

Two-thirds of dermatologists (68%) indicated that moisturizers should be applied after bathing babies with eczema. More than half (64%) suggested using fragrance-free cleansers. Results varied on the frequency of bathing; 32% said bathe once daily for short periods with warm water, and 41% suggested to reduce bathing to a few nights a week.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

Dry skin is a characteristic feature of atopic dermatitis. We now know that skin barrier dysfunction, such as filaggrin deficiency, contributes to the pathophysiology in some patients. In addition, a paucity of stratum corneum and intercellular lipids increases transepidermal water loss. Therefore, emollients containing humectants to augment stratum corneum hydration and occludents to reduce evaporation are extremely helpful in maintenance treatment of atopic dermatitis.

Next page: Nonsteroidal agents

Do you prescribe nonsteroidal agents for children younger than 2 years?

Almost two-thirds (64%) of dermatologists do prescribe nonsteroidal agents for children younger than 2 years.

If yes, which nonsteroidal agents do you prescribe for children?

Of those dermatologists who indicated that they do prescribe nonsteroidal agents for children younger than 2 years, almost half (45%) prescribe pimecrolimus, while 36% prescribe crisaborole or tacrolimus.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

We have limited options for US Food and Drug Administration (FDA)–approved therapies for atopic dermatitis in children younger than 2 years. The risks of adverse effects also are higher in younger children compared to older children and adults, particularly hypothalamic-pituitary-adrenal suppression with corticosteroids. Pimecrolimus was the most common nonsteroidal prescribed in this group. It should be noted that pimecrolimus is not FDA approved for use in children younger than 2 years; however, 2 phase 3 studies were conducted with 436 infants aged 3 months to 23 months and they demonstrated safety and efficacy.

Next page: Procedures in adolescents

Which procedures do you perform on adolescents?
Forty-one percent of dermatologists surveyed indicated that they do not perform procedures on adolescents. Of those that do, 32% use laser hair removal or chemical peels in adolescents, while only 23% each use light therapy for acne or onabotulinumtoxinA for hyperhidrosis. Pulsed dye laser use was reported in only 18% of dermatologists.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

The results of this survey are a reflection of the relatively recent trends in dermatology training. Now that there is board certification in pediatric dermatology, many dermatologists now refer to pediatric dermatologists for children who need or want procedures.

Next page: More tips from derms

More Tips From Dermatologists

The dermatologists we polled had the following advice for their peers:

Keep the regimen as simple as possible and make sure your skin care advice is culturally relevant.—Craig Burkhart, MD (Chapel Hill, North Carolina)

Please, avoid direct sun exposure as much as possible by wearing protective garments and finding shades in the outside.—Jisun Cha, MD (New Brunswick, New Jersey)

Good habits start early. Teach children how to care for their skin and they will carry that practice with them over the course of their  lifetime, and hopefully pass it on.—James Q. Del Rosso, DO (Las Vegas, Nevada)

About This Survey
The survey was fielded electronically to Cutis Editorial Board Members within the United States from September 13, 2018, to October 4, 2018. A total of 22 usable responses were received.

To improve patient care and outcomes, leading dermatologists from the Cutis Editorial Board answered 5 questions on pediatric skin care. Here’s what we found.

Do you recommend sunscreen in babies younger than 6 months?

More than half (64%) of dermatologists we surveyed do not recommend using sunscreens in babies younger than 6 months; they should stay out of the sun. They recommended sun-protective clothing, hats, and sunglasses in this age group.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

Babies younger than 6 months are still developing barrier functionality and have a higher surface area to body weight ratio compared to older children and adults. There is decreased UV light barrier protection and increased risk for systemic drug absorption. Therefore, it is best to avoid sunscreen in babies younger than 6 months. Instead, I recommend avoiding sunlight during peak hours, keeping babies in the shade, and dressing them in sun-protective clothing and hats.

Next page: Bathing and eczema

What advice do you give parents/guardians on bathing for babies with eczema?

Two-thirds of dermatologists (68%) indicated that moisturizers should be applied after bathing babies with eczema. More than half (64%) suggested using fragrance-free cleansers. Results varied on the frequency of bathing; 32% said bathe once daily for short periods with warm water, and 41% suggested to reduce bathing to a few nights a week.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

Dry skin is a characteristic feature of atopic dermatitis. We now know that skin barrier dysfunction, such as filaggrin deficiency, contributes to the pathophysiology in some patients. In addition, a paucity of stratum corneum and intercellular lipids increases transepidermal water loss. Therefore, emollients containing humectants to augment stratum corneum hydration and occludents to reduce evaporation are extremely helpful in maintenance treatment of atopic dermatitis.

