Distinguishing psychogenic and essential tremor

Abstract

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.

Introduction

The most common cause of tremor, affecting up to 5% of people over the age of 65, is essential tremor (ET) characterized by a progressive 4–12 Hz postural and kinetic tremor [1], [2]. Ninety percent of cases involve the hands; additional affected areas include the head, voice, legs, and tongue. Over time, patients tend to exhibit a lower frequency tremor with larger amplitude and poorer response to medications, leading to more disability [3]. Psychogenic movement disorders (PMD) comprise 4.1% of all patients seen in our movement disorders clinic [4], [5]. PMD can be challenging to properly diagnose [6], [7] given the potential for complex phenomenology including dystonia, [8], [9] myoclonus, [10] tics, [11] hemifacial spasm, [12] parkinsonism, [13], [14] paroxysmal dyskinesia, [15] palatal tremor, [16], [17] and gait dysfunction [18]. Psychogenic tremor (PT) is the most common PMD, accounting for about 25% of all cases [4]. Physical examination techniques such as entrainment, distraction, and suggestibility have been used to aid differentiation of PT from organic tremors such as ET. Electrophysiological studies are also used, but rarely accessible to practitioners. The primary aim of this study is to determine which clinical features most reliably facilitate the diagnosis of PT and help clinicians differentiate this PMD from ET.