Moving toward “laboratory‐supported” criteria for psychogenic tremor

Petra Schwingenschuh,John C Rothwell,Mark J Edwards,Stephan Seiler,Reinhold Schmidt,Tabish A Saifee,Carla Cordivari,Kailash P Bhatia,Maria Aguirregomozcorta,Petra Katschnig

doi:10.1002/mds.23922

Abstract

A confident clinical diagnosis of psychogenic tremor is often possible, but, in some cases, a “laboratory-supported” level of certainty would aid in early positive diagnosis. Various electrophysiological tests have been suggested to identify patients with psychogenic tremor, but their diagnostic reliability has never been assessed “head to head” nor compared to forms of organic tremor other than essential tremor or PD. We compared baseline tremor characteristics (e.g., frequency and amplitude) as well as electrophysiological tests previously reported to distinguish psychogenic and organic tremor in a cohort of 13 patients with psychogenic tremor and 25 patients with organic tremor, the latter including PD, essential-, dystonic-, and neuropathic tremors. We assessed between-group differences and calculated sensitivity and specificity for each test. A number of tests, including entrainment or frequency changes with tapping, pause of tremor during contralateral ballistic movements, increase in tremor amplitude with loading, presence of coherence, and tonic coactivation at tremor onset, revealed significant differences on a group level, but there was no single test with adequate sensitivity and specificity for separating the groups (33%–77% and 84%–100%, respectively). However, a combination of electrophysiological tests was able to distinguish psychogenic and organic tremor with excellent sensitivity and specificity. A laboratory-supported level of diagnostic certainty in psychogenic tremor is likely to require a battery of electrophysiological tests to provide sufficient specificity and sensitivity. Our data suggest such a battery that, if supported in a prospective study, may form the basis of laboratory-supported criteria for the diagnosis of psychogenic tremor. © 2011 Movement Disorder Society

Highlights

Tremor amplitudes in response to weighting the limb,[3,7] entrainment or an increase in variability and change of tremor frequency while tapping with the contralateral hand,[7,8,9,10] less accurate tapping performance at requested frequencies,[7] significant coherence in bilateral tremors,[11] and transient arrest of tremor during a ballistic movement of the other hand.[12]
We selected a clinically heterogeneous Psychogenic tremor (PsyT) group that included 8 patients who did not show certain clinical criteria—such as entrainability and distractibility— that would be relevant for the outcome of some of the electrophysiological tests, but in whom diagnosis was based on other criteria, such as presence of further somatizations and placebo response
A repeated-measures analysis of variance (ANOVA) showed a significant interaction of loading and group (F(1,36) 1⁄4 4.69, P 1⁄4 0.037) and a significant effect of group (F(1,36) 1⁄4 5.17, P 1⁄4 0.029), which was explained by a significant increase of tremor amplitude (TP) with loading in PsyT, compared to organic tremor (OrgT)

Summary

Introduction

Tremor amplitudes in response to weighting the limb,[3,7] entrainment or an increase in variability and change of tremor frequency while tapping with the contralateral hand,[7,8,9,10] less accurate tapping performance at requested frequencies,[7] significant coherence in bilateral tremors,[11] and transient arrest of tremor during a ballistic movement of the other hand.[12]. Current data, using such tests to distinguish between PsyT and OrgT, have two important limitations. We consider this study a first step toward the development of laboratorysupported criteria for PsyT

Methods

Results

Discussion

Conclusion