Multiple Myeloma

Definition

Multiple myeloma (MM) is a malignant plasma cell disorder characterized by clonal proliferation of plasma cells in the bone marrow, leading to bone destruction, anemia, renal impairment, and immunodeficiency.

Epidemiology

• Accounts for ~1% of all cancers and ~10% of hematologic malignancies
• Median age at diagnosis: 65–70 years
• Slight male predominance
• More common in African-American populations
• Incidence increases with age; rare under 40 years

Etiology

• Exact cause unknown; likely multifactorial
• Genetic abnormalities: translocations involving IgH locus, del(17p), t(4;14), t(14;16)
• Environmental exposures: radiation, pesticides, industrial chemicals
• Family history of plasma cell disorders
• Chronic immune stimulation and obesity may contribute

Pathophysiology

• Clonal plasma cell proliferation in bone marrow
• Production of monoclonal immunoglobulin (M protein) or light chains
• Osteoclast activation and bone resorption leading to lytic lesions
• Suppression of normal hematopoiesis causing anemia, leukopenia, thrombocytopenia
• Renal damage due to light chain deposition (cast nephropathy)
• Immunodeficiency from impaired normal antibody production