Serotonin and myoclonus.

Biochemical studies of serotonin metabolism and a therapeutic trial of L-5-hydroxytryptophan (L-5-HTP) in combination with carbidopa were carried out in 19 patients with myoclonus. In 6 patients with intention myoclonus, the cerebrospinal fluid concentration of 5-hydroxyindoleacetic acid, a metabolite of serotonin was found to be significantly decreased. L-5-HTP with carbidopa dramatically decreased the frequency and intensity of myoclonus, particularly in those patients with a diagnosis of postanoxic intention myoclonus. The major side effects have been anorexia, nausea, vomiting, diarrhea and mental stimulation. We suggest that a deficiency of brain serotonin is causally related to myoclonic muscle movements and the therapeutic efficacy of L-5-HTP plus carbidopa may be due to the repletion of serotonin in regions of the brain where serotoninergic neurons have degenerated.