Next page: Nonsteroidal agents

Do you prescribe nonsteroidal agents for children younger than 2 years?

Almost two-thirds (64%) of dermatologists do prescribe nonsteroidal agents for children younger than 2 years.

If yes, which nonsteroidal agents do you prescribe for children?

Of those dermatologists who indicated that they do prescribe nonsteroidal agents for children younger than 2 years, almost half (45%) prescribe pimecrolimus, while 36% prescribe crisaborole or tacrolimus.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

We have limited options for US Food and Drug Administration (FDA)–approved therapies for atopic dermatitis in children younger than 2 years. The risks of adverse effects also are higher in younger children compared to older children and adults, particularly hypothalamic-pituitary-adrenal suppression with corticosteroids. Pimecrolimus was the most common nonsteroidal prescribed in this group. It should be noted that pimecrolimus is not FDA approved for use in children younger than 2 years; however, 2 phase 3 studies were conducted with 436 infants aged 3 months to 23 months and they demonstrated safety and efficacy.

Next page: Procedures in adolescents

Which procedures do you perform on adolescents?
Forty-one percent of dermatologists surveyed indicated that they do not perform procedures on adolescents. Of those that do, 32% use laser hair removal or chemical peels in adolescents, while only 23% each use light therapy for acne or onabotulinumtoxinA for hyperhidrosis. Pulsed dye laser use was reported in only 18% of dermatologists.

Expert Commentary
Provided by Shari R. Lipner, MD, PhD (New York, New York)

The results of this survey are a reflection of the relatively recent trends in dermatology training. Now that there is board certification in pediatric dermatology, many dermatologists now refer to pediatric dermatologists for children who need or want procedures.

Next page: More tips from derms

More Tips From Dermatologists

The dermatologists we polled had the following advice for their peers:

Keep the regimen as simple as possible and make sure your skin care advice is culturally relevant.—Craig Burkhart, MD (Chapel Hill, North Carolina)

Please, avoid direct sun exposure as much as possible by wearing protective garments and finding shades in the outside.—Jisun Cha, MD (New Brunswick, New Jersey)

Good habits start early. Teach children how to care for their skin and they will carry that practice with them over the course of their  lifetime, and hopefully pass it on.—James Q. Del Rosso, DO (Las Vegas, Nevada)

About This Survey
The survey was fielded electronically to Cutis Editorial Board Members within the United States from September 13, 2018, to October 4, 2018. A total of 22 usable responses were received.

Angiosarcoma is a rare and aggressive vascular malignant neoplasm derived from endothelial cells. In general, sarcomas account for approximately 1% of all malignancies, with approximately 2% being angiosarcomas.¹ The risk of recurrence at 5 years is estimated to be 84%, and 5-year survival is estimated at 15% to 30%. Poor prognostic factors for angiosarcoma include large tumor size, depth of invasion greater than 3 mm, high mitotic rate, positive surgical margins, and metastasis.² Approximately 20% to 40% of patients who are diagnosed with angiosarcoma already have distant metastasis, contributing to the aggressive nature of this neoplasm.³

Angiosarcoma can affect various anatomic locations, including the skin, soft tissue, breasts, and liver. Cutaneous angiosarcoma is the most common clinical manifestation, accounting for approximately 50% to 60% of all cases, and typically is known to occur in 3 distinct settings.² Primary or idiopathic cutaneous angiosarcoma is most commonly seen in elderly individuals, with a peak incidence in the seventh to eighth decades of life, and presents as a bruiselike lesion predominantly on the head and neck. Angiosarcoma also is seen clinically in patients exposed to radiation treatment, with a median onset of symptoms occurring 5 to 10 years posttreatment, and in patients with chronic lymphedema, usually on the arm following radical mastectomy, which also is known as Stewart-Treves syndrome.²

With any sarcoma, treatment typically first involves surgical excision; however, there is no direct approach for treatment of cutaneous angiosarcoma, as an individual plan typically is needed for each patient. Treatment options include surgical excision, radiation, chemotherapy, or a combination of these therapies.^2,4

We present a rare case of cutaneous angiosarcoma of the left leg in the setting of chronic venous insufficiency with some degree of lymphedema and a nonhealing ulcer. This case is unique in that it does not fit the classic presentation of cutaneous angiosarcoma previously described.

