Congenital adrenal hyperplasia — structured clinical encounter

Station brief (candidate)

You are the paediatric registrar. A term male infant who passed his newborn bloodspot screen and was well at discharge returns at two weeks of age with three days of poor feeding and vomiting, and is now lethargic and mottled. The team asks you to make the diagnosis, deliver the immediate resuscitation, arrange the investigations, and speak with the parents. You have 12 minutes with the team and 5 minutes for examiner discussion. [4]

Information available on request

• Term male infant, normal vaginal delivery, genitally normal at birth, passed the day-2 bloodspot screen, well at discharge. [8]
• Day 14: poor feeding, vomiting, lethargy, mottled peripheries, capillary refill 4 seconds; weight down 12 percent from birth. [4]
• Sodium 122, potassium 6.8, glucose 1.9, capillary pH 7.24, base excess minus 10. [4]
• No family history of endocrine disease; parents are anxious and ask whether the screen should have caught it. [8]

Tasks

1. State the most likely diagnosis and the bedside and biochemical features that support it. [4]
2. Deliver the immediate first-hour resuscitation, naming the key drug, its dose and route, and the principle governing its timing. [4]
3. Outline the confirmatory investigation bundle and explain why the definitive test does not delay treatment. [9]
4. Communicate the situation, the reason a passed screen did not prevent this, and the safety-net to the parents in plain language. [8]

Marking anchors

Must-hit

• Recognises classic salt-wasting 21-hydroxylase deficiency until proven otherwise, from the genitally normal male who collapses at one to three weeks with hyponatraemia, hyperkalaemia, hypoglycaemia and acidosis — the classic missed presentation. [4]
• Gives hydrocortisone intravenously 25 mg stat then 50 to 100 mg per square metre per day, with 10 to 20 mL per kg isotonic saline to restore perfusion, treats the hypoglycaemia, and covers sepsis — before the confirmatory 17-hydroxyprogesterone returns, because the test confirms but does not treat. [4]
• Sends serum 17-hydroxyprogesterone, ACTH, plasma renin, aldosterone, androgens, a karyotype and CYP21A2 molecular testing, and arranges endocrinology and a stress-dose plan. [9]

Merit

• Explains that hydrocortisone at stress doses has enough mineralocorticoid activity that fludrocortisone is not needed in the acute phase, and that hyperkalaemia usually corrects as volume, cortisol and aldosterone activity are restored. [4]
• Counsels the parents in plain language: the screen catches most but not all cases, the boy had no genital clue, and the plan is to replace cortisol and aldosterone with a home emergency injection. [8]
• Places the case in context: newborn screening detects most classic cases but misses a real minority, so a passed screen never lowers the threshold to investigate a vomiting neonate. [5] [8]

Fail

• Treats the collapse as sepsis or pyloric stenosis alone, with fluids and antibiotics and no hydrocortisone, while the adrenal crisis deepens. [4]
• Waits for the 17-hydroxyprogesterone result before giving hydrocortisone, delaying the one treatment that can restore the cortisol and aldosterone deficiency. [4]
• Is falsely reassured by the passed screen and the normal early course, and fails to escalate. [8]