Introduction: Hypernatremia in preterm babies is often due to insensible water loss, inadequate fluid intake or sodium imbalance due to immature kidneys. Congenital nephrogenic diabetes insipidus (CNDI) is an uncommon cause of hypernatremia in neonates and presents shortly after birth. Early recognition is important to prevent severe dehydration, electrolytes imbalance and neurological complications. Case: We report a case of a preterm 32-week female infant, with a birth weight of 1.14 kg with persistent hypernatremia (146– 156 mmol/L) from day 4 of life. She received total parenteral nutrition since birth and was started on breastmilk since day 5 of life. The baby was mildly dehydrated with weight loss and high urea (6.5 mmol/L) at day 7 of life. Total fluids were increased to 160 mL/kg/day but serum sodium remained elevated even though the urea had normalized. The infant was also noted to have high urine output (5–6 mL/kg/hour) since day 3 of life and suboptimal weight gain. Further evaluation at age 1 month revealed urine osmolality 71 mOsm/kg, serum osmolality 308 mOsm/kg and urine sodium <20 mmol/L when serum sodium was 150 mmol/L, suggestive of DI. A trial of desmopressin showed unchanged serum sodium (Na), suggesting nephrogenic DI. Administration of intravenous fluids of 1/5NSD10% resulted in further increase of both sodium (159 mmol/L) and serum osmolality (326 mOsm/kg) with low urine osmolality (111 mOsm/kg). Intravenous fluids were discontinued and she was started on hydrochlorothiazide (1 mg/kg/dose bd), resulting in gradual normalization of sodium 138 mmol/L. Post discharge, she had good weight gain and normal developmental milestones at corrected age of 1.5-month-old. Due to early onset hypernatremia, the infant was referred for genetic testing to rule out CNDI. Conclusion Early onset persistent hypernatremia and high urine output despite adequate fluid management should prompt evaluation of DI. Early diagnosis is crucial to prevent a chronic state of hypernatremia that can lead to growth and developmental delay.
Infant, Newborn ; Dehydration ; Hypernatremia