Examqo › Examqo library › Pediatrics › Growth, development and endocrinology · IMLE
Congenital adrenal hyperplasia (CAH)
In CAH a missing enzyme in cortisol synthesis (95% — 21-hydroxylase) raises ACTH, and the precursors are pushed into androgen production: girls are born with atypical genitalia, and boys look normal until a salt-wasting crisis appears in the second week of life.
Why it matters in the exam
Two cases recur in the exam. The first is a 46,XX newborn with clitoromegaly and fused labia — the test is 17-OHP and the diagnosis is CAH, the most common cause of atypical genitalia in a girl. The second is a 10-day-old infant with vomiting, dehydration, hyponatraemia, hyperkalaemia and hypoglycaemia — an adrenal crisis treated at once with hydrocortisone and fluids.
Other forms are examined too: "non-classic" CAH appearing in a girl with early pubic hair and accelerated growth, or in an adolescent with hirsutism and irregular periods; here basal 17-OHP may be normal and the diagnosis is made with an ACTH stimulation test. 11-beta-hydroxylase deficiency causes virilisation with hypertension and hypokalaemia, because DOC accumulates and acts as a mineralocorticoid.
Treatment in a growing child is hydrocortisone 10–15 mg/m² per day in three doses — not long-acting agents that stop growth — together with fludrocortisone and salt supplements in infancy. During febrile illness or surgery the dose is doubled or tripled, and in crisis hydrocortisone 50–100 mg/m² IV and fluids are given. In Israel CAH is part of newborn screening.
Key points
- 95% of CAH is 21-hydroxylase deficiency.
- Girl — atypical genitalia; boy — salt-wasting crisis in weeks 1–3.
- Diagnosis by 17-OHP; in Israel CAH is in the newborn screen.
- Hydrocortisone 10–15 mg/m² per day, fludrocortisone and salt.
- Stress dosing in illness; in crisis IV hydrocortisone and fluids.
Summary table
| Form | Presentation | Laboratory | Treatment |
|---|---|---|---|
| Classic salt-wasting (21-OH) | Girl: atypical genitalia; boy: crisis in weeks 1–3 | Very high 17-OHP, low sodium, high potassium, high renin | Hydrocortisone, fludrocortisone, salt |
| Classic simple virilising (21-OH) | Virilisation, accelerated growth, advanced bone age | High 17-OHP, normal electrolytes | Hydrocortisone |
| Non-classic (21-OH) | Early pubic hair, hirsutism, acne, irregular periods | 17-OHP after ACTH stimulation | Hydrocortisone according to symptoms |
| 11-beta-hydroxylase deficiency | Virilisation with hypertension | High DOC and 11-deoxycortisol, low potassium, low renin | Glucocorticoid |
| 17-alpha-hydroxylase deficiency | Hypertension, absent puberty; 46,XY under-virilised | Low potassium, low androgens | Glucocorticoid and sex-hormone replacement |
A free exam question
ילד בן 7 שנים סובל בשבועות האחרונים מפוליאוריה ופולידפסיה. מצורפת טבלה של בדיקות העזר (דם ושתן) שנלקחו בו זמנית: ערכי נורמה תוצאה סוג בדיקה 7.45 - pH 7.37 7.35 בדם 28 - HCO3 24.2 meq/l 21 בדם 100 - 70 99 mg/dl גלוקוז ( בדם Glu ) - שלילי ( שתן לקטונים ketones ) 145 - 149 meq/l 135 ( נתרן בדם Na ) 310 mosm/kg > 300 ( אוסמולריות Osm ) הדם - 280 mosm/kg ( אוסמולריות Osm ) השתן איזה מהאבחנות הבאות?יכולה להתאים למצבו (the question as examined, in Hebrew)
- א. Langerhans cell histiocytosis
- ב. Compulsive water drinking
- ג. Congenital adrenal hyperplasia
- ד. Syndrome of inappropriate ADH
In the full version for subscribers
- A simple algorithm
- Memory aid
- Exam traps
- 5 review cards
- Enough for IMLE
The full version is open to subscribers of: Pediatrics, Medical licensing exam (IMLE), Internal medicine, Obstetrics and gynecology, Pediatric surgery.
Subscriber? Read the full topic Plans and prices 25 free questions
Sources
- Endocrine Society Clinical Practice Guideline: Congenital Adrenal Hyperplasia Due to Steroid 21-Hydroxylase Deficiency, 2018 — Newborn screening, diagnosis and glucocorticoid treatment
- Nelson Textbook of Pediatrics, 22nd edition (2024) — Congenital Adrenal Hyperplasia and Related Disorders
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.