A 16-year-old girl with primary amenorrhea has the following features. What is the most probable diagnosis? ● Normal stature ● Thelarche – absent ● FSH, LH – high ● Karyotype – 46 XX

Explanation

## Correct Answer: C. Gonadal dysgenesis Gonadal dysgenesis (pure gonadal dysgenesis or Swyer syndrome) is the diagnosis here. The key discriminator is the **46,XX karyotype with normal stature, absent thelarche, and elevated FSH/LH**. In gonadal dysgenesis, the ovaries fail to develop properly despite a normal female karyotype—they are replaced by fibrous streaks. This results in primary amenorrhea, absent secondary sexual characteristics (thelarche), and markedly elevated gonadotropins (FSH and LH) due to loss of negative feedback from non-functional gonads. The normal stature rules out Turner syndrome (45,X), which typically presents with short stature. The high gonadotropins indicate primary gonadal failure (hypergonadotropic hypogonadism), not central hypogonadism. Kallmann syndrome presents with low gonadotropins (hypogonadotropic hypogonadism) and anosmia. Testicular feminizing syndrome occurs in 46,XY individuals with androgen insensitivity. In India, gonadal dysgenesis is an important cause of primary amenorrhea in adolescent girls presenting to gynecology clinics, and diagnosis requires karyotyping and pelvic ultrasound showing streak gonads or absent ovaries. ## Why the other options are wrong **A. Turner syndrome** — Turner syndrome (45,X or mosaicism) classically presents with short stature, webbed neck, and cardiac/renal anomalies. This patient has **normal stature**, which is the key exclusion criterion. While Turner syndrome does cause primary amenorrhea and elevated gonadotropins, the karyotype is 46,XX here, not 45,X. NBE uses short stature as the discriminator to trap students who know Turner causes amenorrhea. **B. Kallmann syndrome** — Kallmann syndrome is a form of **hypogonadotropic hypogonadism** caused by GnRH deficiency, presenting with low FSH and LH levels, not elevated ones. This patient has **high FSH and LH**, indicating primary gonadal failure, not central hypogonadism. Kallmann also presents with anosmia (olfactory nerve hypoplasia). The elevated gonadotropins here rule out any central cause. **D. Testicular feminizing syndrome** — Testicular feminizing syndrome (androgen insensitivity syndrome) occurs in **46,XY individuals**, not 46,XX. This patient has a normal female karyotype. Additionally, AIS typically presents with absent uterus and fallopian tubes (müllerian agenesis) and normal-to-high testosterone levels. The 46,XX karyotype is the absolute exclusion criterion for this diagnosis. ## High-Yield Facts - **Gonadal dysgenesis (Swyer syndrome)** = 46,XX karyotype + streak gonads + primary amenorrhea + normal stature + elevated FSH/LH (primary gonadal failure). - **Hypergonadotropic hypogonadism** (high FSH/LH) indicates primary gonadal failure; **hypogonadotropic hypogonadism** (low FSH/LH) indicates central/hypothalamic-pituitary dysfunction. - **Turner syndrome** requires 45,X karyotype or mosaicism; gonadal dysgenesis is 46,XX—karyotype is the discriminator. - **Kallmann syndrome** = GnRH deficiency + anosmia + low gonadotropins; gonadal dysgenesis = streak gonads + high gonadotropins. - **Diagnosis of gonadal dysgenesis**: karyotype (46,XX) + pelvic ultrasound (streak gonads or absent ovaries) + elevated FSH/LH + normal müllerian structures. ## Mnemonics **HIGH vs LOW gonadotropins in amenorrhea** **HIGH FSH/LH** = Primary gonadal failure (ovarian problem) → Gonadal dysgenesis, Turner, POI. **LOW FSH/LH** = Central hypogonadism (brain problem) → Kallmann, hypothalamic amenorrhea. Use: When you see elevated gonadotropins, think ovary; when low, think brain. **Karyotype clue in primary amenorrhea** **46,XX + amenorrhea + high FSH** → Gonadal dysgenesis or POI. **45,X + amenorrhea + short stature** → Turner. **46,XY + amenorrhea + absent uterus** → AIS. Use: Karyotype is the first filter—it eliminates 2/3 of wrong answers. ## NBE Trap NBE pairs "elevated gonadotropins" with Turner syndrome to trap students who know Turner causes amenorrhea but forget that Turner requires 45,X karyotype and short stature. The normal stature and 46,XX karyotype are the discriminators. ## Clinical Pearl In Indian adolescent gynecology clinics, a 16-year-old girl with primary amenorrhea, normal height, and absent breast development should trigger karyotyping immediately. If 46,XX with high FSH/LH, pelvic ultrasound will show streak gonads or absent ovaries, confirming gonadal dysgenesis. Hormone replacement therapy (estrogen + progesterone) is needed for pubertal induction and long-term bone health. _Reference: DC Dutta's Textbook of Gynaecology (Ch. Amenorrhea); Harrison's Principles of Internal Medicine (Ch. 405, Disorders of Sex Development)_