Facial myokymia in multiple system atrophy.

Two patients are described with clinical and neuroimaging features consistent with a diagnosis of multiple system atrophy (MSA). The patients are unusual in that facial myokymia became apparent clinically at some stage in their illness. In each patient, the nature and severity of the involuntary facial movements evolved over the course of the illness. Electrophysiologically the movement pattern was consistent with myokymia, and studies of blink-reflex responses suggested that the myokymic discharges were of brainstem origin. Involuntary facial movements described as facial action myoclonus with electrical characteristics consistent with myoclonus have been described previously in hereditary olivopontocerebellar atrophy (OPCA). Our report describes electrical and clinical features of facial myokymia in MSA with electrical features suggesting hyperexcitability of the facial motorneurons in the brainstem. Such myokymic movements may occur more frequently in MSA than previously recognised but may be missed clinically because of their evolving nature.