Not All Polyps Are Created Equal: Multiple Myeloma in the Gut

Background: Multiple myeloma is a neoplastic proliferation of plasma cells producing a monoclonal immunoglobulin usually restricted to the bone marrow. Recent literature confirms increased extramedullary involvement of skin, liver and lymph nodes but gastrointestinal multiple myelomas remain rare.

Case: We report a case of 57-year-old female with a past medical history of progressive multiple myeloma IgA lambda on elotuzumab, lenalidomide and dexamethasone therapy, who presented with generalized weakness and black stools for approximately one week. Initial laboratory work demonstrated a hemoglobin of 6.7 grams per deciliter and heme positive stools consistent with anemia secondary to presumed gastrointestinal blood losses. Esophagogastroduodenoscopy (EGD) was unremarkable. Colonoscopy revealed 6 colonic polyps scattered throughout the distal transverse, cecal and descending colon which were excised and sent for pathology. Pathology of the polyps showed plasma cell myeloma with anaplastic features. Immunohistochemistry demonstrated cells that were positive for CD-138 and negative for keratin staining, confirming plasma cell origin. Furthermore analysis was positive for lambda light chain, but negative for kappa light chain. The patient was managed with packed red cell transfusion with no further evidence of recurrent bleeding.

Conclusion: Gastrointestinal multiple myeloma are rare, but as our case demonstrates, they must be considered in the differential diagnosis of patients with gastrointestinal bleeding, particularly those with multiple myeloma. The endoscopic appearance of multiple myeloma polyps may be similar to other more common conditions, making pathological and immunohistochemical analysis of biopsies essential for making a correct diagnosis.