The
serotonin precursor L-5-hydroxytryptophan is useful
therapy for patients with posthypoxic
intention myoclonus. L-5-hydroxytryptophan plus
carbidopa was administered to eight patients with this disorder or other syndromes in which
myoclonus is prominent. This treatment (1) decreased the frequency of occurrence and amplitude of
intention myoclonus in two patients with posthypoxic
intention myoclonus and in one with idiopathic
myoclonus, (2) had no effect in one patient with congenital
encephalopathy and
myoclonus, and (3) increased the frequency of occurrence and amplitude of
myoclonus in two patients with
lipid storage disease, one with
myoclonic epilepsy, and in an additional patient with idiopathic
myoclonus. Therefore, L-5-hydroxytryptophan does not effect improvement in all forms of
myoclonus; it should be given with caution because it produces a high incidence of side effects. A patient's response to L-5-hydroxytryptophan
therapy may be important in a diagnostic classification of myoclonic syndromes based on differences in indoleamine
neurotransmitter function.