Cortical reflex myoclonus

Abstract

Patients (3) with a type of myoclonus produced by intention and somatosensory stimulation were studied with electrophysiologic techniques. Each jerk typically affected only a few contiguous muscles; agonist and antagonist muscles were activated simultaneously with a simple electromyographic (EMG) burst lasting 10-30 ms. Cranial nerve muscles were activated in an order indicating that the signal to produce the myoclonus traveled down the brainstem. In action-induced jerks a negative transient in the EEG from the contralateral sensorimotor cortex consistently preceded the jerk with a fixed latency. In reflex-induced jerks this negative transient could be recognized as a component of the sensory evoked potential. The types of myoclonus are reviewed; this type of myoclonus is mediated in cerebral cortex and the negative transient represents a paroxysmal depolarization shift (PDS). The myoclonus may result from hyperactivity of a component of the long-latency stretch reflex.