The diagnosis of hyperinsulinism in a child in the absence of hyperinsulinemia

This report concerns a 15-year-old Japanese girl with hyperinsulinism whose fasting serum immunoreactive insulin (IRI) levels were invariably within normal range. She developed frequent seizures in association with brief fasting at 9 months of age. The anticonvulsant therapy was instituted without benefit. At 5 years of age, she was admitted to our hospital for evaluation of hypoglycemia. Despite profound hypoglycemia her basal serum IRI levels remained normal, and various endocrine tests failed to demonstrate hyperinsulinemia unequivocally. Diagnosis of hyperinsulinism was suspected by consistently lowered serum non-esterified fatty acid (NEFA) and lack of ketonuria during hypoglycemia, and was confirmed by a dramatic response to diazoxide therapy. During the past 9 years, she has remained asymptomatic with fasting blood sugar of 74-87mg/dl on diazoxide (2.5mg/kg/day).