Case Report

An 83-year-old woman with a medical history of advanced dementia, congestive heart failure, chronic obstructive pulmonary disease, chronic kidney disease, type 2 diabetes mellitus, hypertension, and chronic venous insufficiency with stasis dermatitis presented to the emergency department following a mechanical fall. Most of her medical history was obtained from the patient’s family. She had a history of multiple falls originally thought to be related to a chronic leg ulcer that had been managed with wound care. Recently, however, the lesion was noted to have increasing erythema surrounding the wound margins. An 8×8-cm erythematous plaque on the anterior lateral left leg with a firm central nodule with hemorrhagic crust that measured approximately 4 cm in diameter was noted by the emergency department physicians (Figure 1). In the emergency department, vitals and other laboratory values were within reference range, and a radiograph of the left tibia/fibula was unremarkable. Cellulitis initially was considered in the emergency department and cephalexin was started; however, since the patient was afebrile and had no leukocytosis, plastic surgery also was consulted. Biopsies were obtained from the superior and inferior parts of the lesion. Histologic analysis revealed a poorly differentiated vascular neoplasm of epithelioid endothelial cells with considerable cell atypia that extended through the entirety of the dermis (Figure 2). The tumor cells stained positive with vimentin and CD34. Pathology noted no immunohistochemistry stains to synaptophysin, S-100, human melanoma black 45, MART-1, CK20, CK7, CK8/18, CK5/6, and p63. The pathologic diagnosis was consistent with cutaneous angiosarcoma. Computed tomography of the chest, abdomen, and pelvis revealed no local or distant metastases.

A wide excision of the cutaneous angiosarcoma was performed. The initial frozen section analysis revealed positive margins. Three additional excisions still showed positive margins, and further excision was held after obtaining family consent due to the extensive nature of the neoplasm and lengthy operating room time. The final defect after excision measured 15×10×2.5 cm (Figure 3A), and subsequent application of a split-thickness graft was performed. Additional treatment options were discussed with the family, including radiation therapy, amputation of the left lower leg, or no treatment. The family opted not to proceed with further treatment. The graft healed without signs of reoccurrence approximately 3 months later (Figure 3B), and the patient received physical therapy, which allowed her to gain strength and some independence.

Comment

Clinical Manifestation
Cutaneous angiosarcoma is a rare malignant vascular neoplasm that when clinically diagnosed is typically seen in 3 settings: (1) idiopathic (commonly on the face and neck), (2) following radiation treatment, and (3) classically following mastectomy with subsequent chronic lymphedema. Our patient did not classically fit these settings of cutaneous angiosarcoma due to the location of the lesion on the lower leg as well as its occurrence in the setting of a chronic nonhealing ulcer and lymphedema.

Chronic lymphedema is a common clinical manifestation that is likely secondary to other medical conditions, such as in our patient. As a result, these patients are at increased risk for developing chronic ulcers due to poor wound healing; however, as seen in our patient, chronic nonhealing ulcers require a broad differential because they may clinically mimic many processes. Patient history and visual presentation were crucial in this case because a biopsy was obtained that ultimately led to the patient’s diagnosis.

Differential Diagnosis
Initially, a venous ulcer secondary to chronic venous insufficiency was considered in the differential for our patient. She had a history of congestive heart failure, kidney disease, and type 2 diabetes mellitus, all of which contribute to lymphedema and/or poor wound healing. However, venous ulcers usually are located on the medial ankles and are irregularly shaped with an erythematous border and fibrinous exudate with central depression, making it a less likely diagnosis in our patient. Additionally, an infectious process was considered, but the patient was afebrile and laboratory values demonstrated no leukocytosis.

Marjolin ulcer was highly suspected because the clinical presentation revealed a nodule with hemorrhagic crust and induration in the setting of a chronic nonhealing ulcer. The pathogenesis of malignancy in chronic ulcers is thought to be due to continuous mitotic activity from regeneration and repair of the wound, especially in the setting of repeated trauma to the area.⁵ In our patient, the history of multiple falls with possible multitrauma injury to the chronic ulcer further increased suspicion of malignancy. The most common and frequently seen malignancy that develops in chronic ulcers is squamous cell carcinoma (SCC) followed by basal cell carcinoma. Plastic surgery suspected an SCC for the working diagnosis, which prompted a punch biopsy; however, the histologic analysis was not consistent with SCC or basal cell carcinoma. Marjolin ulcer also may demonstrate a periosteal reaction,⁵ which was not the case with our patient after a radiograph of the left tibia/fibula was unremarkable.

