Congenital adrenal hyperplasia — branching viva

Station opening

Examiner: "Tell me the single bedside concept that frames every neonate with suspected congenital adrenal hyperplasia, and why it matters." [1]

Strong candidate (must-hit)

• The concept is the enzyme block: a 21-hydroxylase deficiency starves the body of cortisol (and usually aldosterone) and shunts the spare steroid precursors into androgens. At the bedside that means three things at once — a salt-wasting crisis, cortisol-deficient shock, and virilisation. It matters because the 46,XX infant is flagged by her genitalia while the 46,XY infant has no genital clue and collapses at one to three weeks, and the window to recognise and treat is narrow. [1]

Weak candidate

• "We measure 17-hydroxyprogesterone on the bloodspot." [1]

Branch A — The genitally normal male who collapses

Examiner: "A term boy, genitally normal, passed his screen, now vomiting and mottled at two weeks with sodium 122, potassium 6.8 and glucose 1.9. What is the diagnosis, your immediate drug and its dose, and the principle governing its timing?" [4]

Strong

• Diagnoses classic salt-wasting 21-hydroxylase deficiency until proven otherwise, because a genitally normal male who salt-wastes at one to three weeks — with hyponatraemia, hyperkalaemia, hypoglycaemia and acidosis — is the classic missed presentation. The immediate drug is hydrocortisone intravenously 25 mg stat then 50 to 100 mg per square metre per day, alongside 10 to 20 mL per kg isotonic saline to restore perfusion. The principle is to give the hydrocortisone before the confirmatory 17-hydroxyprogesterone returns: the test confirms, it does not treat, and waiting risks irreversible shock. [4]

Weak

• "It is probably pyloric stenosis — I would rehydrate and arrange an ultrasound." [4]

Branch B — The virilised 46,XX newborn

Examiner: "A newborn has clitoromegaly, posterior labial fusion and a single perineal opening. No gonad is palpable and ultrasound shows a uterus. What is the diagnosis, the key exam finding, and the confirmatory work-up?" [10]

Strong

• Diagnoses virilising congenital adrenal hyperplasia, the commonest cause of 46,XX disorder of sex development. The key exam finding is the absence of a palpable gonad — a palpable gonad means testicular tissue and shifts the diagnosis toward a 46,XY disorder, whereas no gonad with a uterus and virilisation fits 46,XX CAH. Confirms with markedly elevated serum 17-hydroxyprogesterone, high ACTH, high renin, low aldosterone, elevated androstenedione and testosterone, a karyotype, and CYP21A2 molecular testing. [9] [10]

Weak

• "It is ambiguous genitalia — I would refer to urology for surgery." [10]

Branch C — The screen and its pitfalls

Examiner: "The boy in Branch A passed his newborn bloodspot screen. How sensitive is the screen, and what does that imply for a vomiting neonate?" [8]

Strong

• The 17-hydroxyprogesterone screen detects most but not all classic cases; it misses a real minority, over-represented by simple-virilising disease and by infants whose salt-wasting declares after the screen, and it over-flags preterm and sick infants whose 17-OHP is physiologically high. Second-tier liquid chromatography-tandem mass spectrometry and increasingly molecular testing refine it. The implication is that a passed screen never lowers the threshold to send a serum 17-OHP in any vomiting or collapsing neonate. [5] [8]

Weak

• "The screen is reliable — if it was normal, this cannot be CAH." [8]

Branch D — The sick child on treatment

Examiner: "A school-age child with known CAH has a fever and is now vomiting. What do you do, and what is the family's home plan?" [4]

Strong

• Recognises an adrenal crisis in a treated child who cannot mount a cortisol response to stress and cannot absorb oral medication. Give parenteral hydrocortisone immediately — intramuscularly if no access — and fluid resuscitation, then admit. The family's home plan is a stress-dose protocol: two to three times the usual hydrocortisone for illness, and a parent-held intramuscular hydrocortisone injection given before coming to hospital when the child vomits or collapses, supported by a MedicAlert identifier and a school care plan. [4]

Weak

• "Give paracetamol and encourage oral fluids, and review in the morning." [4]

Close

Examiner: "Summarise your approach to congenital adrenal hyperplasia in one sentence." [1]

Strong

• "I hold the enzyme block in mind — salt-wasting, cortisol deficiency and androgen excess — send a 17-hydroxyprogesterone in any neonate who vomits or collapses or who is virilised, resuscitate with volume and parenteral hydrocortisone before the result, then replace hydrocortisone, fludrocortisone and sodium with a stress-dose and emergency-injection plan that travels with the child." [1] [4]