A 62-year-old man from Delhi presents with persistent lower back pain for 3 months and progressive fatigue. On examination, he appears pale. Laboratory investigations reveal: hemoglobin 8.2 g/dL, serum calcium 11.8 mg/dL, serum creatinine 2.1 mg/dL, and serum albumin 2.8 g/dL. Serum protein electrophoresis shows an M-spike of 4.2 g/dL in the gamma region. Bone marrow biopsy reveals 35% plasma cells with abnormal morphology. Which of the following is the most likely diagnosis?

Question

Accepted Answer

C. Multiple myeloma. ## Diagnostic Approach to Plasma Cell Dyscrasias **Key Point:** Multiple myeloma is diagnosed when ≥10% clonal bone marrow plasma cells OR ≥30% clonal bone marrow plasma cells (regardless of CRAB criteria) are present, along with myeloma-defining events. ### Clinical Features Present in This Case | Feature | Finding | Significance | |---------|---------|---------------| | Bone marrow plasma cells | 35% | Meets diagnostic threshold (≥10%) | | M-spike | 4.2 g/dL | Significant monoclonal protein | | Hypercalcemia | 11.8 mg/dL | CRAB criterion (C = Calcium) | | Renal impairment | Cr 2.1 mg/dL | CRAB criterion (R = Renal) | | Anemia | Hb 8.2 g/dL | CRAB criterion (A = Anemia) | | Bone pain | Lower back pain | CRAB criterion (B = Bone lesions) | | Hypoalbuminemia | 2.8 g/dL | Reflects disease burden | **High-Yield:** The patient meets BOTH diagnostic criteria: 1. ≥10% clonal bone marrow plasma cells (35% present) 2. ≥1 CRAB criterion (has all four: hypercalcemia, renal failure, anemia, bone disease) ### Why This Is Multiple Myeloma and Not MGUS **Clinical Pearl:** MGUS has <10% bone marrow plasma cells, <3 g/dL M-spike, and NO end-organ damage. This patient has 35% plasma cells + CRAB criteria, making myeloma certain. ### Diagnostic Algorithm ```mermaid flowchart TD A[Monoclonal protein detected]:::outcome --> B{Bone marrow plasma cells?}:::decision B -->|<10%| C{CRAB criteria present?}:::decision B -->|≥10%| D[Myeloma-defining event present?]:::decision C -->|No| E[MGUS]:::outcome C -->|Yes| F[Smoldering myeloma]:::outcome D -->|Yes| G[Multiple Myeloma]:::action D -->|No| H[Asymptomatic myeloma]:::outcome A --> I{IgM type?}:::decision I -->|Yes + lymphadenopathy| J[Waldenström macroglobulinemia]:::outcome I -->|No| B ``` **Mnemonic: CRAB criteria** — **C**alcium elevation, **R**enal insufficiency, **A**nemia, **B**one lesions **Key Point:** Modern diagnostic criteria (IMWG 2014) also include myeloma-defining events: - ≥60% clonal bone marrow plasma cells - Involved/uninvolved free light chain ratio ≥100 - >1 focal lesion on MRI This patient clearly has multiple myeloma based on both classical CRAB criteria and elevated plasma cell percentage.

Answer

A. Waldenström macroglobulinemia

Answer

B. Light chain disease

Answer

D. Monoclonal gammopathy of undetermined significance (MGUS)

Explanation

Diagnostic Approach to Plasma Cell Dyscrasias

Clinical Features Present in This Case

Why This Is Multiple Myeloma and Not MGUS

Diagnostic Algorithm

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Feature	Finding	Significance
Bone marrow plasma cells	35%	Meets diagnostic threshold (≥10%)
M-spike	4.2 g/dL	Significant monoclonal protein
Hypercalcemia	11.8 mg/dL	CRAB criterion (C = Calcium)
Renal impairment	Cr 2.1 mg/dL	CRAB criterion (R = Renal)
Anemia	Hb 8.2 g/dL	CRAB criterion (A = Anemia)
Bone pain	Lower back pain	CRAB criterion (B = Bone lesions)
Hypoalbuminemia	2.8 g/dL	Reflects disease burden