上腕の悪性軟部腫瘍との鑑別を要した木村氏病の1例

Kimura Disease of the Arm Simulating a Malignant Soft Tissue Tumor : A Case Report

　症例は53歳の男性で，20年前に左上腕に小豆大の腫瘤が出現し，4年前から急速に増大した．当院初診時，腫瘍長径が10cmと大きく，MRIでの著明な造影効果から悪性腫瘍を疑った．生検の結果，木村氏病と診断し摘出術を施行した．術後は好酸球増多と血清IgE高値が改善し，搔痒感が軽快した．本症が上肢に発生して大腫瘤を形成することは極めて稀であり，MRI画像のみでは悪性との鑑別が困難であった．搔痒感と好酸球増多を伴う四肢軟部腫瘤に対しては，本症を念頭に置いて生検を施行すべきである．

　We report a case of 53-year-old man with Kimura disease and a mass localized in the arm that simulated a malignant soft tissue tumor.

　A bean-sized tumor that the patient first noticed 20 years before had grown rapidly during the past four years and became associated with pruritus.　Because the major axis of the tumor measured 10 cm at the first examination and MRI films showed very-high-intensity with contrast enhancement, we made a diagnosis of malignant soft tissue tumor.　However, the pathological diagnosis of the open biopsy specimen was Kimura disease.　The preoperative severe eosinophilia and high serum IgE concentration improved after total excision of the tumor, and the pruritus was relieved.

　Because large masses in an extremity are very rare in Kimura disease,it is hard to make the differential diagnosis from a malignant tumor on the basis of the MRI findings alone.　If a soft tissue tumor occurs in an extremity and is associated with eosinophilia and pruritus, Kimura disease should be included in the differential diagnosis.