Objective: We investigated how clinical electrophysiological testing can help to distinguish tremor versus myoclonus.

Background: Tremor is the most common movement disorder and myoclonus its most important differential consideration. Although polymyography is recommended when clinical distinction between tremor and myoclonus is difficult, the literature indicating how polymyography can distinguish these two movement disorders is limited.

Method: We retrospectively analysed clinical and electrophysiological data from patients who had undergone polymyography (EMG + accelerometry) to diagnose their suspected tremor or myoclonus. We show the approach taken by clinical neurophysiologists at our center to distinguish tremor versus myoclonus, which includes consideration of contraction pattern, rhythm regularity, burst duration and evidence of cortical drive.

Results: We detected 773 patients in our database, of which 556 patients were ultimately diagnosed with tremor, 140 with myoclonus and 23 with a combination of tremor and myoclonus. Polymyography confirmed the presumptive diagnosis in  425 patients (55%), and led to a change of diagnosis in 278 patients (38%). Conversions between diagnoses of  tremor and myoclonus occurred most frequently between enhanced physiological tremor, essential tremor, functional tremor and cortical myoclonus.

Conclusion: Electrophysiology is a valuable tool to differentiate tremor from myoclonus. Enhanced physiological tremor, essential tremor, cortical myoclonus and functional movement disorders can be confused based on clinical examination alone and should be considered in the same differential diagnosis.
We suggest a stepwise clinical neurophysiological approach aid the diagnosis of tremor versus myoclonus.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/electrophysiological-testing-aids-the-diagnosis-of-tremor-versus-myoclonus-in-clinically-challenging-patients/