A 22-year-old woman presents with primary amenorrhea. On examination, she is 165 cm, has normal female secondary sexual characteristics (Tanner Stage 5 breast and pubic hair), but on pelvic examination has a blind-ending vagina and no palpable uterus. Karyotype returns as 46, XY. Serum testosterone is 45 nmol/L (normal male range 10–35 nmol/L). LH is elevated. What is the MOST likely diagnosis?
- A Swyer syndrome (46,XY complete gonadal dysgenesis) — gonadal streak, low testosterone
- B Complete androgen insensitivity syndrome (CAIS, testicular feminization) ✓
- C 17α-hydroxylase deficiency with 46,XY disorder of sex development
- D 5α-reductase deficiency with incomplete virilization
Explanation
Complete androgen insensitivity syndrome (CAIS) presents with: 46,XY karyotype, female phenotype with complete Tanner Stage 5 feminization (because testosterone cannot act on androgen receptors), absent uterus and fallopian tubes (because MIS/AMH from testicular Sertoli cells causes Müllerian regression), blind-ending vagina, and markedly elevated testosterone in the male-normal or supranormal range (because high LH drives testicular testosterone production, but it cannot act on receptors). Swyer syndrome (A) has 46,XY with streak gonads, female phenotype, but LOW testosterone and requires estrogen replacement. 17α-hydroxylase deficiency (C) presents with 46,XY and low sex steroids (hypertension and hypokalemia). 5α-reductase deficiency (D) presents with ambiguous genitalia at birth and virilization at puberty, not complete female phenotype.
Reference: Shaw's Textbook of Gynaecology, 17th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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