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

Chronic hyponatremia, Hyponatremia, Syndrome of inappropriate antidiuresis, Syndrome of inappropriate antidiuretic hormone secretion, Unexplained hyponatremia,
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