Muscle cramp as the result of impaired GABA function--an electrophysiological and pharmacological observation

We investigated the mechanism of cramps in 2 patients: a 48-year-old man with bulbospinal neuronopathy, and a 46-year-old man with amyotrophic lateral sclerosis. Cramps were quite easily induced by volitional exertion and high-frequency stimulation of the peripheral nerves. When an ulnar nerve was blocked with lidocaine at the elbow, no cramp was induced despite the application of high-frequency stimulation at the wrist. Diazepam (GABAA agonist) was effective in the first patient and baclofen (GABAB agonist) in the second, with no cramps induced in spite of increasing stimulation intensity. Impairment of interneurons mediated by GABA as the neurotransmitter is thought to be involved in the mechanism of the cramps.