Hyperinsulinaemic hypoglycaemia is a common cause of persistent severe hypoglycaemia, and is associated with long term neurodisability and epilepsy. Can be congenital, due to unregulated beta cell function (used to be called nesidioblastosis), else secondary to various other conditions eg:

• Maternal diabetes mellitus
• Birth asphyxia
• IUGR
• Beckwith Wiedemann Syndrome – about 50% are affected, usually transiently
• Inborn error of metabolism eg glycosylation disorder

Can present with severe hypoglycaemia in the newborn period despite good oral intakes, else more insidiously in infancy and childhood. No ketones of course – cf ketotic hypoglycaemia.  Macrosomia (+/- hypertrophic cardiomyopathy and hepatomegaly) is a feature of fetal hyperinsulinism but is not always present, otherwise typical features of hypoglycaemia may be seen, including seizures.

Cases secondary to IUGR/asphyxia tend to be transient, settling within a few days, but some have persistent symptoms for months before suddenly resolving!

Recessive defects in sulphonylurea receptor probably most common cause.  Fasting or exertion are the usual triggers, but postprandial symptoms may reflect dumping syndrome (usually secondary to gastro-oesophageal surgery) or else hyperammonaemic hyperinsulinism (glutamate dehydrogenase disorder – the high ammonia of 100-200 is persistent but asymptomatic). A form of exercise induced hyperinsulinism exists that requires exercise testing to diagnose.

Insulinoma is more likely in later childhood. Can be part of a multiple endocrine neoplasia syndrome type 1 (ask family history).

Raised plasma hydroxybutyrylcarnitine and urinary 3-hydroxyglutarate are diagnostic of Hydroxy AcylCoA Dehydrogenase (HADH) deficiency.

Management aims to achieve normal glucose levels, using Carbohydrate supplemented oral feeds plus IV fluids. A central line may be needed to give concentrated dextrose solutions, esp if chubby. Glucagon can be given IM in an emergency but may lead to paradoxical insulin release. Glucagon and/or octreotide can be given as infusions in resistant cases.

For ongoing treatment, diazoxide acts on K-ATP channels in beta cells. Chlorthiazide is synergistic in the neonatal period. Hypertrichosis is the main side effect of diazoxide. Some rare gene defects are resistant to Diazoxide! Feeding probs esp GORD common, partly due to all the NG/IV feeding.

[Kapoor, Arch Dis Child 2009 PMID 19193661]