A 55-year-old man complains of pain in his back, fatigue and occasional confusion. He admits to polyuria and polydipsia. An X-ray examination reveals numerous lytic lesions in the lumbar vertebral bodies. Laboratory studies disclose hypoalbuminemia, mild anemia, and thrombocytopenia. A monoclonal Igk peak is demonstrated by serum electrophoresis. Urinalysis shows 4+ proteinuria. A bone marrow biopsy discloses foci of plasma cells, which account for 18% of all hematopoietic cells. What is the appropriate diagnosis?

Plasma cell myeloma (multiple myeloma) is characterized by a multifocal infiltration of malignant plasma cells in the bone marrow. There are typically multiple destructive lytic lesions or diffuse demineralization of bone. Major diagnostic criteria for plasma cell myeloma include marrow plasmacytosis (>30%), plasmacytoma on biopsy, and immunoglobulin paraprotein (M-component). Neoplastic cells typically secrete a homogeneous complete or partial immunoglobulin chain, which can be seen in serum or urine electrophoresis. In this patient, the neoplastic clone secretes excess kappa light chains. Waldenstrom macroglobulinemia (choice E) is a neoplastic disorder of small lymphocytes that secrete IgM.Diagnosis: Multiple myeloma