Poor Feeding, Weight Loss, and Electrolyte Abnormalities in a Term Infant

Abstract

A 2-week-old male presented with poor feeding and weight loss. His birth history included an uncomplicated pregnancy followed by a normal term vaginal delivery with a birth weight of 3.23 kg, and an uncomplicated newborn stay.During his second week of life, he developed nonbloody, nonbilious emesis with nearly every feed. On the day of admission, he presented to his pediatrician for decreased oral intake, decreased urine output, and increased sleepiness requiring arousal for feedings. Given the concern for dehydration the patient was sent to the emergency room. Vital signs revealed a temperature of 99.1°F, respiratory rate of 36 breaths/min, heart rate of 187 beats/min, and oxygen saturation of 97% on room air. He weighed 3.03 kg, down 6% from his birth weight. His examination was pertinent for a flat anterior fontanelle, dry mucous membranes, 2+ brachial and femoral pulses, normal skin turgor with normal male genitalia, and absence of abnormal skin discoloration or birthmarks. Laboratory tests revealed sodium of 123 mmol/L, potassium 5.9 mmol/L, chloride 90 mmol/L, bicarbonate 20 mmol/L, blood urea nitrogen 18 mg/dL, creatinine 0.5 mg/dL, glucose 112 mg/dL, and calcium 10.6 mg/dL. His complete blood count and urinalysis were unremarkable. Abdominal and chest radiographs were normal. He received two 20 mL/kg normal saline boluses and was started on maintenance intravenous fluids of normal saline. He was transferred to our institution for evaluation of possible pyloric stenosis.At our institution, the patient's pyloric ultrasound was normal. On arrival a venous blood gas showed a pH 7.29, partial pressure of carbon dioxide of 48 mm Hg, partial pressure of oxygen of 33 mm Hg, and bicarbonate 23 mmol/L. He remained hyponatremic with serum sodium of 126 mmol/L. His serum creatinine was <0.1 mg/dL verifying normal glomerular filtration rate. He received 40 mL/kg of normal saline bringing his total sodium repletion since start of fluid resuscitation to 18 mEq/kg, with a corrected sodium of only 131 mmol/L and stable potassium level of 5.9 mmol/L. The patient was admitted for persistent hyponatremia and poor feeding.Because of persistent hyponatremia, mild hyperkalemia, and concerns for an abnormality in the adrenal axis, pediatric nephrology and endocrinology were consulted. The patient had a normal renal ultrasound with no evidence of obstruction, normal parenchymal thickness, echogenicity, and corticomedullary differentiation. A cranial ultrasound was unremarkable. Further evaluation revealed an adrenocorticotropic hormone (ACTH) level of 12 pg/mL and a cortisol level of 1.6 µg/dL (age appropriate level of 2 µg/dL). Follow-up cortisol levels were 1.7 and 1.0 µg/dL. Given persistently low cortisol levels, a low-dose ACTH stimulation test was performed, which showed appropriate rise in cortisol. His 17-hydroxyprogesterone level was 0.5 ng/mL and 11-deoxycorticosone level was 22 ng/dL, both appropriate for age. Interrogation of the aldosterone axis yielded markedly elevated aldosterone and renin levels of 816 ng/mL/h an...