Objective: The aim of the study was to determine if home-monitoring of surface electromyography (EMG) can be used to detect silent periods of muscle activity related to negative myoclonia.

Background: Progressive myoclonic epilepsy type 1 (EPM1, Unverricht-Lundborg disease) is a neurodegenerative disorder.  One of the symptoms of EPM1 is negative myoclonus, that is characterized as a sudden loss of muscle tonus. The EMG equivalent of negative myoclonus is a silent period of muscle activity with a duration from 50 to 300 ms. Clinical assessment of negative myoclonus is performed by video-recorded Unified Myoclonus Rating Scale (UMRS) examination. Negative myoclonus severity is scored from 0 to 3 through visual inspection by an expert.

Method: Surface EMG was recorded from N = 23 patients from both upper limbs of the patient: biceps brachii of the dominant arm and extensor digitorum communis of the non-dominant arm. Surface EMG was recorded at home for over 48 hours and the data of 23 subjects were used for the analysis. The principle of the algorithm was as follows: (1) If the difference in amplitude between two consecutive datapoints was larger than the preset threshold, a marker was placed to represent a possible silent period. (2) Silent period was accepted if its length was between 70ms and 230ms (The length criterion was based on visual inspection of the data beforehand). (3) Muscle activity before and after the silent period was assessed with a moving average filtered signal. If muscle activity was larger than a preset threshold before and after silent period, it was accepted. (4) Finally, if two silent periods appeared inside a 1 second window, both were disqualified. This criterion was based on visual inspection of the data, to rule out other myoclonic events or tremor-like activity. All thresholds were experimentally obtained.

Results: None of the patients had myoclonus severity above 2. Algorithm found more and longer silent periods from patients with a negative myoclonus severity of 2 than from other patients. Even patients with severity score of 0 in the clinic seemed to have silent periods of muscle activity based on the home measurements.

Conclusion: Negative myoclonus is challenging to detect and evaluate clinically. Surface EMG can be used to detect silent periods related to negative myoclonus and the method is usable for long-term home-monitoring.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/detection-of-silent-periods-of-muscle-activity-related-to-negative-myoclonia/