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A new tool called the tremor stability index (TSI) can aid the differential diagnosis of essential tremor and Parkinson’s disease, according to research published online ahead of print April 27 in Brain. The TSI has a diagnostic accuracy of approximately 90% for these syndromes, and neurologists can derive it from brief, inexpensive, and noninvasive tremor recordings.
Misdiagnosis of tremor syndromes is common and affects clinical care and research. The current gold standard for diagnosis is clinical evaluation by a specialist in movement disorders. In 2015, Brittain et al found that the frequency of tremor remains stable over a narrow range of frequencies in essential tremor, but remains stable over a broader range in Parkinson’s disease. 
Lazzaro di Biase, PhD, a postdoctoral researcher at Università Campus Bio-Medico in Rome, and colleagues analyzed the overall tremor stability characteristics of essential tremor and Parkinson’s disease to develop the TSI, an interquartile range of the change in tremor frequency. The investigators performed kinematic measurements on a test cohort of 16 patients with tremor-dominant Parkinson’s disease and 20 patients with essential tremor. Data were collected after overnight withdrawal of medications. A validation cohort included new and original data taken from published studies and encompassed 42 rest tremor recordings of patients with Parkinson’s disease and eight postural tremor recordings of patients with essential tremor.
In the test cohort, Dr. di Biase and colleagues found no difference in mean instantaneous frequency between patient groups, but saw a difference in TSI between groups. For every unit increase in TSI, the odds of a patient having a diagnosis of essential tremor increased by a factor of 14.8. The optimal TSI threshold in the test cohort was 1.05; TSI values greater than 1.05 indicated a diagnosis of essential tremor, and TSI values of 1.05 or less indicated a diagnosis of Parkinson’s disease. Follow-up recordings made one year and seven months later confirmed the stability of the TSI over time for patients with Parkinson’s disease.
The investigators found a difference in mean instantaneous frequency between groups in the validation cohort, as well as a significant difference in TSI between essential tremor and Parkinson’s disease. For every unit increase in TSI, the odds of a patient having a diagnosis of essential tremor increased by a factor of 5.7. When the researchers applied the threshold of 1.05, they found that the TSI had excellent discriminatory ability. In addition, bootstrap analysis revealed that the TSI outperformed the mean harmonic power of postural tremor harmonics 72% of the time.
The TSI was robust when applied to various patient groups with differing demographics and clinical characteristics. The devices used to record tremor did not affect the TSI’s reliability, nor did postural context. According to the researchers, the TSI can be rapidly estimated from 10-second recordings of tremor.
“The TSI provides a promising diagnostic aid in clinical practice and could be a useful tool to avoid selection errors in clinical trials,” said Dr. di Biase. “It will be important to see if this index can also distinguish dystonic tremor, which may masquerade as Parkinson’s disease or essential tremor,” he added.
—Erik Greb
Suggested Reading
di Biase L, Brittain JS, Shah SA, et al. Tremor stability index: a new tool for differential diagnosis in tremor syndromes. Brain. 2017 Apr 27 [Epub ahead of print].
A new tool called the tremor stability index (TSI) can aid the differential diagnosis of essential tremor and Parkinson’s disease, according to research published online ahead of print April 27 in Brain. The TSI has a diagnostic accuracy of approximately 90% for these syndromes, and neurologists can derive it from brief, inexpensive, and noninvasive tremor recordings.
Misdiagnosis of tremor syndromes is common and affects clinical care and research. The current gold standard for diagnosis is clinical evaluation by a specialist in movement disorders. In 2015, Brittain et al found that the frequency of tremor remains stable over a narrow range of frequencies in essential tremor, but remains stable over a broader range in Parkinson’s disease.
Lazzaro di Biase, PhD, a postdoctoral researcher at Università Campus Bio-Medico in Rome, and colleagues analyzed the overall tremor stability characteristics of essential tremor and Parkinson’s disease to develop the TSI, an interquartile range of the change in tremor frequency. The investigators performed kinematic measurements on a test cohort of 16 patients with tremor-dominant Parkinson’s disease and 20 patients with essential tremor. Data were collected after overnight withdrawal of medications. A validation cohort included new and original data taken from published studies and encompassed 42 rest tremor recordings of patients with Parkinson’s disease and eight postural tremor recordings of patients with essential tremor.
