## Complications of Multiple Myeloma **Key Point:** Multiple myeloma is associated with multiple serious complications, but acute leukemoid reaction is NOT a typical feature. A leukemoid reaction (marked WBC elevation in response to infection, inflammation, or malignancy) can occur in myeloma patients, but it is a secondary response to infection or stress, not a direct effect of myeloma cell proliferation. ### Typical Complications of Multiple Myeloma | Complication | Mechanism | Frequency | | --- | --- | --- | | Light-chain nephropathy | Direct tubular toxicity of free light chains; cast formation in distal tubules | Very common (50%) | | Hyperviscosity syndrome | High concentration of monoclonal immunoglobulin (especially IgM, IgA) | 5–10% (more common in Waldenström) | | Tumor lysis syndrome | Rapid cell death releases intracellular contents (K⁺, phosphate, uric acid) | Uncommon spontaneously; common post-chemo | | Infections | Suppressed normal immunoglobulin production; impaired cell-mediated immunity | Very common | | Hypercalcemia | Osteoclastic bone resorption; impaired renal excretion | 20–30% | | Leukemoid reaction | Secondary to infection or inflammatory response, NOT direct myeloma effect | Uncommon and secondary | **High-Yield:** Tumor lysis syndrome CAN occur spontaneously in myeloma (especially with high tumor burden) and is a medical emergency. However, acute leukemoid reaction (WBC >50,000/μL) is NOT a direct manifestation of myeloma itself — it occurs only as a secondary response to infection or chemotherapy toxicity. **Clinical Pearl:** In a myeloma patient with WBC >50,000/μL, always search for an underlying infection (pneumonia, urinary tract infection) or other trigger. A true leukemoid reaction is not a primary complication of myeloma. **Warning:** Do not confuse leukemoid reaction (benign, reactive WBC elevation) with leukemic transformation (rare but serious complication of myeloma). Leukemic transformation is a true complication; leukemoid reaction is not. ### Why Option 3 is Correct Acute leukemoid reaction with WBC >50,000/μL is NOT a direct complication of myeloma cell proliferation. While myeloma patients can develop leukemoid reactions in response to infection or stress, this is a secondary phenomenon, not a primary manifestation of the disease. The other three options (light-chain nephropathy, hyperviscosity syndrome, and tumor lysis syndrome) are well-established, direct complications of myeloma.
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