Another potential malignancy to consider is melanoma. There are few case reports of biopsy-proven melanoma from an enlarging chronic ulcer.^6,7 Additionally, poorly differentiated angiosarcoma can mimic melanoma²; however, immunohistochemistry stain was negative for S-100, human melanoma black 45, and MART-1, making melanoma unlikely.

Kaposi sarcoma (KS) and angiosarcoma are both malignant vascular tumors that similarly present with red to purple patches, plaques, or nodules, making it difficult to distinguish between the two conditions. It is important to note that KS usually is lower grade, and the pathogenesis is linked to human herpesvirus 8, which can be identified on immunohistochemistry staining. There have been cases of KS reported in patients who have no history of human immunodeficiency virus/AIDS, thus the classic subtype of KS may have been considered in this patient.⁸ The histologic appearance of KS may vary from dilated irregular endothelial cells lining the vascular space to mild endothelial cell atypia. Histology also shows hemosiderin-laden macrophages, extravasated red blood cells, and an inflammatory infiltrate. An additional malignant vascular neoplasm that needs to be differentiated is epithelioid hemangioendothelioma. Cutaneous presentation of an epithelioid hemangioendothelioma may be similar to what was seen in our patient but histologically will usually show neoplastic cells with pale eosinophilic cytoplasm and vesicular nuclei of plump, oval, polygonal cells in cords or aggregates surrounding vascular channels. These neoplasms also tend to occur around medium- to large-sized veins.^1,9 With our patient, even though human herpesvirus 8 was not tested with immunohistochemistry, gold standard immunohistochemistry confirmation with CD34 and vimentin staining combined with poorly differentiated endothelial atypia with mitotic figures on histologic analysis favored angiosarcoma versus KS or epithelioid hemangioendothelioma.^10,11

Management
Cutaneous angiosarcoma is a rare and aggressive vascular neoplasm accounting for approximately 2% of all combined sarcomas, with an estimated 20% to 40% having distant metastasis at diagnosis.^1,3 For this reason, computed tomography was performed in our patient and revealed no local or distant metastasis. Therefore, chemotherapy was not an appropriate adjuvant treatment option.¹² With no evidence of metastasis, initial treatment began with surgical removal but proved to be difficult in our patient. Although the implications of positive surgical margins remain unclear with regard to overall patient survival, surgical resection followed by radiation therapy has been shown to be optimal, as it reduces the risk of local reoccurrence.³ There have been reported cases of cutaneous angiosarcoma of the leg that were treated with amputation without signs of reoccurrence or metastasis.^10,13,14 Given the results from these cases and considering that our patient had no metastasis, amputation seemed to be a good prognostic option; however, considering other factors regarding the patient’s comorbidities and quality of life, her family decided not to pursue any further treatment with amputation or radiation therapy.

Conclusion

There should be low threshold for biopsy in patients who present with nonhealing wounds that do not progress in the normal phase of wound healing with suspicion for malignancy. As seen with our patient, cutaneous angiosarcoma can clinically mimic many disease processes, and although rare in nature, it should always be considered when a patient presents with a rapidly growing lesion in the setting of chronic lymphedema or venous ulcer.

Angiosarcoma is a rare and aggressive vascular malignant neoplasm derived from endothelial cells. In general, sarcomas account for approximately 1% of all malignancies, with approximately 2% being angiosarcomas.¹ The risk of recurrence at 5 years is estimated to be 84%, and 5-year survival is estimated at 15% to 30%. Poor prognostic factors for angiosarcoma include large tumor size, depth of invasion greater than 3 mm, high mitotic rate, positive surgical margins, and metastasis.² Approximately 20% to 40% of patients who are diagnosed with angiosarcoma already have distant metastasis, contributing to the aggressive nature of this neoplasm.³

Angiosarcoma can affect various anatomic locations, including the skin, soft tissue, breasts, and liver. Cutaneous angiosarcoma is the most common clinical manifestation, accounting for approximately 50% to 60% of all cases, and typically is known to occur in 3 distinct settings.² Primary or idiopathic cutaneous angiosarcoma is most commonly seen in elderly individuals, with a peak incidence in the seventh to eighth decades of life, and presents as a bruiselike lesion predominantly on the head and neck. Angiosarcoma also is seen clinically in patients exposed to radiation treatment, with a median onset of symptoms occurring 5 to 10 years posttreatment, and in patients with chronic lymphedema, usually on the arm following radical mastectomy, which also is known as Stewart-Treves syndrome.²

With any sarcoma, treatment typically first involves surgical excision; however, there is no direct approach for treatment of cutaneous angiosarcoma, as an individual plan typically is needed for each patient. Treatment options include surgical excision, radiation, chemotherapy, or a combination of these therapies.^2,4

We present a rare case of cutaneous angiosarcoma of the left leg in the setting of chronic venous insufficiency with some degree of lymphedema and a nonhealing ulcer. This case is unique in that it does not fit the classic presentation of cutaneous angiosarcoma previously described.

