Localized Rectal Amyloidosis with Morphologic Changes from the Submucosal Tumor to the Ulcerative Lesion That Led to Hematochezia During Observation

A 75-year-old woman visited our hospital with constipation. Colonoscopy revealed a submucosal tumor in the rectum. She was followed up as a case of mucosal prolapse syndrome. Six years later, she was referred to our hospital due to hematochezia and abdominal pain. Colonoscopy revealed that the submucosal tumor had an ulcerative appearance with bleeding. Low anterior resection was performed. Amyloid protein deposition was detected from the submucosa to subserosa. Other organs showed no evidence of amyloidosis; we therefore diagnosed the patient with localized rectal amyloidosis. This is a rare case of symptomatic localized rectal amyloidosis whose long-term progression was able to be endoscopically observed.