This is a case of a 61-year-old woman with rheumatoid arthritis who was treated with methotrexate and prednisolone. She visited our outpatient department due to diarrhea and vomiting that lasted for one month and was admitted with a diagnosis of gastroenteritis. Upper gastrointestinal endoscopic examination revealed erythema, erosions, and granular mucosa in the duodenum. Duodenal biopsy revealed amyloid deposition, leading to a diagnosis of secondary gastrointestinal amyloidosis associated with rheumatoid arthritis. Subsequently, her condition was not improved even after changing to total parenteral nutrition; however, after introduction of an anti-IL-6 receptor antibody, marked improvement was achieved both in clinical symptoms and endoscopic findings. Gastrointestinal amyloidosis should be considered as a differential diagnosis when a patient with chronic inflammatory disease presents with diarrhea and vomiting, and if the patient does not respond to conventional therapies, anti-IL-6 receptor antibody should be introduced at an early stage.
