[Case of juvenile myoclonic epilepsy misdiagnosed as simple partial seizure for more than 60 years].

A 77-years-old woman was admitted to our hospital due to uncontrolled myoclonus and generalized seizure. Since the age of 17, she has been suffering from myoclonic jerks and partial convulsions in her right arm. Administration of several unknown anticonvulsants had not alleviated her condition. She was able to spend her life without a handicap, except for the symptoms described above. She has been experiencing psychological stress since the age of 50, which has resulted in worsening of her symptoms, and she was prescribed phenytoin, carbamazepine, and phenobarbital, which were also ineffective. When a generalized convulsive attack occurs, she shows rapid muscle twitches in her right arm and her consciousness is clear. She also has cerebellar ataxia in her extremities. Brain magnetic resonance imaging (MRI) showed obvious cerebellar atrophy, and an electroencephalogram revealed a diffuse spike and wave complexes. A surface electromyogram (EMG) confirmed myoclonus in both arms. We diagnosed her as having juvenile myoclonus epilepsy and initiated sodium valproate monotherapy, which relieved the symptoms. The observed cerebellar ataxia might be due to long-term administration of phenytoin. When a neurologist encounters an intractable seizure without loss of consciousness, surface EMG is useful for diagnosing this treatable disease.