Case Report

An 83-year-old woman with a medical history of advanced dementia, congestive heart failure, chronic obstructive pulmonary disease, chronic kidney disease, type 2 diabetes mellitus, hypertension, and chronic venous insufficiency with stasis dermatitis presented to the emergency department following a mechanical fall. Most of her medical history was obtained from the patient’s family. She had a history of multiple falls originally thought to be related to a chronic leg ulcer that had been managed with wound care. Recently, however, the lesion was noted to have increasing erythema surrounding the wound margins. An 8×8-cm erythematous plaque on the anterior lateral left leg with a firm central nodule with hemorrhagic crust that measured approximately 4 cm in diameter was noted by the emergency department physicians (Figure 1). In the emergency department, vitals and other laboratory values were within reference range, and a radiograph of the left tibia/fibula was unremarkable. Cellulitis initially was considered in the emergency department and cephalexin was started; however, since the patient was afebrile and had no leukocytosis, plastic surgery also was consulted. Biopsies were obtained from the superior and inferior parts of the lesion. Histologic analysis revealed a poorly differentiated vascular neoplasm of epithelioid endothelial cells with considerable cell atypia that extended through the entirety of the dermis (Figure 2). The tumor cells stained positive with vimentin and CD34. Pathology noted no immunohistochemistry stains to synaptophysin, S-100, human melanoma black 45, MART-1, CK20, CK7, CK8/18, CK5/6, and p63. The pathologic diagnosis was consistent with cutaneous angiosarcoma. Computed tomography of the chest, abdomen, and pelvis revealed no local or distant metastases.

A wide excision of the cutaneous angiosarcoma was performed. The initial frozen section analysis revealed positive margins. Three additional excisions still showed positive margins, and further excision was held after obtaining family consent due to the extensive nature of the neoplasm and lengthy operating room time. The final defect after excision measured 15×10×2.5 cm (Figure 3A), and subsequent application of a split-thickness graft was performed. Additional treatment options were discussed with the family, including radiation therapy, amputation of the left lower leg, or no treatment. The family opted not to proceed with further treatment. The graft healed without signs of reoccurrence approximately 3 months later (Figure 3B), and the patient received physical therapy, which allowed her to gain strength and some independence.

Comment

Clinical Manifestation
Cutaneous angiosarcoma is a rare malignant vascular neoplasm that when clinically diagnosed is typically seen in 3 settings: (1) idiopathic (commonly on the face and neck), (2) following radiation treatment, and (3) classically following mastectomy with subsequent chronic lymphedema. Our patient did not classically fit these settings of cutaneous angiosarcoma due to the location of the lesion on the lower leg as well as its occurrence in the setting of a chronic nonhealing ulcer and lymphedema.

Chronic lymphedema is a common clinical manifestation that is likely secondary to other medical conditions, such as in our patient. As a result, these patients are at increased risk for developing chronic ulcers due to poor wound healing; however, as seen in our patient, chronic nonhealing ulcers require a broad differential because they may clinically mimic many processes. Patient history and visual presentation were crucial in this case because a biopsy was obtained that ultimately led to the patient’s diagnosis.

Differential Diagnosis
Initially, a venous ulcer secondary to chronic venous insufficiency was considered in the differential for our patient. She had a history of congestive heart failure, kidney disease, and type 2 diabetes mellitus, all of which contribute to lymphedema and/or poor wound healing. However, venous ulcers usually are located on the medial ankles and are irregularly shaped with an erythematous border and fibrinous exudate with central depression, making it a less likely diagnosis in our patient. Additionally, an infectious process was considered, but the patient was afebrile and laboratory values demonstrated no leukocytosis.

