Case 2: Hyponatremia and hyperkalemia in a four-week-old boy

Abstract

A four-week-old male infant presented to the emergency department with failure to thrive (360 g below his birth weight), and had a history of poor eating, increased sleeping and irritability over his first month of life. The infant’s family history was significant for polycystic kidney disease in his mother and female relatives. On presentation, his blood pressure was 102/74 mmHg, heart rate was 162 beats/min, respiratory rate was 52 breaths/min, oxygen saturation was 99% and rectal temperature was elevated at 39.4°C. A physical examination revealed a somewhat wasted, nondysmorphic, nontoxic baby with normal male genitalia. The rest of the physical examination was essentially normal. The infant’s bloodwork showed a a sodium concentration of 121 mmol/L, and a potassium concentration of 7.1 mmol/L. (The tests were repeated and found to be accurate.) Capillary gases showed a pH of 7.32, bicarbonate of 13 mmol/L and PCO2 of 26 mmHg. An electrocardiogram was performed, which did not show any abnormalities. His urine test was positive for blood and leukocytes, but negative for nitrites. The initial management included a fluid bolus and initial empirical antibiotic therapy, with intravenous ampicillin and cefotaxime. Kayexalate (sanofi-aventis, Canada) was administered. Other therapies for hyperkalemia were held due to the normal electrocardiogram findings. A full-septic workup was performed, including a lumbar puncture. Fludrocortisone and hydrocortisone were given. The patient was subsequently admitted to the paediatric critical care unit, with a presumed diagnosis of congenital adrenal hyperplasia for correction of electrolyte and fluid balance. Surprisingly, the endocrine workup for presumed congenital adrenal hyperplasia was negative. An ultrasound of the abdomen was performed, which together with one of the other test results helped to make the correct diagnosis.