A neonate has ambiguous genitalia with virilized female external genitalia (clitoromegaly, labial fusion). On day 10, the baby develops hyponatremia (Na 120 mEq/L), hyperkalemia, and hypotension. Serum 17-OH progesterone is markedly elevated. What is the MOST likely diagnosis?
- A 11-beta hydroxylase deficiency (CAH)
- B 21-hydroxylase deficiency (CAH), salt-wasting form ✓
- C True hermaphroditism
- D Androgen insensitivity syndrome
Correct answer: B. 21-hydroxylase deficiency (CAH), salt-wasting form
Explanation
This is the classic presentation of salt-wasting 21-hydroxylase deficiency, the most common form of Congenital Adrenal Hyperplasia (CAH), accounting for ~75% of all CAH. Deficiency of 21-hydroxylase blocks cortisol and aldosterone synthesis, causing accumulation of precursors that are shunted to androgen synthesis. In 46,XX females, this causes virilization of external genitalia. Salt-wasting crisis (hyponatremia, hyperkalemia, hypotension) occurs in weeks 2-4 of life. Elevated 17-OH progesterone is the diagnostic marker. Treatment: hydrocortisone + fludrocortisone.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.