Hypernatremia secondary to partial urinary tract obstruction: a case report.

Introduction: This case report describes a 52-year-old male with a 6-month history of polydipsia and polyuria, and increased urinary foam for 2 months. He was initially diagnosed with type 2 diabetes mellitus complicated by hyperglycemic hyperosmolar state (HHS). Despite stabilization of blood glucose, he developed refractory, unexplained severe hypernatremia. Methods: The patient received standard care including insulin therapy and fluid resuscitation. Due to the persistent hypernatremia and the known concurrent conditions of benign prostatic hyperplasia, bilateral hydronephrosis with ureteral dilation, and bladder calculi, he subsequently underwent transurethral holmium laser enucleation of the prostate and cystolithotripsy. Results: Following the urological surgery, the patient's serum sodium level rapidly normalized, decreasing from a peak of 162.3 mmol/L to 139.7 mmol/L, with complete resolution of the hypernatremia. Discussion: This case illustrates that partial urinary tract obstruction can induce hypernatremia by impairing renal medullary concentrating ability and sodium-water reabsorption, leading to a disproportionate loss of water relative to sodium. It highlights the critical importance of actively investigating urinary tract obstruction in patients with unexplained hypernatremia, particularly those with urological symptoms or elderly males. Early surgical intervention to relieve the obstruction can significantly improve the prognosis.