Introduction:
Multiple myeloma (MM) is a B cell neoplasm characterized by the clonal proliferation of neoplastic plasma cells in the bone marrow. [1] [2] It accounts for roughly 2 percent of all cancers and about 17 % of all hematological malignancies with an incidence rate of 7.1 % cases per 100,000 per year. Extramedullary involvement outside the bone marrow is frequently seen in advanced or refractory stages of multiple myeloma due to plasma cell infiltration of visceral organs. [3] [4] Malignant myelomatous pleural effusion or ascites is suggestive of a more advanced and aggressive disease and is seen in less than 1 % of myeloma cases. [5] [6] Ascites in MM can develop due to peritoneal infiltration or secondary causes such as hepatic amyloidosis, cardiac or renal diseases, or portal hypertension. [7] Infectious peritonitis due to tuberculosis and spontaneous bacterial peritonitis (SBP) can also be an intrinsic secondary cause of ascites but is usually differentiated from malignant plasmacytic ascites based on an ascitic fluid cytology analysis. [8] [9] Since the atypical plasma cells detected on cytology of the fluid might appear similar to reactive mesothelial cells, further testing methods such as flow cytometry, immunofluorescence, or electron microscopy should be employed. [8] Herein, we describe a case of malignant plasmacytic ascites and pleural effusion that was initially treated as SBP.