Motor neuron rigidity. An electrophysiological, pharmacological and pathological study.

A 28-year-old male with generalized muscle stiffness and widespread muscle twitching is described. Continuous electrical activity was present at rest and could be abolished only by succinylcholine, curare, and block of the distal part of the peripheral nerve. Muscle biopsy revealed mild myopathic changes. In addition glycogen depletion was found in muscle fibres which were type IIb in one region of the biopsy and type I in another. With carbamazepine treatment marked improvement occurred both clinically and electromyographically. It is concluded that the abnormal electrical activity originated in the terminal branches of the peripheral motor nerve and that this activity was confined to muscle fibres belonging to single motor unit territories.