Plasma Cell Disorders

Plasma Cell Disorders & MGUS - Gammopathy Genesis

• Arise from clonal plasma cell proliferation, leading to monoclonal gammopathies.
• Key feature: Secretion of monoclonal immunoglobulin (M-protein).
  • Identified by Serum Protein Electrophoresis (SPEP) showing an M-spike.
• MGUS (Monoclonal Gammopathy of Undetermined Significance):
  • Earliest detectable, asymptomatic precursor lesion.
  • Criteria:
    • Serum M-protein < 3 g/dL.
    • Bone marrow clonal plasma cells < 10%.
    • No end-organ damage (CRAB: Hypercalcemia, Renal failure, Anemia, Bone lesions) or related symptoms.

  ⭐ MGUS progresses to MM or other lymphoproliferative disorders at a rate of approximately 1% per year.

Multiple Myeloma - CRAB's Cruel Reign

Malignant proliferation of plasma cells in bone marrow (BM), producing monoclonal immunoglobulin (M-protein).

• Key Diagnostic Markers:
  • Clonal BM plasma cells >10% or biopsy-proven plasmacytoma.
  • M-protein in serum and/or urine (IgG most common, then IgA).
  • Often: Bence Jones proteinuria (free light chains).
• 📌 CRAB Criteria (Myeloma-Defining End-Organ Damage):
  • Calcium elevation: Serum Ca >11 mg/dL (or >0.25 mmol/L above ULN).
  • Renal insufficiency: Serum Creatinine >2 mg/dL (or CrCl <40 mL/min).
  • Anemia: Hb <10 g/dL (or >2 g/dL below normal).
  • Bone lesions: ≥1 lytic lesion on imaging (X-ray, CT, PET-CT).

⭐ Lytic bone lesions in Multiple Myeloma are characteristically 'cold' on technetium-99m bone scans because osteoblastic activity is suppressed.

Myeloma's Kin & WM - Variant Vignettes

• Smoldering Multiple Myeloma (SMM)
  • Asymptomatic; M-protein (IgG/IgA) ≥3 g/dL or urine ≥500 mg/24h.
  • BMPCs 10-60%.
  • NO CRAB.
  • Risk to MM: ~10%/yr (first 5 yrs).
• Plasma Cell Leukemia (PCL)
  • Aggressive; PB plasma cells >20% or absolute >2x10⁹/L.
  • Primary (de novo) or secondary (from MM). Poor prognosis.
• Waldenström Macroglobulinemia (WM)
  • LPL with IgM gammopathy.
  • BM: ≥10% LPL infiltration.
  • MYD88 L265P (>90%).
  • Clinical: Hyperviscosity (visual, neuro, bleeding), anemia, organomegaly. No lytic lesions.

⭐ Waldenström Macroglobulinemia is defined by IgM monoclonal gammopathy and ≥10% lymphoplasmacytic infiltration in bone marrow, often causing hyperviscosity.

Diagnosis & Amyloidosis - Detect & Disrupt

• Screening Tests:
  • Serum Protein Electrophoresis (SPEP): M-spike detection.
  • Serum Free Light Chain (FLC) Assay: Abnormal κ/λ ratio.
• Definitive Diagnosis:
  • Immunofixation: M-protein typing.
  • Bone Marrow Biopsy: Plasma cell percentage (e.g., >10% in Myeloma).
• AL Amyloidosis:
  • Light chain deposition disease; systemic.
  • Diagnosis: Tissue biopsy + Congo Red stain.

  ⭐ AL Amyloidosis demonstrates apple-green birefringence with Congo red stain under polarized light, pathognomonic for amyloid fibrils.

High‑Yield Points - ⚡ Biggest Takeaways

• Multiple Myeloma: Defined by CRAB criteria (Hypercalcemia, Renal failure, Anemia, Bone lesions), M-spike, and Bence Jones proteinuria.
• Waldenström Macroglobulinemia: IgM hypersecretion causing hyperviscosity syndrome; no lytic bone lesions.
• MGUS: Asymptomatic M-protein without end-organ damage; risk of progression to myeloma.
• AL Amyloidosis: Monoclonal light chain deposition; Congo Red stain shows apple-green birefringence.
• Rouleaux formation on peripheral smear is common in Multiple Myeloma.