An Unusual Presentation of Hyponatremia in a Premature Infant With Failure to Thrive

Hyponatremia in neonates is a rare but not uncommon finding, especially among preterm neonates, and can be life-threatening, requiring careful diagnostic evaluation and management. We describe a two-month-old infant born at 33 weeks of gestation presenting with severe hyponatremia and failure to thrive (FTT) to highlight the diagnostic and management approach and challenges in such cases. A two-month-old male child presented with abdominal distension and poor weight gain. Admission weight was 2.72 kgs (<3rd percentile). Lab results revealed a serum sodium of 108 mEq/L and potassium of 2.6 mEq/L. X-ray abdomen and ultrasounds were unremarkable for biliary or gastrointestinal obstruction. Electrolyte abnormalities were successfully corrected with potassium chloride and normal saline. This case demonstrates the importance of assessing feeding adequacy, renal salt wasting, and potential endocrine/metabolic causes in infants with FTT and electrolyte disturbances. Timely recognition and targeted therapy for neonatal and infantile hyponatremia are crucial to prevent complications.