Which cell type predominates in the bone marrow of a patient with multiple myeloma?

Correct answer: B. Plasma cells

• A. Eosinophilia points toward parasitic infection, allergic disease or eosinophilic granuloma, not myeloma.
• B. CORRECT. Multiple myeloma is a malignant clonal proliferation of PLASMA CELLS — terminally differentiated B lymphocytes — within the bone marrow. The diagnostic threshold is generally 10% or more clonal plasma cells on marrow examination, and these cells secrete a monoclonal immunoglobulin detectable as an M spike on serum protein electrophoresis.
• C. Neutrophil predominance suggests acute bacterial infection or a myeloproliferative disorder.
• D. Lymphocyte predominance in the marrow suggests chronic lymphocytic leukaemia or lymphoma.

Note: The dental relevance is real: multiple myeloma produces multiple well-defined 'punched-out' radiolucencies of the skull and jaws with no surrounding sclerosis, and the mandible is involved in a substantial proportion of cases. The dentist may make the first observation. Remember CRAB for the diagnostic features — hyperCalcemia, Renal impairment, Anaemia, Bone lesions — and note that these patients are frequently on bisphosphonates or denosumab, which brings MRONJ risk into every treatment decision.