診断に苦慮した悪性黒色腫関連網膜症の1例

A case of melanoma-associated retinopathy with difficult diagnosis

要約　目的：悪性黒色腫関連網膜症（MAR）の本邦での報告は稀である。今回，経過中に片眼の陰性b波が両眼の陰性b波に変化した症例を経験したので報告する。

症例：58歳，男性。1週間前より右眼の霧視，夜間の羞明，光視症を主訴に近医を受診。原因精査目的に当院を紹介され受診となった。既往歴はなし。初診時の矯正視力は両眼1.0，細隙灯顕微鏡検査では異常所見はなく，眼底も検眼鏡では異常を認められなかった。

所見：蛍光眼底造影検査では症状に関係する明らかな異常所見は認めず，動的視野検査においては右眼にマリオット盲点の拡大がみられた。電気学的検査では，多局所網膜電図（ERG）では症状のある右眼ではなく左眼に振幅低下がみられ，全視野ERGでは右眼に陰性b波がみられた。症状を説明できる所見が得られなかったため，改めて本人に病歴聴取を行ったところ寛解状態である足底部悪性黒色腫の既往があることがわかった。皮膚科に再精査を依頼したところ，悪性黒色腫の肺転移が見つかり，臨床的にMARと診断した。その後，経過中に右眼のみに生じていた陰性b波が左眼にも生じた。

結論：悪性黒色腫の病歴聴取ができなかった場合でも，ERGにて片眼の陰性b波を認めた際には，MARを鑑別する必要がある。

Abstract　Purpose：Malignant melanoma-associated retinopathy is rarely reported in Japan. We report a case in which a negative b-wave in one eye changed to a negative b-wave in both eyes during the course of the disease.

Case：A 58-year-old man visited his ophthalmologist at local clinic one week ago with complaints of foggy vision in the right eye, photophobia at night, and a flickering sensation in the right eye. One week later, he was referred to our hospital for a thorough examination of the cause. He had no previous medical history. At the time of initial examination, his corrected visual acuity was 1.0 in both eyes, slit-lamp microscopy revealed no abnormalities, and ophthalmoscopy revealed no abnormalities in the fundus.

Findings：Fluorescence angiography revealed no obvious abnormalities related to symptoms, and dynamic visual field testing showed an enlarged Mariotte blind spot in the right eye. A multifocal electroretinogram showed decreased amplitude in the left eye, but not in the symptomatic right eye. A full-field electroretinogram showed a negative b-wave in the right eye. The left eye was subnormal. Since there were no findings that explained the symptoms, we asked the patient about his medical history. He had a plantar malignant melanoma, in remission, which he had not initially reported. After making inquiries at the other hospital, the patient was found to have pulmonary metastasis of malignant melanoma and was clinically diagnosed with malignant melanoma-related retinopathy. Subsequently, during the course of the disease, a negative b-wave, which was initially present only in the right eye, had also developed in the left eye.

Conclusion：Even when it is impossible to obtain a history of malignant melanoma, it is necessary to identify malignant melanoma-associated retinopathy when a negative b-wave is detected in one eye on electroretinogram.