Long-term therapy of myoclonus and other neurologic disorders with L-5-hydroxytryptophan and carbidopa.

We evaluated the therapeutic effect of L-5-hydroxytryptophan (L-5HTP), the precursor of serotonin (5-hydroxytryptamine), combined with carbidopa, a peripheral decarboxylase inhibitor, in patients with intention myoclonus and examined the serotonin metabolites in spinal fluid, blood and urine before and during therapy. In 18 patients with intention myoclonus due to anoxia or other brain damage, 11 derived more than 50% overall improvement during treatment with L-5HTP and carbidopa. Spinal-fluid 5-hydroxyindoleacetic acid was 35% lower in patients with intention myoclonus than in controls (P less than 0.05). Therapy with L-5HTP and carbidopa increased the concentration of serotonin metabolites in urine and spinal fluid. We postulate that a deficiency of brain serotonin is causally related to intention myoclonus and that the therapeutic effect of L-5HTP and carbidopa may be due to the repletion of serotonin in regions of the brain where serotoninergic neurons have degenerated.