Malnutrition and hypernatremic dehydration as the initial presentation of nephrogenic diabetes insipidus in an infant.

Congenital nephrogenic diabetes insipidus (CNDI), also known as arginine vasopressin resistance, is a rare inherited disorder of water homeostasis in which the kidneys lose their ability to concentrate urine, leading to polyuria, polydipsia, and a risk of hypertonic dehydration. We report the case of a 3-month-old infant with symptoms present for approximately 2 months, characterized by episodes of fever, irritability, and poor growth. Upon admission, severe malnutrition and dehydration were noted. A diagnosis of CNDI was made based on vasopressin levels, plasma and urine osmolarity values, hypernatremia, and family history. The patient's treatment was challenging; he responded favorably and remains under outpatient follow-up. The presentation, results of additional tests, and short-term course are described.