Myokymia and impaired muscular relaxation with continuous motor unit activity.

Abstract

Cases (2) of the syndrome of myokymia and impaired muscular relaxation with continuous motor unit activity were studied. Both patients complained of muscle twitching, weakness, stiffness and hyperhydrosis during their illness. Myokymia was present over the entire body in both. On repetitive testing of muscle strength each patient showed initial fatigue followed by increasing strength as he continued his efforts. Both patients improved on phenytoin therapy at high blood levels. Nerve conduction velocities were decreased. Electromyograms showed continuous electrical activity at rest which persisted during sleep and spinal anesthesia, but was diminished by curare. Intravital staining with methylene blue in 1 case demonstrated sprouting and beading of motor nerve terminals with multiple innervation of muscle fibers. The neurophysiological and pathological findings in these 2 cases indicate an abnormality of peripheral nerve in this disorder.