Syndrome of continuous muscle-fiber activity: increased CSF GABA and effect of dantrolene.

In a patient with a syndrome of continuous muscle fiber activity, peripheral nerve block completely abolished the EMG discharges. Reduction of spontaneous discharges by epidural block and demonstration of a silent period after the H response suggested that the disorder may originate in the spinal cord or ventral roots, sparing inhibitory influences on the alpha-motoneuron to some extent. GABA (gamma-aminobutyric acid) content in CSF was remarkably increased. Therapeutically, dantrolene sodium was as effective as phenytoin or carbamazepine.