嚢胞状リンパ節転移を伴った爪床のpigmented epithelioid melanocytoma

・嚢胞状リンパ節転移を伴った爪床のpigmented epithelioid melanocytoma（PEM）と考えられたまれな症例を経験した．

・病理組織所見は表皮内に腫瘍細胞はみられず，真皮にメラニンを豊富に有する類円形の細胞と紡錘形の細胞が密に増殖しており，大量のメラニン顆粒のため核／細胞異型の判断が困難であり診断に苦慮した．

・メラニンを豊富に伴った細胞増殖が主体であったため，DAB（diaminobenzidine）発色法による免疫染色を施行する前に過酸化水素法によるメラニン脱色法を用いた．

（「症例のポイント」より）

　

A case of pigmented epithelioid melanocytoma on the nail bed with cystic lymph node metastasis

　

Tohgi, Natsuko1）Masuzawa, Mamiko1）Kounoike, Natsuko2）Amoh, Yasuyuki1） 1）Department of Dermatology, Kitasato University School of Medicine 2）Department of Plastic and reconstructive surgery, Kitasato University School of Medicine

　

A 70-year-old Japanese man had medical histories of maxillary sinus carcinoma, renal cell carcinoma and colon carcinoma, and an enlarged right axillary lymph node was observed by the follow-up computed tomography scan. Histopathological examination of the lymph node revealed its cystic structure and tumor cells with abundant melanin were proliferated in the cyst wall. Therefore, the lymph node was suspected as a metastasis of malignant melanoma. As a primary lesion, a black blue nodule with nail destruction was observed on subungual area of his right thumb. The histopathological findings of the subungual lesion showed spindle and epithelioid tumor cells with heavy pigmentation in only dermis. The tumor cells showed no mitotic activity and accompanied with plenty of melanophages, and necrotic change was not observed in the primary site. Hence, we diagnosed it as pigmented epithelioid melanocytoma with cystic lymph-node metastasis.