Marjolin ulcer was highly suspected because the clinical presentation revealed a nodule with hemorrhagic crust and induration in the setting of a chronic nonhealing ulcer. The pathogenesis of malignancy in chronic ulcers is thought to be due to continuous mitotic activity from regeneration and repair of the wound, especially in the setting of repeated trauma to the area.⁵ In our patient, the history of multiple falls with possible multitrauma injury to the chronic ulcer further increased suspicion of malignancy. The most common and frequently seen malignancy that develops in chronic ulcers is squamous cell carcinoma (SCC) followed by basal cell carcinoma. Plastic surgery suspected an SCC for the working diagnosis, which prompted a punch biopsy; however, the histologic analysis was not consistent with SCC or basal cell carcinoma. Marjolin ulcer also may demonstrate a periosteal reaction,⁵ which was not the case with our patient after a radiograph of the left tibia/fibula was unremarkable.

Another potential malignancy to consider is melanoma. There are few case reports of biopsy-proven melanoma from an enlarging chronic ulcer.^6,7 Additionally, poorly differentiated angiosarcoma can mimic melanoma²; however, immunohistochemistry stain was negative for S-100, human melanoma black 45, and MART-1, making melanoma unlikely.

Kaposi sarcoma (KS) and angiosarcoma are both malignant vascular tumors that similarly present with red to purple patches, plaques, or nodules, making it difficult to distinguish between the two conditions. It is important to note that KS usually is lower grade, and the pathogenesis is linked to human herpesvirus 8, which can be identified on immunohistochemistry staining. There have been cases of KS reported in patients who have no history of human immunodeficiency virus/AIDS, thus the classic subtype of KS may have been considered in this patient.⁸ The histologic appearance of KS may vary from dilated irregular endothelial cells lining the vascular space to mild endothelial cell atypia. Histology also shows hemosiderin-laden macrophages, extravasated red blood cells, and an inflammatory infiltrate. An additional malignant vascular neoplasm that needs to be differentiated is epithelioid hemangioendothelioma. Cutaneous presentation of an epithelioid hemangioendothelioma may be similar to what was seen in our patient but histologically will usually show neoplastic cells with pale eosinophilic cytoplasm and vesicular nuclei of plump, oval, polygonal cells in cords or aggregates surrounding vascular channels. These neoplasms also tend to occur around medium- to large-sized veins.^1,9 With our patient, even though human herpesvirus 8 was not tested with immunohistochemistry, gold standard immunohistochemistry confirmation with CD34 and vimentin staining combined with poorly differentiated endothelial atypia with mitotic figures on histologic analysis favored angiosarcoma versus KS or epithelioid hemangioendothelioma.^10,11

Management
Cutaneous angiosarcoma is a rare and aggressive vascular neoplasm accounting for approximately 2% of all combined sarcomas, with an estimated 20% to 40% having distant metastasis at diagnosis.^1,3 For this reason, computed tomography was performed in our patient and revealed no local or distant metastasis. Therefore, chemotherapy was not an appropriate adjuvant treatment option.¹² With no evidence of metastasis, initial treatment began with surgical removal but proved to be difficult in our patient. Although the implications of positive surgical margins remain unclear with regard to overall patient survival, surgical resection followed by radiation therapy has been shown to be optimal, as it reduces the risk of local reoccurrence.³ There have been reported cases of cutaneous angiosarcoma of the leg that were treated with amputation without signs of reoccurrence or metastasis.^10,13,14 Given the results from these cases and considering that our patient had no metastasis, amputation seemed to be a good prognostic option; however, considering other factors regarding the patient’s comorbidities and quality of life, her family decided not to pursue any further treatment with amputation or radiation therapy.

Conclusion

There should be low threshold for biopsy in patients who present with nonhealing wounds that do not progress in the normal phase of wound healing with suspicion for malignancy. As seen with our patient, cutaneous angiosarcoma can clinically mimic many disease processes, and although rare in nature, it should always be considered when a patient presents with a rapidly growing lesion in the setting of chronic lymphedema or venous ulcer.

