Paediatric Endocrinology, Diabetes and Metabolic Disorders
This domain covers new-onset type 1 diabetes and diabetic ketoacidosis, disorders of growth and puberty, congenital adrenal hyperplasia and the acute presentation of inherited metabolic disease. Examiners favour the first hour of management, where most harm is done.
Diabetic ketoacidosis
Diagnosis: hyperglycaemia, ketones, pH below 7.3 or bicarbonate below 18 mmol/L. Management principles: correct shock with 10-20 mL/kg isotonic saline, then rehydrate slowly over 48 hours using a calculated deficit plus maintenance; start insulin at 0.05-0.1 U/kg/hour at least one hour after fluids begin; never give a bolus. Add dextrose when glucose falls below about 14-15 mmol/L. Cerebral oedema is the feared complication: headache, bradycardia, hypertension, falling consciousness; treat with hypertonic saline or mannitol and reduce fluid rate.
Growth and puberty
Growth hormone deficiency presents with severe short stature, low growth velocity and delayed bone age; investigate with IGF-1 and stimulation testing. Precocious puberty is breast or testicular development before 8 years in girls and 9 years in boys; a boy with precocious puberty needs imaging of the central nervous system. Delayed puberty is absence of signs by 14 years.
Congenital adrenal hyperplasia
21-hydroxylase deficiency produces virilisation in girls, salt wasting with hyponatraemia, hyperkalaemia and shock in the second to third week. Newborn screening by 17-hydroxyprogesterone; treat with hydrocortisone and fludrocortisone plus sodium chloride.
Metabolic disorders
Unexplained neonatal encephalopathy, acidosis, hyperammonaemia or hypoglycaemia should prompt a metabolic screen: ammonia, lactate, blood gases, amino acids, organic acids and acylcarnitines. Take the critical sample during hypoglycaemia (insulin, cortisol, growth hormone, free fatty acids, ketones, lactate) before treatment.
Worked example
A 10-year-old with polyuria, vomiting and glucose 28 mmol/L, pH 7.05, bicarbonate 8 mmol/L and capillary ketones 6 mmol/L. He is in severe DKA. Give 10 mL/kg saline for shock, then rehydrate over 48 hours; start insulin infusion one hour after fluids; monitor hourly glucose, electrolytes and neurological status; potassium replacement once potassium is below 5.5 mmol/L and urine output is established.
Traps
Insulin bolus; rapid rehydration; bicarbonate for acidosis; diagnosing diabetes on HbA1c alone in an acutely unwell child; forgetting that potassium falls as insulin drives it intracellularly.