Plasma Cell Disorders¶
Chapter 116 | Part 4: Oncology and Hematology
KEY CLINICAL POINTS¶
- Multiple myeloma (MM) is a malignant proliferation of plasma cells characterized by monoclonal gammopathy, bone lesions, renal failure, and systemic complications.
- Diagnosis requires ≥ 10% clonal plasma cells in bone marrow, serum/urine M component, and end-organ damage (CRAB criteria).
- Treatment includes IMiDs (lenalidomide), proteasome inhibitors (bortezomib), antibodies (daratumumab), and autologous stem cell transplantation (ASCT).
- Prognosis is influenced by ISS staging, β -microglobulin, and genetic abnormalities like del(17p) or t(4;14).
- Hyperviscosity, renal failure, and infections are major complications requiring plasmapheresis and supportive care.
1. DEFINITION & OVERVIEW¶
Plasma cell disorders encompass monoclonal gammopathies, including multiple myeloma (MM), Waldenström’s macroglobulinemia, and heavy chain diseases. These conditions arise from clonal expansion of plasma cells, leading to secretion of monoclonal immunoglobulins (M components) and systemic complications.
Table 116-1: Diagnostic Criteria for Multiple Myeloma¶
| Criteria | MGUS | Smoldering MM | Symptomatic MM |
|---|---|---|---|
| Serum monoclonal protein | <30 g/L | ‡30 g/L | ‡30 g/L |
| Bone marrow plasma cells | <10% | 10–60% | ‡10% |
| End-organ damage (CRAB) | Absent | Absent | Present |
1.1 Classification¶
Monoclonal gammopathies are classified by immunoglobulin type (IgG, IgA, IgM) and light/heavy chain involvement. Key subtypes include MM, Waldenström’s macroglobulinemia, and heavy chain diseases (gamma, alpha, mu).
1.2 Pathogenesis¶
Genetic mutations (KRAS, NRAS, TP53) and cytokine dysregulation (IL-6, VEGF) drive clonal expansion. Interaction with bone marrow stromal cells promotes tumor survival and drug resistance.
2. EPIDEMIOLOGY¶
MM incidence peaks at 69 years, with higher rates in blacks (8.1–17.1/100,000) and Pacific Islanders. Global incidence varies, with higher prevalence in developed countries due to longer life expectancy. Waldenström’s macroglobulinemia is more common in men and older adults.
2.1 Risk Factors¶
Exposure to radiation, agricultural work, and certain occupations (e.g., farmers, leather workers) increase risk. Genetic predisposition and family history are noted in Waldenström’s macroglobulinemia.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Genetic mutations (KRAS, TP53, del(17p)) and dysregulated cytokine signaling (IL-6, VEGF) drive pathogenesis. Bone marrow microenvironment interactions and immune evasion mechanisms contribute to disease progression.
Table 116-3: Risk Stratification in Myeloma¶
| Risk Category | Features | Median Survival (Months) |
|---|---|---|
| Standard Risk | bM <3.5, ALB ‡3.5 | 62 |
| High Risk | bM >5.5 or bM <3.5, ALB <3.5 | 29 |
3.1 Molecular Mechanisms¶
Mutations in BTK, MYD88, and CXCR4 disrupt normal B-cell signaling. Proteasome inhibition and cytokine overproduction (IL-6) promote tumor survival and resistance.
4. CLINICAL FEATURES¶
Key symptoms include bone pain, hypercalcemia, renal failure, anemia, and neuropathy. Hyperviscosity (common in IgM) and Bence Jones proteinuria are critical manifestations.
4.1 Complications¶
Renal failure from light chain deposition, infections due to immunosuppression, and osteolytic bone lesions are major complications. Hyperviscosity syndrome may cause visual disturbances and neurological deficits.
5. DIFFERENTIAL DIAGNOSIS¶
Differentiate from MGUS, smoldering MM, and other lymphoproliferative disorders. Amyloidosis, chronic lymphocytic leukemia, and non-neoplastic conditions (e.g., sarcoidosis) must be excluded.
5.1 Key Differentiators¶
Presence of end-organ damage (CRAB criteria), bone lesions, and monoclonal proteinuria distinguish MM from MGUS. Waldenström’s macroglobulinemia is differentiated by lymphoplasmacytic infiltration and IgM paraprotein.
6. INVESTIGATIONS & DIAGNOSIS¶
Serum/urine protein electrophoresis, immunofixation, and free light chain assays are essential. Bone marrow biopsy and imaging (PET/CT) confirm diagnosis. ISS staging and β -microglobulin levels guide prognosis.
Table 116-2: Standard Investigative Workup¶
| Test | Purpose |
|---|---|
| Bone marrow biopsy | Confirm clonal plasma cells |
| Serum protein electrophoresis | Detect M component |
| Immunofixation | Identify immunoglobulin type |
| Free light chain assay | Assess ratio and concentration |
6.1 Diagnostic Tests¶
Serum free light chain ratio (>100), bone marrow plasma cells (>10%), and M component quantitation ( ≥ 30 g/L) are critical. Renal function tests and calcium levels assess complications.
7. MANAGEMENT & TREATMENT¶
Induction therapy combines IMiDs, proteasome inhibitors, and antibodies. ASCT is used in eligible patients. Maintenance and relapsed/refractory disease require novel agents like daratumumab and CAR-T.
Table 116-4: Standard Therapeutic Agents¶
| Class | Agent | Indication |
|---|---|---|
| IMiD | Lenalidomide | Newly diagnosed and relapsed |
| Proteasome Inhibitor | Bortezomib | Newly diagnosed and relapsed |
| Antibody | Daratumumab | Relapsed/refractory |
7.1 Treatment Algorithm¶
First-line: DRd (dara + lenalidomide + dexamethasone) or RVD (lenalidomide + bortezomib + dexamethasone). Relapsed disease: carfilzomib, ixazomib, or bispecific antibodies (e.g., teclistamab).
8. PROGNOSIS & COMPLICATIONS¶
Median survival is 8–10 years with modern therapies. Prognostic factors include ISS stage, β -microglobulin, and genetic abnormalities. Complications include renal failure, infections, and treatment-related myelodysplasia.
8.1 Survival Outcomes¶
ISS stage I: ~62 months; stage III: ~29 months. High-risk features (del(17p), t(4;14)) correlate with shorter survival.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: Monitor for hypercalcemia and fetal complications. Elderly patients require dose adjustments. Waldenström’s macroglobulinemia is managed with BTK inhibitors (ibrutinib) and rituximab.
9.1 Pediatric Considerations¶
Solitary plasmacytoma in children may respond to radiation. Avoid nephrotoxic agents in renal impairment.
10. KEY POINTS & CLINICAL PEARLS¶
- Early detection of CRAB criteria (hypercalcemia, renal failure, anemia, bone lesions) is critical for management.
- Plasmapheresis is essential for hyperviscosity and acute renal failure.
- Novel agents (e.g., daratumumab, carfilzomib) improve outcomes in relapsed/refractory disease.
- Monitor for treatment-related toxicities (e.g., infections, myelodysplasia).