Persistent neonatal hypoglycaemia in an infant of a diabetic mother
A 3.9 kg term male infant, born at 39 weeks to a mother with insulin-treated gestational diabetes, is admitted to the postnatal ward. At 10 hours of age he is jittery and his bedside glucose is 1.7 mmol/L. He is fed and rechecked at 30 minutes: 1.5 mmol/L. He receives 2 mL/kg of 10% dextrose intravenously followed by an infusion of 6 mg/kg/min. Glucose values over the next 24 hours remain between 1.6 and 2.2 mmol/L despite escalation to 10 mg/kg/min, and a central line is placed. At 34 hours, before the next increment, a critical sample is taken while glucose is 1.8 mmol/L: insulin 32 pmol/L (reference <10), beta-hydroxybutyrate undetectable, free fatty acids 0.05 mmol/L, cortisol 420 nmol/L, growth hormone 18 mU/L, lactate 1.4 mmol/L, ammonia 42 micromol/L. He is clinically well, feeding, with no dysmorphism.
1. Interpret the critical sample and give the most likely diagnosis with your reasoning.
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The critical sample shows an inappropriate insulin concentration (32 pmol/L) at a glucose of 1.8 mmol/L. In true hypoglycaemia, insulin should be suppressed to near the limit of detection. The suppressed beta-hydroxybutyrate and free fatty acids indicate that insulin is blocking lipolysis and ketogenesis, so alternative fuels are unavailable. Cortisol and growth hormone are appropriately elevated, excluding adrenal insufficiency and growth hormone deficiency; lactate and ammonia are normal, making a metabolic acidosis or urea cycle defect unlikely.
This profile is diagnostic of hyperinsulinism. In an infant of a diabetic mother, transient hyperinsulinism is common, but most cases resolve within days. Persistence at 34 hours with a glucose requirement above 10 mg/kg/min and a critical-sample insulin of 32 pmol/L makes congenital hyperinsulinism the leading diagnosis. The main differential is a focal versus diffuse pancreatic lesion, which has management implications. I would not label it transient without demonstrating that glucose requirements fall and that a controlled fasting study is normal.
2. Outline your immediate management over the next 24 hours, including confirmation of the diagnosis and prevention of complications.
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Stabilise glucose first: keep the central line, continue 10% dextrose and escalate concentration (12.5-15%) via central access rather than fluid volume, aiming for pre-feed glucose >3.5 mmol/L. If hypoglycaemia recurs, give 2 mL/kg 10% dextrose bolus and consider glucagon 0.5 mg IM/SC. Start diazoxide 5-10 mg/kg/day in divided doses once hyperinsulinism is suspected, with monitoring for fluid retention and pulmonary hypertension; add chlorothiazide if oedema. If diazoxide fails, use octreotide 1-5 micrograms/kg/day by infusion or divided doses, watching for necrotising enterocolitis and tachyphylaxis.
Confirm the diagnosis with a supervised fasting study once stable: stop dextrose, fast up to 12-18 hours with hourly glucose and ketones, and take critical samples at glucose <2.6 mmol/L. Send ABCC8 and KCNJ11 sequencing, and consider 18F-DOPA PET if diazoxide-unresponsive to distinguish focal from diffuse disease. Monitor for hypoglycaemic seizures, fluid overload, electrolyte disturbance and feeding problems. Involve paediatric endocrinology and a specialist centre early.
3. What would you discuss with the parents about long-term outlook and follow-up?
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Explain that congenital hyperinsulinism is a disorder of insulin regulation, not diabetes, and that the immediate priority is protecting the brain from recurrent hypoglycaemia. The outlook depends on the type: focal disease is potentially curable by limited pancreatectomy, whereas diffuse disease often requires long-term medication and may need near-total pancreatectomy. After surgery, the child may develop diabetes and exocrine pancreatic insufficiency, so lifelong follow-up is needed. Medical therapy with diazoxide or octreotide may control diffuse disease, but side effects and breakthrough hypoglycaemia require monitoring.
Neurodevelopment is the main long-term concern; recurrent or prolonged hypoglycaemia can cause learning difficulties, epilepsy and visual impairment. Arrange developmental follow-up, hearing and vision checks, and seizure surveillance. Discuss the genetic result: ABCC8/KCNJ11 mutations are usually autosomal recessive but can be dominant with variable penetrance, so parental testing and genetic counselling are important. Give a written hypoglycaemia action plan, supply a glucose meter, and teach the family to check glucose during illness and before feeds. Emphasise that fasting must be avoided and that the child needs a medical alert plan.