Congenital Hyperinsulinemia: A Hidden Cause of Persistent Hypoglycemia in Newborns

Persistent, recurrent hypoglycemia is considered when the newborn fails to maintain normal blood glucose despite a Glucose Infusion rate (GIR) of 12 mg/kg/min or if stabilization is not obtained after 7 days of medication, warranting high glucose infusion rates to establish euglycemia. Hyperinsulinism is the most prevalent cause of persistent hypoglycemia, but it can be acquired or congenital. We present a 35-week-old male newborn who presented on the day of life (DOL) 7 with symptomatic hypoglycemia (Random Blood Sugar 33mg/dL) in the form of lethargy, reduced oral acceptance, and seizure-like behavior, with repeated hypoglycemic episodes recorded since DOL 1. He started on GIR at 6mg/kg/min and subsequently raised to 10mg/kg/min and then 12 mg/kg/min since the baby's blood glucose levels were not stable. A critical sample was submitted, which revealed plasma insulin levels of 94.2 mIU/L. The baby was subsequently put on diazoxide, hydrocortisone, and octreotide. Once euglycemia was reached by DOL 11, GIR was gradually reduced, and meals were supplemented with dextrose in every feed. By DOL 15, the child was on full orogastric feeds enriched with dextrose and medium chain triglyceride (MCT) oil before being discharged at DOL 30 on injection octreotide. Ultrasonography of the whole abdomen and later F-DOPA PET scan indicated no localized pancreatic disease. The genetic test revealed a heterozygous single-base pair duplication in exon 1 of the KCNJ11 gene, suggesting congenital hyperinsulinism (CHI). The diagnosis process followed a stepwise approach: first, a critical sample was taken to establish hyperinsulinemia; then, all acquired causes were ruled out through history, examination, and investigations; and finally, the diagnosis was clinched using genetic testing.