Asian Journal of Research in Nephrology

Background: Hyponatremia is a common electrolyte abnormality in kidney transplant recipients and may result from a variety of etiologies, including infections, drug effects, rejection, and hormonal disturbances. Hyponatremia due to polydipsia, however, is rarely reported in the post-transplant setting.

Case Presentation: We report the case of a 40-year-old woman with end-stage kidney disease secondary to presumed chronic interstitial nephritis who underwent deceased donor kidney transplantation. Her post-transplant course was complicated by antibody-mediated rejection, which was successfully treated with corticosteroids, plasma exchange, intravenous immunoglobulin, and rituximab, resulting in stable graft function. Seven months after transplantation, she was found to have asymptomatic severe hyponatremia (serum sodium 119 mEq/L). Evaluation revealed hypotonic hyponatremia with low urine osmolality (88 mOsm/kg) and low urine sodium (23 mEq/L), normal thyroid and adrenal function, and euvolemic clinical status. Detailed history revealed excessive water intake of approximately 5 liters per day over the preceding two weeks. The cause of polydipsia in the patient was the thought that intake of more water will lead to reduced creatinine as reinforced by one of her acquaintance, who was also a kidney transplant recipient. Fluid restriction led to immediate correction of serum sodium and normalization of urine osmolality, confirming a diagnosis of polydipsia-induced hyponatremia. The patient remained normonatremic on follow-up with stable graft function after behavioural counselling.

Conclusion: Polydipsia is an uncommon but important cause of hyponatremia in kidney transplant recipients. Careful history taking and appropriate biochemical evaluation are critical for diagnosis. Early recognition and fluid restriction with counselling can effectively prevent recurrence and serious complications.