We used abdominal ultrasonography to examine a 65-year-old man who had abdominal pain after being admitted to this
institution because of dermatomyositis. The examination showed the wall of the sigmoid colon to be diffusely thickened
(maximum 7.8 mm). The layer between the mucosa (M) and the submucosa (SM) was blurred, but the layer between the SM
and the muscularis propriae (MP) was distinct, and compressibility (degree to which the wall was compressed by the probe)
was decreased. We thus suspected diffusely infiltrating sigmoid carcinoma. A barium-enema roentogenograph showed long-drawn stenosis and tapering margin in the sigmoid colon. Colonoendoscopy showed erosive and reddish mucosa and stenosis in
the sigmoid colon. The biopsy revealed poorly differentiated adenocarcinoma. Diffusely infiltrating sigmoid carcinoma was
confirmed on autopsy.