Gastric mucosa-associated lymphoid tissue lymphoma diagnosed following localized gastric AL amyloidosis.

Gastrointestinal amyloidosis is a rare condition with diverse clinical and endoscopic manifestations. Among these subtypes, localized gastric AL amyloidosis is rare and associated with lymphoproliferative disorders. Here, we report a case of gastric mucosa-associated lymphoid tissue (MALT) lymphoma diagnosed during follow-up of localized gastric AL (κ) amyloidosis. A 65-year-old woman who underwent periodic endoscopic screening was found to have a localized erythematous lesion with erosion in the lower gastric body. Histopathological examination revealed amyloid deposits. Although potassium permanganate treatment suggested AA amyloidosis, immunohistochemical analysis confirmed AL (κ)-type amyloid. Systemic evaluation revealed no evidence of plasma cell dyscrasia, and localized gastric AL amyloidosis was diagnosed. After six months, the lesion regressed, but a newly identified discolored lesion was diagnosed as MALT lymphoma with plasmacytic differentiation. This case highlights the limitations of potassium permanganate-based amyloid typing and raises the possibility of an association between localized AL amyloidosis and lymphoproliferative disorders. These cases require careful endoscopic surveillance.