Multiple Myeloma

Introduction

Multiple myeloma is cancer of monoclonal plasma cells
- produces large amounts of IgG (55%) or IgA (25%)
- high levels of IL-6 may be present
Epidemiology
- most common primary tumor arising within bone in the elderly
If asymptomatic
- called monoclonal gammopathy of undetermined significance (MGUS)
- increased gamma globulin on serum electrophoresis but no symptoms of multiple myeloma are present
Pathophysiology
- initial event – abnormal response of B lymphocyte to antigenic stimulation results in monoclonal proliferation of plasma cells -> MGUS
- additional mutations causes progression from MGUS to multiple myeloma
- since the plasma cell population in multiple myeloma are clones, they produce the same antibody, resulting in the monoclonal M spike on serum protein electrophoresis
though total serum antibody levels increase, these antibodies do not provide protection against pathogens because there is a lack of antibody antigenic diversity

Presentation

Evaluation

Serum protein electrophoresis
- monoclonal immunoglobulin spike (M protein)
Urinalysis
- Ig light chains (Bence Jones protein)
Peripheral blood smear
- Russell bodies
  - Ig containing inclusion bodies seen in plasma cells
- RBC rouleaux formation
  - Igs coat RBC and neutralize the ionic charge than normally repels RBCs
Bone marrow aspiration
- proliferation of large monoclonal plasma cells
  - “fried-egg” appearance
Serology
- hypercalcemia
  - result of bone degradation due to cytokine production that activates RANK receptor on osteoclasts
  - associated with decreased phosphate, increased PTH-rp and decreased vitamin D levels
- prolonged bleeding time
Imaging
punched-out lytic bone lesions on x-ray

Prognosis, Prevention, and Complications

May lead to
- renal insufficiency
- ↑ susceptibility to infection
- anemia
- primary amyloidosis (AL)
Poor prognosis