Twenty-five-year old man suffering from paranoid psychosis was given quetiapine for persisting symptoms. He also had myoclonic disorder which has become worse just after administering quetiapine. Physical, neurological and laboratory findings were normal. He once had a generalized seizure in our clinic. The electroencephalography (EEG) revealed an epileptic focus on frontal region. He has been diagnosed as frontal lobe epilepsy exacerbated by quetiapine. He has recovered and was doing well after withdrawn the drug.

Twenty-three-year old women who had bipolar disorder was hospitalized due to a manic episode. Physical examination and routine laboratory tests were normal. Lithium at 600mg/d and quetiapine at 300 mg/d were started. Quetiapine has been gradually increased up to 900 mg/d at which the myoclonic symptoms first noted. They were disappeared after quetiapin was tapered to 600 mg/d. To control manic symptoms, quetiapine dosage had to be increased up to 700 mg/d again, but myoclonus was reappeared. Quetiapin was replaced with risperidon and manic symptoms subsided. No myoclonic seizures were noted during follow-up.

EEG abnormalities particularly likely with clozapine and olanzapine, moderate with risperidone, and the lowest with quetiapine. The risk of quetiapine-induced epilepsy was estimated as 0.75%. Evaluating of patients for the epileptic background is important in selecting proper antipsychotic medication.