Drug-induced myoclonus: frequency, mechanisms and management

Olanzapine-Induced Myoclonic Status

Olanzapine-related seizures have rarely been reported despite its proconvulsant risk. This is the first description of myoclonic status induced by this antipsychotic. A 54-year-old woman with probable Alzheimer disease developed continuous myoclonic jerks just after adding olanzapine for neuropsychiatric symptoms. She was already receiving citalopram and donepezil at low doses. Jerks coincided with spikes and polyspike/wave complexes on EEG. Olanzapine was immediately suspended and the seizures subsided. A control EEG showed no paroxysmal discharges. Several months later she was given haloperidol and she remained seizure free. Olanzapine shares some pharmacologic similarities with clozapine, a neuroleptic with a high risk of dose-dependent seizures. This adverse effect should be taken into account, and olanzapine should be used with caution if concomitant circumstances could decrease the seizure threshold.