Severe Hypernatremia From a Urea-Induced Diuresis due to Body Protein Wasting in an Insulin-Resistant Type 2 Diabetic Patient

Context: Hypernatremia is encountered after pituitary or hypothalamic surgery and typically is secondary to vasopressin deficiency resulting in increased free water clearance with inadequate water replacement. Objective: We report a type 2 diabetic patient with severe hypernatremia (Na+ = 161 mEq/L) after hypothalamic surgery. Unexpectedly, this was accompanied by persistent urinary hypertonicity and negative total but positive electrolyte free water clearance. Main Outcome Measure: Measurement of urinary electrolytes and urea revealed that an osmotic diuresis induced by urea derived principally by breakdown of endogenous protein was causative. Body protein losses over 48 hours were estimated to exceed 2 kg of lean mass. High-dose glucocorticoid, insulin resistance, and a postsurgical catabolic stress likely contributed. Conclusion: In surgically severely stressed individuals, proteolysis of endogenous protein can strongly impact body water metabolism and contribute to severe hypernatremia.