Topiramate Nephrolithiasis — RACP Adult Medicine MCQ

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HardNephrologyTopiramate NephrolithiasisRACP Adult Medicine

A 50-year-old woman with chronic migraine on topiramate develops renal colic. CT KUB shows a 5 mm radiolucent stone in the right distal ureter. What type of stone is most associated with topiramate?

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Correct answer: A — Cystine

Topiramate inhibits carbonic anhydrase in the renal tubule, causing metabolic acidosis, alkaline urine, and reduced urinary citrate excretion. This predisposes to calcium phosphate stone formation (not calcium oxalate or uric acid). The risk is dose-dependent. Patients on topiramate should maintain adequate hydration. Calcium phosphate stones are radiopaque, but the question states radiolucent – in practice topiramate stones can be mixed composition. Nonetheless, calcium phosphate is the characteristic association.

Reference: AMH – 2025 – Topiramate; eTG – 2025 – Nephrology