IIc型様の形態を呈した限局性直腸アミロイドーシスの1例

Localized Amyloidosis of the Rectum Presenting as a Depressed Lesion, Report of a Case

要旨●患者は70歳代，男性．内視鏡検査で直腸に異常を指摘され，当科に紹介された．直腸S状部に半周弱発赤調の比較的境界明瞭な円形の陥凹性病変を認め，NBI拡大観察では陥凹内に正常粘膜島や腺管を取り囲む血管がみられ，EUSで第1層〜第3層はほぼ均一な高エコー像を呈していた．病変からの生検でアミロイドを認めたが，直腸陥凹病変以外の消化管には認めず，心・甲状腺超音波検査や骨髄穿刺でも異常はみられなかった．免疫組織化学染色でamyloid A（−），transthyretin（−），β₂-microglobulin（−），免疫グロブリン軽鎖のκ鎖・λ鎖は判定不能であり，限局性直腸アミロイドーシス（AL型疑い）と診断し，無治療で経過観察を行っている．自験例のように直腸陥凹内のみにアミロイド沈着を認める症例は非常にまれと考えられたので報告する．

　A man in his 70s with rectal abnormalities detected on colonoscopy was referred to our hospital. A relatively well-defined, red-colored, round-shaped, depressed lesion was recognized in the rectum ; insular mucosa and blood vessels surrounding the colonic glands were observed to be normal using magnifying narrow-band imaging, and the first three layers exhibited an almost uniform high-echoic lesion on endoscopic ultrasonography. Biopsy of the lesion confirmed amyloidosis, with no amyloid deposits in the gastrointestinal tract other than those in the depressed lesion in the rectum. Cardiac and thyroid ultrasounds revealed no findings suggestive of amyloidosis, and there were no abnormal findings in the bone marrow analysis. Detection of amyloid A（−）by immunostaining, transthyretin（−）, β₂-microglobulin（−）, and an indeterminable level of κ or λ immunoglobulin light chain led to the diagnosis of localized amyloidosis in the rectum. The patient is being followed up with no intervention. Here we report a very rare case of amyloid deposits found only in a depressed lesion in the rectum.