Angiosarcoma is a rare and aggressive vascular malignant neoplasm derived from endothelial cells. In general, sarcomas account for approximately 1% of all malignancies, with approximately 2% being angiosarcomas.¹ The risk of recurrence at 5 years is estimated to be 84%, and 5-year survival is estimated at 15% to 30%. Poor prognostic factors for angiosarcoma include large tumor size, depth of invasion greater than 3 mm, high mitotic rate, positive surgical margins, and metastasis.² Approximately 20% to 40% of patients who are diagnosed with angiosarcoma already have distant metastasis, contributing to the aggressive nature of this neoplasm.³

Angiosarcoma can affect various anatomic locations, including the skin, soft tissue, breasts, and liver. Cutaneous angiosarcoma is the most common clinical manifestation, accounting for approximately 50% to 60% of all cases, and typically is known to occur in 3 distinct settings.² Primary or idiopathic cutaneous angiosarcoma is most commonly seen in elderly individuals, with a peak incidence in the seventh to eighth decades of life, and presents as a bruiselike lesion predominantly on the head and neck. Angiosarcoma also is seen clinically in patients exposed to radiation treatment, with a median onset of symptoms occurring 5 to 10 years posttreatment, and in patients with chronic lymphedema, usually on the arm following radical mastectomy, which also is known as Stewart-Treves syndrome.²

With any sarcoma, treatment typically first involves surgical excision; however, there is no direct approach for treatment of cutaneous angiosarcoma, as an individual plan typically is needed for each patient. Treatment options include surgical excision, radiation, chemotherapy, or a combination of these therapies.^2,4

We present a rare case of cutaneous angiosarcoma of the left leg in the setting of chronic venous insufficiency with some degree of lymphedema and a nonhealing ulcer. This case is unique in that it does not fit the classic presentation of cutaneous angiosarcoma previously described.

Case Report

An 83-year-old woman with a medical history of advanced dementia, congestive heart failure, chronic obstructive pulmonary disease, chronic kidney disease, type 2 diabetes mellitus, hypertension, and chronic venous insufficiency with stasis dermatitis presented to the emergency department following a mechanical fall. Most of her medical history was obtained from the patient’s family. She had a history of multiple falls originally thought to be related to a chronic leg ulcer that had been managed with wound care. Recently, however, the lesion was noted to have increasing erythema surrounding the wound margins. An 8×8-cm erythematous plaque on the anterior lateral left leg with a firm central nodule with hemorrhagic crust that measured approximately 4 cm in diameter was noted by the emergency department physicians (Figure 1). In the emergency department, vitals and other laboratory values were within reference range, and a radiograph of the left tibia/fibula was unremarkable. Cellulitis initially was considered in the emergency department and cephalexin was started; however, since the patient was afebrile and had no leukocytosis, plastic surgery also was consulted. Biopsies were obtained from the superior and inferior parts of the lesion. Histologic analysis revealed a poorly differentiated vascular neoplasm of epithelioid endothelial cells with considerable cell atypia that extended through the entirety of the dermis (Figure 2). The tumor cells stained positive with vimentin and CD34. Pathology noted no immunohistochemistry stains to synaptophysin, S-100, human melanoma black 45, MART-1, CK20, CK7, CK8/18, CK5/6, and p63. The pathologic diagnosis was consistent with cutaneous angiosarcoma. Computed tomography of the chest, abdomen, and pelvis revealed no local or distant metastases.

A wide excision of the cutaneous angiosarcoma was performed. The initial frozen section analysis revealed positive margins. Three additional excisions still showed positive margins, and further excision was held after obtaining family consent due to the extensive nature of the neoplasm and lengthy operating room time. The final defect after excision measured 15×10×2.5 cm (Figure 3A), and subsequent application of a split-thickness graft was performed. Additional treatment options were discussed with the family, including radiation therapy, amputation of the left lower leg, or no treatment. The family opted not to proceed with further treatment. The graft healed without signs of reoccurrence approximately 3 months later (Figure 3B), and the patient received physical therapy, which allowed her to gain strength and some independence.

Comment

Clinical Manifestation
Cutaneous angiosarcoma is a rare malignant vascular neoplasm that when clinically diagnosed is typically seen in 3 settings: (1) idiopathic (commonly on the face and neck), (2) following radiation treatment, and (3) classically following mastectomy with subsequent chronic lymphedema. Our patient did not classically fit these settings of cutaneous angiosarcoma due to the location of the lesion on the lower leg as well as its occurrence in the setting of a chronic nonhealing ulcer and lymphedema.

Chronic lymphedema is a common clinical manifestation that is likely secondary to other medical conditions, such as in our patient. As a result, these patients are at increased risk for developing chronic ulcers due to poor wound healing; however, as seen in our patient, chronic nonhealing ulcers require a broad differential because they may clinically mimic many processes. Patient history and visual presentation were crucial in this case because a biopsy was obtained that ultimately led to the patient’s diagnosis.

