Isolated colonic amyloidosis: a rare condition mimicking malignancy.

We report the case of a 54-year-old male with localized colonic amyloidosis presenting as rectal bleeding. Initial colonoscopy revealed a neoplastic-appearing lesion in the descending colon, but histopathology identified amyloid deposits, confirmed by Congo Red staining. Further assessment ruled out systemic involvement and primary (AL) amyloidosis, establishing the diagnosis as isolated colonic amyloidosis. This case highlights the importance of biopsy and histopathological evaluation in patients with atypical findings, especially when confounding factors such as monoclonal gammopathy of undetermined significance (MGUS) are present. Comprehensive pathological and molecular assessment are important to differentiate between localized and systemic amyloidosis and guide appropriate management.