Exercise-Associated Hyponatraemia — ESENeph MCQ

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ModerateElectrolyte DisordersExercise-Associated HyponatraemiaESENeph

A 42-year-old woman presents with serum sodium 115 mmol/L and seizures. She is a marathon runner who drank excessive water during a race. Urine osmolality is 45 mOsm/kg. What is the diagnosis?

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Correct answer: E — Exercise-associated hyponatraemia (water intoxication/primary polydipsia)

Dilute urine (osmolality <100 mOsm/kg) with severe hyponatraemia in the context of excessive water intake during exercise is diagnostic of exercise-associated hyponatraemia (EAH) from water intoxication. The kidneys are appropriately diluting urine but cannot excrete water fast enough to match the massive intake. In SIADH, urine would be inappropriately concentrated (>100 mOsm/kg). Treatment of seizures requires 3% hypertonic saline bolus. Fluid restriction is the ongoing management.

Reference: Spasovski et al 2014 – Hyponatraemia Guideline; Hew-Butler et al 2015 – EAH Consensus