Differential Diagnosis
Initially, a venous ulcer secondary to chronic venous insufficiency was considered in the differential for our patient. She had a history of congestive heart failure, kidney disease, and type 2 diabetes mellitus, all of which contribute to lymphedema and/or poor wound healing. However, venous ulcers usually are located on the medial ankles and are irregularly shaped with an erythematous border and fibrinous exudate with central depression, making it a less likely diagnosis in our patient. Additionally, an infectious process was considered, but the patient was afebrile and laboratory values demonstrated no leukocytosis.

Marjolin ulcer was highly suspected because the clinical presentation revealed a nodule with hemorrhagic crust and induration in the setting of a chronic nonhealing ulcer. The pathogenesis of malignancy in chronic ulcers is thought to be due to continuous mitotic activity from regeneration and repair of the wound, especially in the setting of repeated trauma to the area.⁵ In our patient, the history of multiple falls with possible multitrauma injury to the chronic ulcer further increased suspicion of malignancy. The most common and frequently seen malignancy that develops in chronic ulcers is squamous cell carcinoma (SCC) followed by basal cell carcinoma. Plastic surgery suspected an SCC for the working diagnosis, which prompted a punch biopsy; however, the histologic analysis was not consistent with SCC or basal cell carcinoma. Marjolin ulcer also may demonstrate a periosteal reaction,⁵ which was not the case with our patient after a radiograph of the left tibia/fibula was unremarkable.

Another potential malignancy to consider is melanoma. There are few case reports of biopsy-proven melanoma from an enlarging chronic ulcer.^6,7 Additionally, poorly differentiated angiosarcoma can mimic melanoma²; however, immunohistochemistry stain was negative for S-100, human melanoma black 45, and MART-1, making melanoma unlikely.

Kaposi sarcoma (KS) and angiosarcoma are both malignant vascular tumors that similarly present with red to purple patches, plaques, or nodules, making it difficult to distinguish between the two conditions. It is important to note that KS usually is lower grade, and the pathogenesis is linked to human herpesvirus 8, which can be identified on immunohistochemistry staining. There have been cases of KS reported in patients who have no history of human immunodeficiency virus/AIDS, thus the classic subtype of KS may have been considered in this patient.⁸ The histologic appearance of KS may vary from dilated irregular endothelial cells lining the vascular space to mild endothelial cell atypia. Histology also shows hemosiderin-laden macrophages, extravasated red blood cells, and an inflammatory infiltrate. An additional malignant vascular neoplasm that needs to be differentiated is epithelioid hemangioendothelioma. Cutaneous presentation of an epithelioid hemangioendothelioma may be similar to what was seen in our patient but histologically will usually show neoplastic cells with pale eosinophilic cytoplasm and vesicular nuclei of plump, oval, polygonal cells in cords or aggregates surrounding vascular channels. These neoplasms also tend to occur around medium- to large-sized veins.^1,9 With our patient, even though human herpesvirus 8 was not tested with immunohistochemistry, gold standard immunohistochemistry confirmation with CD34 and vimentin staining combined with poorly differentiated endothelial atypia with mitotic figures on histologic analysis favored angiosarcoma versus KS or epithelioid hemangioendothelioma.^10,11

Management
Cutaneous angiosarcoma is a rare and aggressive vascular neoplasm accounting for approximately 2% of all combined sarcomas, with an estimated 20% to 40% having distant metastasis at diagnosis.^1,3 For this reason, computed tomography was performed in our patient and revealed no local or distant metastasis. Therefore, chemotherapy was not an appropriate adjuvant treatment option.¹² With no evidence of metastasis, initial treatment began with surgical removal but proved to be difficult in our patient. Although the implications of positive surgical margins remain unclear with regard to overall patient survival, surgical resection followed by radiation therapy has been shown to be optimal, as it reduces the risk of local reoccurrence.³ There have been reported cases of cutaneous angiosarcoma of the leg that were treated with amputation without signs of reoccurrence or metastasis.^10,13,14 Given the results from these cases and considering that our patient had no metastasis, amputation seemed to be a good prognostic option; however, considering other factors regarding the patient’s comorbidities and quality of life, her family decided not to pursue any further treatment with amputation or radiation therapy.

Conclusion

There should be low threshold for biopsy in patients who present with nonhealing wounds that do not progress in the normal phase of wound healing with suspicion for malignancy. As seen with our patient, cutaneous angiosarcoma can clinically mimic many disease processes, and although rare in nature, it should always be considered when a patient presents with a rapidly growing lesion in the setting of chronic lymphedema or venous ulcer.