短期間に左右の同名半盲が交互に観察されたミトコンドリア脳筋症の1例

A case of mitochondrial encephalomyopathy with transient homonymous hemianopia that recurred alternately on the left and right eye

要約　目的：脳卒中様発作を契機として，一過性の同名半盲を左右交互に生じたミトコンドリア脳筋症・乳酸アシドーシス・脳卒中様発作症候群（MELAS）の症例報告。

症例：14歳，男児。痙攣と意識障害を主訴に当院小児科を受診した。経過観察により症状は軽快したが，その2か月後に発熱，頭痛，左視野障害が出現し，小児科から眼科へ紹介となった。

所見：矯正視力は両眼ともに1.2で，前眼部，中間透光体，眼底に異常はなかったが，視野検査で左同名半盲を認めた。頭部MRIで右後頭葉に異常信号を，血液検査や髄液検査で乳酸値の上昇を，さらにミトコンドリア遺伝子検査でA3243G変異を認めたことから，MELASと診断された。加療後に症状は軽快し退院となったが，その2か月後に頭痛，右視野欠損のため小児科を再度受診し，入院となった。頭部MRIで今度は左後頭葉の異常信号を呈し，右同名半盲を認めた。小児科で前回と同様の治療を行ったところ，症状が改善したため退院となり，2か月後の当科再診時には両眼とも同名半盲は消失していた。

結論：MELASでは，頭蓋内病変の部位の変化によりさまざまな視野障害を呈することがあるため，慎重な経過観察を要する。

Abstract　Purpose：To report a case of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes（MELAS）with transient homonymous hemianopia that recurred alternately on the left and right eye.

Case：A 14-year-old boy visited the pediatrics department of our hospital with complaints of convulsions and impaired consciousness. Two months later, he was referred to the department of ophthalmology due to complaints of left visual field defect.

Findings：Best corrected visual acuity was 1.2 in both eyes with no specific. Goldmann perimetry confirmed left homonymous hemianopia. An abnormal signal in the right occipital lobe on MRI, elevated lactate levels in the patient's cerebrospinal fluid and blood, and the mitochondrial genetic test that revealed A3243G mutation, together led to a diagnosis of MELAS. He recovered after treatment；however, two months later, he visited the pediatric department again complaining of headache and right visual field defect. The MRI revealed an abnormal signal in the left parietal lobe this time, and Goldmann perimetry showed right homonymous hemianopia. His condition improved progressively following medical treatment. When he visited our department two months later, his visual field was normal and radiological abnormalities had disappeared.

Conclusion：MELAS may present reversible various visual field defects depending on the site of the intracranial lesion；thus, careful follow-up is required.