粘膜下腫瘍様形態を呈した直腸孤立性ALアミロイドーシスの1例

Solitary Amyloidosis of the Rectum Featuring a Submucosal Tumor causing Hematochezia, Report of a Case

要旨　患者は64歳，女性．2012年4月上旬より血便が持続するため，当科を受診した．下部消化管内視鏡検査を施行したところ，直腸Raに径約20mm大で，頂部に潰瘍を伴う発赤調で弾性硬の粘膜下腫瘍様隆起を認め，潰瘍底の一部は黄色を呈していた．腫瘤の生検病理組織検査でアミロイドーシスと診断されたため，多発性骨髄腫や悪性疾患の併発を考え，全身CT検査，PET検査，骨髄穿刺などの精査を施行したが，いずれも異常所見を認めなかった．同年5月，精査目的で内視鏡的粘膜切除（EMR）を施行し，同腫瘤を切除した．病理組織検査でAL-κアミロイドーシスと診断された．頂部に黄色を呈する潰瘍を伴った発赤調の粘膜下腫瘍を診断する際は，アミロイドーシスも鑑別診断に入れておく必要があると考えられた．

　A previously healthy 64-year-old woman presented with hematochezia upon defecation, which she first noticed at the beginning of April, 2012. Colonoscopy revealed a red-colored and congested tumor, measuring approximately 20mm in diameter, in the rectum. The exposed surface of the center of the SMT（submucosal tumor）was somewhat yellow in color and covered with fuzz. Histopathological evaluation of a biopsy specimen obtained from the SMT suggested amyloid deposition. However, other biopsy specimens of the esophagus, stomach, duodenal bulb, second portion of the duodenum, terminal ileum, and other portions of the colon revealed no amyloid deposition. Whole-body CT（computed tomography）, PET（positron emission tomography）and bone marrow aspiration revealed no abnormalities. One month later, an EMR（endoscopic mucosal resection）of the solitary amyloidosis was performed to obtain a precise diagnosis of the SMT. Immunohistopathology revealed that the entire SMT consisted of amyloid light chain kappa deposition. Amyloidosis featuring SMT is difficult to differentiate from other SMTs. This case demonstrates that it is necessary to include amyloidosis in a differential diagnosis when a SMT has yellowish features on the exposed surface of the central tumor.