Case report：Multiple myeloma with gastrointestinal amyloidosisHuimin Qi1+,Qiwen Wang1,Xuxin Zhang1,Hui Qi2,Xiaoling Ding1*1Department of Gastroenterology, Affiliated Hospital of Nantong University, Nantong, 226001, China2School of Medicine, Xinglin College, Nantong University，Nantong, 226001, ChinaCorrespondence:Xiaoling DingDixili@126.com+These authors contributed equally to this workIntroduction: Multiple myeloma ( MM ) combined with gastrointestinal amyloidosis is rare in clinic, and early diagnosis is difficult. This case suggests that for elderly patients with multi-system involvement, especially with unexplained gastrointestinal symptoms, the possibility of MM combined with amyloidosis should be alerted. If necessary, deep tissue biopsy or surgical specimen pathological examination should be performed to confirm the diagnosis.Case Report: This paper reports a 74-year-old male patient who was diagnosed as inflammatory bowel disease due to repeated abdominal pain and hematochezia. Congo red staining was negative in multiple endoscopic biopsies at the initial stage. After serum free light chain detection, echocardiography, renal biopsy and bone marrow biopsy, the patient was diagnosed as MM with renal and cardiac amyloidosis. Then, the colon specimens were surgically removed for pathological examination, and Congo red staining positive amyloid deposition was found in the submucosa. Finally, the patient was diagnosed as multiple myeloma with gastrointestinal amyloidosis.Conclusion: Multiple myeloma with gastrointestinal amyloidosis often overlaps with other gastrointestinal diseases in clinical manifestations, so it is prone to misdiagnosis or missed diagnosis during diagnosis and treatment. Early diagnosis and appropriate treatment are essential for delaying disease progression, improving patients ’ quality of life and prolonging survival. If necessary, they should be referred to the corresponding specialist for systematic diagnosis and treatment in time.