The neurologic development of 90 patients with persistent hyperinsulinemic hypoglycemia was studied retrospectively at Hospitalier Universitaire Necker-Enfants Malades, Paris, France. Treatment was surgical in 63 and medical in 27. Of 54 neonates, 8 were treated medically and 46 surgically. Of 36 with infancy-onset hyperinsulinism, 19 were treated medically and 17 had pancreatectomy. Development was normal in 74%. Severe mental retardation occurred in 8% of patients, and intermediate psychomotor disability in 18%. Epilepsy occurred in 18% of the total (in 24% of 54 neonates and 8% of 36 infants). The incidence of epilepsy was 7% among those with normal mental development and 57% in the severely retarded, at a mean follow-up age of 8 years. Microcephaly occurred in 10% of normal and 57% of severely retarded children. Neonatal onset was the main risk factor for severe retardation or epilepsy. Patients treated medically were less severely affected than those treated surgically. The outcome was not different in patients with diffuse and focal adenomatous hyperplasia with hyperinsulinism. 
COMMENT. Hyperinsulinism in infancy causes recurrent episodes of profound hypoglycemia, often <1 mmol/L, with diverse neurologic sequelae, including psychomotor retardation, learning disability, seizures, and microcephaly. Neonatal onset is associated with more complications and a greater need for surgical treatment. Early diagnosis and onset in infancy result in a slightly better prognosis.
In contrast to the frequent risk of mental impairment in neonates and infants with hyperinsulinemic hypoglycemia, young adults with insulin dependent diabetes and recurrent episodes of hypoglycemia have either a mild or negligible risk of cognitive impairment. 
Offspring of diabetic Japanese mothers are at increased risk of lowered IQ scores at 3 years of age . The risk of hypoglycemic brain damage is related inversely to the age of the patient. (See Progress in Pediatric Neurology III, 1997;p311).