視神経炎との鑑別に苦慮したレーベル遺伝性視神経症の1例

A case of Leber's hereditary optic neuropathy differentiate from optic neuritis

要約　目的：視神経炎との鑑別に苦慮したレーベル遺伝性視神経症の報告。

症例：14歳，男児。2022年12月から左眼の視力低下を自覚し，当院を紹介され受診となった。視力は右（1.0），左（0.1），眼圧は左15mmHg，前眼部，中間透光体，眼底に異常所見はなかった。相対的瞳孔求心路障害は陰性，平均限界フリッカ値左15Hzと低下，フルオレセイン蛍光眼底造影検査では両視神経乳頭からの蛍光色素漏出を認めなかった。動的視野検査では左眼の中心暗点を認めた。頭部単純MRIでは左視神経高信号を認め，左球後視神経炎と診断した。初診から約1か月よりステロイドパルス療法を施行，その3日目より徐々に右眼視力低下も自覚し，両眼中心暗点が出現した。治療反応に乏しかったため，ステロイドパルス療法2クール目を施行。その後も改善がなかったため，血漿吸着療法を4日施行，さらに免疫グロブリン大量静注療法を5日間施行した。治療抵抗性のため遺伝子検査を施行し，ミトコンドリア遺伝子11778変異を認め，レーベル遺伝性視神経症と診断した。現在，コエンザイムQ10製剤とビタミン療法を行っており，初診から9か月経過した現在，視力は右（0.5），左（0.4p）にて両眼中心暗点は残存している。

結論：小児視神経炎とレーベル遺伝性視神経症は臨床経過が類似している。今回，眼底所見や頭部MRIが非典型的であった点で診断に苦慮し，最終的に筆者らはミトコンドリア遺伝子検査にて確定した。

Abstract　Purpose：We report a case of Leber's hereditary optic neuropathy, which differentiates from optic neuritis.

Case：A 14-year-old man presented with blurring of vision in the left eyes in December 2022 and was referred to our hospital. At the first visit, corrected visual acuity was 0.1 in the left eye. Intraocular pressure was 15 mmHg in the left eye. No abnormal findings were observed from the anterior eye to the fundus. The relative afferent pupillary defect was negative in both eyes. The critical fusion frequency was 15 Hz in the left eye. Fluorescein angiography revealed no leakage of the bilateral optic disc. Goldman perimetry revealed a central scotoma in the left eye, therefore we diagnosed retrobulbar optic neuritis.

Steroid pulse therapy was administered about a month after the first visit, and from the third day on, he gradually became aware of a decrease in vision in his right eye, and a central scotoma appeared in both eyes. Due to the poor treatment response, steroid pulse therapy was administered on the second day. With no improvement obesrved, plasma adsorption therapy was administered for 4 days, and intravenous immunoglobulin（IVIG）was administered for 5 days. Genetic testing was performed for treatment resistance, and mitochondrial gene mutations were found. Currently, he is on coenzyme Q10 preparations and vitamin therapy, and as of 9 months after his first visit, he has a residual central scotoma in both eyes with visual acuity, and corrected visual acuity was 0.5 in the right eye and 0.4p in the left eye.

Conclusion：Pediatric optic neuritis and Leber's optic neuropathy have a similar clinical course. This time, Fundus findings and an MRI made the diagnosis difficult. It was finally confirmed by mitochondrial genetic testing.