A 6-year-old boy receiving induction chemotherapy for Burkitt lymphoma develops cardiac arrhythmia within 48 hours. Labs show potassium 7.1 mmol/L, phosphate 8.5 mg/dL, uric acid 22 mg/dL, calcium 6.0 mg/dL, and creatinine 3.2 mg/dL. The hypocalcaemia in this syndrome results directly from:
- A Chemotherapy-induced destruction of parathyroid glands
- B Uric acid crystals binding ionised calcium in the renal tubules
- C Precipitation of calcium phosphate in soft tissues driven by the marked hyperphosphataemia ✓
- D Lactate released from lysed lymphoblasts chelating serum calcium
Correct answer: C. Precipitation of calcium phosphate in soft tissues driven by the marked hyperphosphataemia
Explanation
This is tumour lysis syndrome from massive tumour cell breakdown, releasing potassium, phosphate, nucleic acids and lactate dehydrogenase. Purine catabolism produces hyperuricaemia, and the extreme hyperphosphataemia complexes with calcium, depositing calcium phosphate in tissues and causing symptomatic hypocalcaemia. Uric acid contributes to acute kidney injury but does not bind calcium, killing option B.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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