長期にわたって単純部分発作として治療され，経過中に小脳失調をきたした若年ミオクロニーてんかんの1例

A Case of Juvenile Myoclonic Epilepsy Misdiagnosed as Simple Partial Seizure for More than 60 Years

はじめに

　若年ミオクロニーてんかん（juvenile myoclonic epilepsy：JME)^1－3）は，1989年にInternational League Against Epilepsy（ILAE）に提唱された全般性てんかん症候群の1つ^4）で，思春期頃に発症し短時間のすばやいミオクローヌスを発作型とし（ミオクロニー発作），全般強直間代痙攣を伴うが意識は保たれる。発作間欠期には神経学的異常所見はなく，治療はバルプロ酸ナトリウム（VPA）が第1選択薬^{6，9，11）}であり，良好に反応し予後はよいとされる。 　今回われわれは17歳で発症し，単純部分発作として治療されていたが，発症60年後の77歳にして初めて若年ミオクロニーてんかんと診断され，VPAが著効した1例を経験した。本例では小脳失調，小脳萎縮を呈していた。フェニトイン（PHT）長期服用の副作用が疑われた。本疾患を発症早期から的確に診断することはてんかんのコントロール，薬剤の副作用防止のため重要と考え，文献的考察を加えて報告する。

Abstract

　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. (Received: January 18,2008,Accepted: August 29,2008)