In the test cohort, Dr. di Biase and colleagues found no difference in mean instantaneous frequency between patient groups, but saw a difference in TSI between groups. For every unit increase in TSI, the odds of a patient having a diagnosis of essential tremor increased by a factor of 14.8. The optimal TSI threshold in the test cohort was 1.05; TSI values greater than 1.05 indicated a diagnosis of essential tremor, and TSI values of 1.05 or less indicated a diagnosis of Parkinson’s disease. Follow-up recordings made one year and seven months later confirmed the stability of the TSI over time for patients with Parkinson’s disease.
The investigators found a difference in mean instantaneous frequency between groups in the validation cohort, as well as a significant difference in TSI between essential tremor and Parkinson’s disease. For every unit increase in TSI, the odds of a patient having a diagnosis of essential tremor increased by a factor of 5.7. When the researchers applied the threshold of 1.05, they found that the TSI had excellent discriminatory ability. In addition, bootstrap analysis revealed that the TSI outperformed the mean harmonic power of postural tremor harmonics 72% of the time.
The TSI was robust when applied to various patient groups with differing demographics and clinical characteristics. The devices used to record tremor did not affect the TSI’s reliability, nor did postural context. According to the researchers, the TSI can be rapidly estimated from 10-second recordings of tremor.
“The TSI provides a promising diagnostic aid in clinical practice and could be a useful tool to avoid selection errors in clinical trials,” said Dr. di Biase. “It will be important to see if this index can also distinguish dystonic tremor, which may masquerade as Parkinson’s disease or essential tremor,” he added.
—Erik Greb
Suggested Reading
di Biase L, Brittain JS, Shah SA, et al. Tremor stability index: a new tool for differential diagnosis in tremor syndromes. Brain. 2017 Apr 27 [Epub ahead of print].
A new tool called the tremor stability index (TSI) can aid the differential diagnosis of essential tremor and Parkinson’s disease, according to research published online ahead of print April 27 in Brain. The TSI has a diagnostic accuracy of approximately 90% for these syndromes, and neurologists can derive it from brief, inexpensive, and noninvasive tremor recordings.
Misdiagnosis of tremor syndromes is common and affects clinical care and research. The current gold standard for diagnosis is clinical evaluation by a specialist in movement disorders. In 2015, Brittain et al found that the frequency of tremor remains stable over a narrow range of frequencies in essential tremor, but remains stable over a broader range in Parkinson’s disease.
Lazzaro di Biase, PhD, a postdoctoral researcher at Università Campus Bio-Medico in Rome, and colleagues analyzed the overall tremor stability characteristics of essential tremor and Parkinson’s disease to develop the TSI, an interquartile range of the change in tremor frequency. The investigators performed kinematic measurements on a test cohort of 16 patients with tremor-dominant Parkinson’s disease and 20 patients with essential tremor. Data were collected after overnight withdrawal of medications. A validation cohort included new and original data taken from published studies and encompassed 42 rest tremor recordings of patients with Parkinson’s disease and eight postural tremor recordings of patients with essential tremor.
In the test cohort, Dr. di Biase and colleagues found no difference in mean instantaneous frequency between patient groups, but saw a difference in TSI between groups. For every unit increase in TSI, the odds of a patient having a diagnosis of essential tremor increased by a factor of 14.8. The optimal TSI threshold in the test cohort was 1.05; TSI values greater than 1.05 indicated a diagnosis of essential tremor, and TSI values of 1.05 or less indicated a diagnosis of Parkinson’s disease. Follow-up recordings made one year and seven months later confirmed the stability of the TSI over time for patients with Parkinson’s disease.
The investigators found a difference in mean instantaneous frequency between groups in the validation cohort, as well as a significant difference in TSI between essential tremor and Parkinson’s disease. For every unit increase in TSI, the odds of a patient having a diagnosis of essential tremor increased by a factor of 5.7. When the researchers applied the threshold of 1.05, they found that the TSI had excellent discriminatory ability. In addition, bootstrap analysis revealed that the TSI outperformed the mean harmonic power of postural tremor harmonics 72% of the time.
The TSI was robust when applied to various patient groups with differing demographics and clinical characteristics. The devices used to record tremor did not affect the TSI’s reliability, nor did postural context. According to the researchers, the TSI can be rapidly estimated from 10-second recordings of tremor.
“The TSI provides a promising diagnostic aid in clinical practice and could be a useful tool to avoid selection errors in clinical trials,” said Dr. di Biase. “It will be important to see if this index can also distinguish dystonic tremor, which may masquerade as Parkinson’s disease or essential tremor,” he added.
—Erik Greb
Suggested Reading
di Biase L, Brittain JS, Shah SA, et al. Tremor stability index: a new tool for differential diagnosis in tremor syndromes. Brain. 2017 Apr 27 [Epub ahead of print].