Objective: To illustrate the presence and characteristics of functional propriospinal myoclonus with Bereitschaftspotential (BP).

Background: The etiology of propriospinal myoclonus is mostly uncertain and functional or psychogenic factors may sometimes be attributed for the development of the clinical feature. To discern between the involuntary and voluntary jerks would be difficult solely from the clinical perspective and BP is one of the potential tools for the purpose. If the jerks were involuntary, no readiness potential can be recorded prior the electromyographic (EMG) bursts and vice versa.

Methods: The patients was a 36-year-old man who developed trunk and right thigh jerks 2 months later following a fall.7 months ago. The jerks tended to be developed during sitting or lying and would be ameliorated when walking. Distracting his attention can also suppress his jerks. BP was recorded with twenty-six Ag/AgCl scalp EEG electrodes according to the International 10-20 EEG system. All electrodes were referenced to linked earlobe electrodes and the signals were filtered with a bandpass of 0.05-70 Hz (NeuroScan SynAmps). Surface EMG was recorded from the right upper rectus abdominis during both spontaneous and mimicking jerks. The recorded signals were averaged and processed for further analysis.

Results: BP can be recorded especially of the Fz, FCz, Cz, CPz and C3, CP3, which corresponding to the topographic distribution of the trunk and right leg. The BP was present during both spontaneous and mimicking jerks. It is intriguing to note that the amplitudes of spontaneous jerks were even higher than those of mimicking jerks especially at the late BP of the aforementioned electrodes. These findings strongly suggest that his jerks were voluntary instead of involuntary and functional myoclonus was diagnosed in this regard. His jerky movements disappeared 12 months later after psychogenic intervention.

Conclusions: BP is a potentially useful tool for discerning between functional myoclonus and involuntary jerks.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/bereitschaftspotential-in-a-patient-with-functional-propriospinal-myoclonus/