AKT · Child health/Neonatal & surgical

Congenital adrenal hyperplasia (CAH)

21-hydroxylase deficiency (>90%) — autosomal recessive

Overview

A group of autosomal-recessive enzyme defects of cortisol synthesis; >90% are 21-hydroxylase deficiency. Cortisol ± aldosterone deficiency with shunting of precursors into ANDROGENS. Presents as virilisation and, in the salt-wasting form, a life-threatening neonatal adrenal crisis.

Recognise

Female neonate: virilised/ambiguous genitalia (clitoromegaly, fused labia) with normal internal organs
Male neonate: often normal genitalia → easily missed until salt-wasting crisis
Salt-wasting crisis (~1–3 weeks): vomiting, poor feeding, weight loss, lethargy, shock — HYPONATRAEMIA, HYPERKALAEMIA, hypoglycaemia
Non-salt-wasting / later: precocious puberty, tall child who becomes a short adult, hyperpigmentation

Red flags

Neonatal salt-wasting adrenal crisis — hyponatraemia + hyperkalaemia + hypoglycaemia + shock is a medical emergency

Differentials & how to tell them apart

Pyloric stenosisalso vomiting in early weeks but HYPOchloraemic HYPOkalaemic alkalosis (opposite electrolytes), olive mass

Androgen-secreting / maternal androgensvirilisation without cortisol deficiency or salt-wasting

Other DSD causesdistinguished by 17-OHP, karyotype, imaging

Sepsismimics the crisis — but the Na⁺/K⁺ pattern points to CAH

Investigations

Markedly raised 17-hydroxyprogesterone (the hallmark). U&E (low Na⁺, high K⁺), low glucose, ACTH; karyotype/genetics; pelvic USS for internal organs in ambiguous genitalia. (Not on the routine UK blood-spot panel.)

Management

Crisis: IV hydrocortisone + IV 0.9% saline/glucose + treat hyperkalaemia; maintenance: hydrocortisone + fludrocortisone

1Salt-wasting crisis: IV hydrocortisone, IV 0.9% saline with glucose, correct hyperkalaemia — resuscitate first.Gate: Hyponatraemia WITH hyperkalaemia + hypoglycaemia in a vomiting neonate → treat as adrenal crisis even before 17-OHP returns
2Maintenance: hydrocortisone + fludrocortisone (+ salt in infancy); MedicAlert; sick-day dosing.
3Virilised female: specialist DSD team, consideration of surgery, psychological support.

Hydrocortisone — glucocorticoid replacement (and IV in crisis); doubled during illness (sick-day rules)

Fludrocortisone — mineralocorticoid replacement in salt-wasting CAH

Salt (sodium chloride) supplements — in infancy for salt-wasters

Key points

The classic trap: a vomiting neonate where the electrolytes (high K⁺, low Na⁺) point to CAH, vs pyloric stenosis where they are the mirror image (low K⁺, alkalosis). Sick-day rules and emergency hydrocortisone are lifelong.

Monitor & prognosis

Growth, bone age, 17-OHP/androgens, U&E, blood pressure; sick-day adherence.

Good with replacement + crisis prevention; crises are life-threatening if missed.

Source: NICE CKS / BNF for Children (adrenal insufficiency); specialist endocrinology