Phenytoin-induced hyperkinesia.

Previously described cases of phenytoin-induced hyperkinesia are reviewed. Three new cases are reported, in one of which hyperkinesia persisted for 5 years, although serum phenytoin on several occasions was in the therapeutic range. Similarities between phenytoin-induced hyperkinesia and hyperkinesia in Huntington's chorea and in neuroleptic- and L-DOPA-treated patients are discussed. It is pointed out that the frequency of organic cerebral damage seems to be high among patients with phenytoin-induced hyperkinesia. The hypothesis is presented that phenytoin induces hyperkinesia by increasing dopaminergic and serotonergic activity in the basal ganglia, and that patients with preexisting basal ganglia damage are the most susceptible.