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Medullary Sponge Kidney Distal RTA Association — ESENeph MCQ

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ModerateTubular DisordersMedullary Sponge Kidney Distal RTA AssociationESENeph

A 40-year-old woman with known medullary sponge kidney presents with recurrent calcium phosphate stones and UTIs. Her urine pH is persistently >6.5. She has a non-anion gap metabolic acidosis with hypokalaemia. What underlying tubular defect explains both the stones and the acidosis?

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Correct answer: B — Distal (type 1) renal tubular acidosis with incomplete acidification

Medullary sponge kidney (MSK) is frequently associated with distal (type 1) RTA due to structural abnormalities in the collecting ducts. The inability to acidify urine below pH 5.5 leads to alkaline urine, which promotes calcium phosphate (apatite) stone formation. The incomplete urinary acidification also causes systemic non-anion gap metabolic acidosis with compensatory renal potassium wasting (hypokalaemia). Recurrent UTIs occur because of urinary stasis within the dilated medullary collecting ducts. Treatment includes potassium citrate (corrects acidosis, provides citrate inhibitor, and replaces potassium) and prophylactic antibiotics if UTIs are recurrent.

Reference: Gambaro et al 2013 – Medullary Sponge Kidney; JRCPTB 2022 – Nephrology Curriculum