Background: Hyponatremia is a common diagnostic challenge. Methods: An index case is presented to discuss the diagnostic approach to chronic and unexplained hyponatremia. Results: The index case concerns a 60-year-old man with chronic hepatitis C and previous alcohol use who was referred because of weight loss, poor dietary intake, dizzy spells, and unexplained hyponatremia (serum sodium 124-129 mmol/l). A low urine sodium concentration (20 mmol/l) and a lowfractional sodium excretion (0.07%) were observed repeatedly, while urine osmolality washigh (>400 mosm/kg). The central questions in this case are: what is the differential diagnosis, which tests are needed to confirm or exclude a diagnosis, and how would you proceed if no obvious cause is found? Conclusions: The diagnosis of this case of unexplained hyponatremia was unexpected, but important because it was treatable. The challenges and caveats of the diagnostic approach to hyponatremia are discussed. A diagnostic algorithm to guide clinicians who are confronted with similar cases is presented. Copyright

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Nephron Physiology
Erasmus MC: University Medical Center Rotterdam

Hoorn, E.J, Hotho, D.M, Hassing, R.J, & Zietse, R. (2011). Unexplained hyponatremia: Seek and you will find. Nephron Physiology, 118(3). doi:10.1159/000322240