• Satoru Kobayashi, Nana Mizuno, Kyoko Yokoi, Takayasu Mori, Eisei Sohara, and Shinichi Uchida.
• Department of Pediatrics, Nagoya City University West Medical Center, Nagoya, Japan.
• Medicine (Baltimore). 2022 Jan 21; 101 (3): e28552e28552.

RationaleAlmost 90% of congenital nephrogenic diabetes insipidus (NDI) cases are caused by mutations in the arginine vasopressin receptor 2 gene, which has X-linked recessive inheritance. Although NDI is commonly diagnosed in early infancy based on its characteristic findings, clinical diagnosis can be delayed when no other family members have been diagnosed with NDI because several findings of NDI are nonspecific.Patient ConcernsA 3-month-old boy diagnosed with NDI presenting with osmotic demyelination syndrome (ODS) was admitted for poor weight gain after birth and poor feeding during the week prior to admission.DiagnosisOn admission, the initial blood examination showed hypernatremia (158 mmol/L), and treatment with intravenous fluids over the next 2 days further elevated the serum sodium level (171 mmol/L). After admission, polyuria was recognized, and polyuria in his grandmother and mother since childhood without a diagnosis of NDI was found. Magnetic resonance imaging showed multifocal, symmetrical lesions, including the lateral pons, on diffusion- and T2-weighted imaging, which led to a diagnosis of ODS.InterventionThe infusion was stopped, and the patient was fed milk diluted 2-fold with water.OutcomesThe serum sodium level gradually decreased to 148 mmol/L over the course of 1 week. Low-sodium milk was started at 4 months of age and maintained a serum sodium level of approximately 140 mmol/L, which was within the normal range. The developmental quotient was 94 at 4 years of age.LessonsODS is an encephalopathy resulting from extreme fluctuations in serum sodium concentration and plasma osmolality. ODS due to hypernatremia has been reported in several patients, although it usually occurs during rapid correction of hyponatremia. Consequences of the central nervous system are a critical complication of NDI that affects prognosis. These consequences can be avoided with treatment. Early blood examination or polyuria in the patient, mother, or another family member and hypernatremic dehydration with good urine output should lead to an early diagnosis and prevent central nervous system consequences.Copyright © 2022 the Author(s). Published by Wolters Kluwer Health, Inc.

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