Distinguishing psychogenic and essential tremor.

In contrast to essential tremor (ET), psychogenic tremor (PT) is often manifested by shaking with variable amplitude and frequency, distractibility, suggestibility, and entrainment. The sensitivity and specificity of these findings in differentiating PT and ET have not been systematically examined. In order to determine clinical features that reliably distinguish PT from ET, we collected patient information regarding tremor onset, spontaneous remissions, family history, and employment history. A "blinded" rater evaluated video segments of subjects using a standardized protocol with special attention to distractibility, suggestibility, or entrainment. A total of 45 subjects with ET or PT were enrolled in this study: 33 met clinical criteria for ET with a mean age of 56.8+/-17.0 years and 12 met clinical criteria for PT with a mean age of 42.5+/-11.0 years. PT subjects were significantly more likely to relay a history of sudden onset (p=0.03), spontaneous remissions (p=0.03), and shorter duration of tremor (p=0.001). Family history of tremor was significantly more common in the ET group (p=0.001). A moderate-to-marked degree of distraction with alternate finger tapping (p=0.01) and mental concentration on serial 7 s (p=0.01) was more common in PT. Furthermore, suggestibility with a tuning fork (p=0.04) and exacerbation with hyperventilation (p=0.06) seemed predictive of PT. Entrainment was not different in the two groups. In conclusion, a history of tremor with sudden onset and spontaneous remissions along with distractibility and suggestibility on examination are good predictors of PT and help differentiate it from ET.