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The observed reduced risk of rheumatoid arthritis and osteoarthritis in patients with schizophrenia might be tied to reporting bias rather than disease-specific biology, Dr. Carl Sellgren and colleagues reported.
Data on more than 6 million people contained in the Swedish Population Register showed significantly reduced risks of both disorders, and of other musculoskeletal diseases, among schizophrenia patients, wrote Dr. Sellgren of the Karolinksa Institute, Stockholm, and his associates. Conversely, no increased risks were found among patients with bipolar disorder, despite a shared polygenic component of 68% between the two mental illnesses (Schizophr. Bull. 2014 Apr. 8 [doi:10.1093/schbul/sbu054]).
"In light of the more severe loss of function in schizophrenia and schizoaffective disorder patients in comparison to bipolar disease patients, this is compatible with differential misclassification bias in the observed inverse association between schizophrenia and rheumatoid arthritis," the researchers wrote.
Dr. Sellgren and his team were not ready to entirely scrap the possibility of some biologic link, however.
"Interestingly, we observed a significantly decreased risk for seronegative RA in children and siblings of schizophrenia probands," he said in an interview. "Correspondingly, the lowest point estimate for schizophrenia was observed in relatives of seronegative RA patients, and the lowest point estimate among schizophrenia patients was also observed for seronegative RA. Genetic causation may be present regarding the specific association between schizophrenia and seronegative RA."
Whatever the link, the study points up the importance of looking at schizophrenia patients holistically, rather than only focusing on their mental illnesses. "It appears that the more severely affected the patient is of the psychiatric disorder, the less likely is the clinician to identify a comorbid musculoskeletal disease," he said. "These data emphasize the need of assessing and being aware of nonpsychiatric symptoms in schizophrenia."
The Swedish Medical Research Council funded the study. Dr. Sellgren made no financial disclosures.
On Twitter @Alz_Gal
The observed reduced risk of rheumatoid arthritis and osteoarthritis in patients with schizophrenia might be tied to reporting bias rather than disease-specific biology, Dr. Carl Sellgren and colleagues reported.
Data on more than 6 million people contained in the Swedish Population Register showed significantly reduced risks of both disorders, and of other musculoskeletal diseases, among schizophrenia patients, wrote Dr. Sellgren of the Karolinksa Institute, Stockholm, and his associates. Conversely, no increased risks were found among patients with bipolar disorder, despite a shared polygenic component of 68% between the two mental illnesses (Schizophr. Bull. 2014 Apr. 8 [doi:10.1093/schbul/sbu054]).
"In light of the more severe loss of function in schizophrenia and schizoaffective disorder patients in comparison to bipolar disease patients, this is compatible with differential misclassification bias in the observed inverse association between schizophrenia and rheumatoid arthritis," the researchers wrote.
Dr. Sellgren and his team were not ready to entirely scrap the possibility of some biologic link, however.
"Interestingly, we observed a significantly decreased risk for seronegative RA in children and siblings of schizophrenia probands," he said in an interview. "Correspondingly, the lowest point estimate for schizophrenia was observed in relatives of seronegative RA patients, and the lowest point estimate among schizophrenia patients was also observed for seronegative RA. Genetic causation may be present regarding the specific association between schizophrenia and seronegative RA."
Whatever the link, the study points up the importance of looking at schizophrenia patients holistically, rather than only focusing on their mental illnesses. "It appears that the more severely affected the patient is of the psychiatric disorder, the less likely is the clinician to identify a comorbid musculoskeletal disease," he said. "These data emphasize the need of assessing and being aware of nonpsychiatric symptoms in schizophrenia."
The Swedish Medical Research Council funded the study. Dr. Sellgren made no financial disclosures.
On Twitter @Alz_Gal
The observed reduced risk of rheumatoid arthritis and osteoarthritis in patients with schizophrenia might be tied to reporting bias rather than disease-specific biology, Dr. Carl Sellgren and colleagues reported.
Data on more than 6 million people contained in the Swedish Population Register showed significantly reduced risks of both disorders, and of other musculoskeletal diseases, among schizophrenia patients, wrote Dr. Sellgren of the Karolinksa Institute, Stockholm, and his associates. Conversely, no increased risks were found among patients with bipolar disorder, despite a shared polygenic component of 68% between the two mental illnesses (Schizophr. Bull. 2014 Apr. 8 [doi:10.1093/schbul/sbu054]).
"In light of the more severe loss of function in schizophrenia and schizoaffective disorder patients in comparison to bipolar disease patients, this is compatible with differential misclassification bias in the observed inverse association between schizophrenia and rheumatoid arthritis," the researchers wrote.
Dr. Sellgren and his team were not ready to entirely scrap the possibility of some biologic link, however.
"Interestingly, we observed a significantly decreased risk for seronegative RA in children and siblings of schizophrenia probands," he said in an interview. "Correspondingly, the lowest point estimate for schizophrenia was observed in relatives of seronegative RA patients, and the lowest point estimate among schizophrenia patients was also observed for seronegative RA. Genetic causation may be present regarding the specific association between schizophrenia and seronegative RA."
Whatever the link, the study points up the importance of looking at schizophrenia patients holistically, rather than only focusing on their mental illnesses. "It appears that the more severely affected the patient is of the psychiatric disorder, the less likely is the clinician to identify a comorbid musculoskeletal disease," he said. "These data emphasize the need of assessing and being aware of nonpsychiatric symptoms in schizophrenia."
The Swedish Medical Research Council funded the study. Dr. Sellgren made no financial disclosures.
On Twitter @Alz_Gal
FROM SCHIZOPHRENIA BULLETIN
Major finding: The risk for RA was decreased (hazard ratio, 0.69; 95% confidence interval, 0.59-0.80) in schizophrenia, but not in bipolar disorder. These findings suggest that the risk reduction could be attributable to reporting and misclassification bias.
Data source: The review included more than 6 million people in the Swedish Population Register.
Disclosures: The Swedish Medical Research Council funded the study. Dr. Sellgren had no financial disclosures.