A Case of Multiple Myeloma Associated with Extramedullary Plasmacytoma of the Gallbladder Manifesting as Acute Cholecystitis.

Multiple myeloma (MM) is a common hematological malignancy that represents 1% of all cancers. MM is distinguished from other plasma cell disorders by prominent bone marrow involvement and systemic organ damage. Extramedullary plasmacytomas of the gall bladder (GB) or biliary ducts, whether solitary or in association with MM, are very rare. We report a case of a 66-year-old female with a history of refractory MM who presented with right upper quadrant abdominal pain. Her laboratory evaluation revealed an abnormal liver panel and lactic acidosis. Abdominal ultrasonography was consistent with acute cholecystitis with no evidence of biliary obstruction or abnormal liver parenchyma. An open cholecystectomy with liver biopsy was performed. The histological evaluation revealed involvement of the GB submucosa and serosa, as well as the liver parenchyma by abnormal plasma cells with lambda light chain restriction. Congo red stain for the GB sample was positive. The patient declined further treatment for MM and was discharged home with comfort measures.