Case Presentation: A four-month old full term male was admitted to the pediatric hospital medicine inpatient service with poor feeding, vomiting, and inadequate weight gain. Weight faltering was first noted at 2 months of age. At that time the pediatrician prescribed famotidine for reflux and referred the mother-infant dyad to a lactation consultant for breastfeeding support. At 4 months of age, the infant’s weight had dropped further and was less than the 0.01 percentile (Figure 1, red arrow). Nutrition supplementation via a bottle was unsuccessful due to severe gagging. Given his inability to gain weight as an outpatient, he was ultimately admitted to the hospital. Admission exam was notable for a euvolemic, well-appearing infant with a poor suck and exaggerated gag reflex. Initial laboratory results showed severe hyponatremia (serum sodium 121 mmol/L) and mild hyperkalemia (serum potassium 6.2 mmol/L). Initial serum osmolality and urine studies were difficult to interpret as the patient was started on intravenous (IV) fluids prior to collection. The hyponatremia was corrected with IV normal saline and sodium acetate before transitioning to oral sodium supplementation. The patient continued to require sodium supplementation, so aldosterone and renin labs were collected. Results revealed significant elevation to 347 ng/dL (normal range, 6.5-86 ng/dL) and 280 ng/mL/hr, (normal range, 1.4-7.8 ng/mL/hr) respectively, consistent with pseudohypoaldosteronism. With sodium supplementation to maintain normal sodium levels and a nasogastric tube to supplement his oral feeds, he was able to gain weight and discharge home. Genetic workup confirmed he had autosomal dominant pseudohypoaldosteronism type 1. At follow-up around 6 months of age, the patient was no longer requiring an NG tube and was growing well with continued sodium supplementation.
Discussion: This case illustrates a rare underlying etiology of a commonly encountered clinical presentation that is seen by pediatric hospitalists on the inpatient unit. In an infant with severe hyponatremia and euvolemic exam, there should be high suspicion for an organic etiology of weight faltering. Pseudohypoaldosteronism type 1 is a rare disorder caused by resistance to the effects of aldosterone, leading to decreased reabsorption of sodium and decreased potassium excretion by the kidneys1. The autosomal dominant form is less severe and typically presents in infancy with inadequate weight gain and labs notable for hyponatremia, hyperkalemia, and metabolic acidosis2. Patients generally do not require sodium supplementation past the age of 2 years, but it is critical for support of proper growth in infancy2. Additionally, this case serves as a reminder that if a chronic electrolyte imbalance is suspected, serum osmolality and urine studies should be obtained prior to electrolyte correction, as the inability to interpret these lab results may contribute to delayed diagnosis.
Conclusions: Weight faltering in infancy is most commonly due to inadequate caloric intake3. However, when electrolyte abnormalities are identified, other underlying causes must be considered. Pseudohypoaldosteronism type 1 is a rare disease that presents in infancy with poor growth and salt wasting, requiring sodium supplementation to support proper nutrition.
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