Identification of psychogenic, dystonic, and other organic tremors by a coherence entrainment test

Abstract

The differentiation of psychogenic from organic tremors, particularly those of a dystonic nature, can be difficult on clinical grounds. Entrainment of tremulous movements of different body parts into a single rhythm has been used clinically as a means of distinguishing these tremor forms, based on the inability of a patient with hysterical tremor to generate voluntary tapping oscillations independent of their ongoing tremor oscillation. The coherence entrainment test is a quantified electrophysiological entrainment test performed on accelerometer or surface EMG tremor signals. This test was carried out on 25 patients referred with suspected psychogenic tremor or dystonic tremor and on 10 normal subjects attempting to tap two independent voluntary oscillations. Using established and new clinical diagnostic criteria, patients were assigned the following final clinical diagnoses: 6 cases of clinically definite dystonic tremor, 5 cases of probable dystonic tremor, 2 cases of classic essential tremor, 5 cases of clinically definite psychogenic tremor, 3 cases of probable psychogenic tremor and 4 uncertain cases. On comparing these clinical diagnoses with those reached by a coherence entrainment test subsequently carried out on each patient, there was 100% concordance in both clinically definite and clinically probable patients. In uncertain cases, when later clinical information came to light, this also corroborated with the coherence entrainment diagnosis. No normal subjects were able to "mimic" organic tremor. The coherence entrainment test appears to be a sensitive and specific means of distinguishing psychogenic tremor from dystonic and other organic tremors.

Psychogenic palatal tremor

“…In addition to the spectral analysis, a coherence entrainment analysis was performed between the EMG oscillations recorded from her hand tapping and the activity from the neck accelerometer channel. 6 This test has been shown recently to be a sensitive and specific analytic tool for distinguishing between psychogenic tremor and organic tremor. 6 Accelerometer-EMG coherence was present when two consecutive bins on the coherence plot rose above the 95% confidence limit for the plot.…”

“…6 This test has been shown recently to be a sensitive and specific analytic tool for distinguishing between psychogenic tremor and organic tremor. 6 Accelerometer-EMG coherence was present when two consecutive bins on the coherence plot rose above the 95% confidence limit for the plot. Coherence was seen in the 1.5 Hz, 1.7 Hz, 2.0 Hz, and 3.5 Hz conditions (Fig.…”

Psychogenic Movement Disorders

“…On the other hand, organic tremor usually has slightly different frequencies in different body parts. A quantified electrophysiological entrainment test performed on accelerometer or surface EMG tremor signals may provide supportive evidence of a functional tremor (McAuley & Rothwell 2004). Recently, Czarnecki and colleagues revealed distinct patterns of cerebral perfusion, during rest and motor task, as measured by SPECT that distinguish psychogenic tremor from essential tremor and controls (Czarnecki et al 2011).…”

Dystonia with Tremors: A Clinical Approach

“…A psychogenic tremor can be confused with a dystonic tremor since the duration of the tremor burst in the dystonic tremor is widely variable reflecting its jerky nature and is similar to some psychogenic tremors (McAuley and Rothwell, 2004). However, the psychogenic tremor has psychogenic signs, multiple somatizations, secondary gain, or is related to an injury or event (Elble, 2000).…”