A 24-year-old woman from Mumbai presents with secondary amenorrhea for 6 months. She is a professional dancer with a BMI of 18 kg/m² and reports recent weight loss of 5 kg over 3 months. She denies pregnancy, medications, or systemic illness. Menarche was at age 12, and she had regular cycles until 6 months ago. General examination is unremarkable. FSH is 3.2 mIU/mL (normal 4–12), LH is 2.8 mIU/mL (normal 2–10), prolactin is 12 ng/mL (normal <25), and TSH is 2.1 mIU/L (normal). Pelvic ultrasound shows normal uterus and ovaries with no follicles. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Hypothalamic Amenorrhea (Functional Amenorrhea) ### Key Features of This Case **Key Point:** Secondary amenorrhea in a lean, athletic woman with recent weight loss, low-normal FSH/LH, normal prolactin, normal TSH, and ultrasound showing normal uterus but absent follicles is diagnostic of hypothalamic amenorrhea due to energy deficit. ### Pathophysiology of Hypothalamic Amenorrhea Energy deficit (from weight loss, excessive exercise, or both) suppresses GnRH secretion, leading to: 1. **Decreased pulsatile GnRH** → Reduced FSH and LH secretion 2. **Anovulation** → No follicular development and no ovulation 3. **Amenorrhea** → Absence of menstrual bleeding 4. **Preserved other hormones** → Prolactin, TSH, and other axes remain normal ### Diagnostic Approach ```mermaid flowchart TD A[Secondary Amenorrhea]:::outcome --> B{Pregnancy test?}:::decision B -->|Positive| C[Pregnancy]:::outcome B -->|Negative| D{TSH, Prolactin?}:::decision D -->|Abnormal| E[Thyroid/Hyperprolactinemia]:::outcome D -->|Normal| F{Pelvic ultrasound?}:::decision F -->|Abnormal| G[Structural/PCOS]:::outcome F -->|Normal uterus, no follicles| H{Weight loss, exercise, stress?}:::decision H -->|Yes| I[Hypothalamic Amenorrhea]:::action H -->|No| J[Investigate further]:::action ``` ### Why This Patient Has Hypothalamic Amenorrhea | Finding | This Patient | Interpretation | |---------|--------------|----------------| | **Weight loss** | 5 kg in 3 months | Energy deficit trigger | | **BMI** | 18 kg/m² (lean) | Low body fat | | **Occupation** | Professional dancer | High energy expenditure | | **FSH/LH** | Low-normal (3.2/2.8) | Suppressed GnRH → low gonadotropins | | **Prolactin** | Normal (12 ng/mL) | Rules out hyperprolactinemia | | **TSH** | Normal (2.1 mIU/L) | Rules out thyroid disorder | | **Ultrasound** | Normal uterus, no follicles | No follicular development (anovulation) | ### Clinical Pearl **Clinical Pearl:** Hypothalamic amenorrhea is a diagnosis of exclusion. It occurs when energy availability (energy intake minus energy expenditure) falls below ~30 kcal/kg fat-free mass/day. Athletes, dancers, and women with restrictive eating patterns are at highest risk. The condition is reversible with weight gain and reduced exercise intensity. ### High-Yield Features Distinguishing from Differentials **vs. Hypothyroidism:** - TSH is normal in hypothalamic amenorrhea; elevated in hypothyroidism - Weight loss (not gain) is typical in hypothalamic amenorrhea **vs. Hyperprolactinemia:** - Prolactin is normal in hypothalamic amenorrhea; elevated in hyperprolactinemia - Galactorrhea would be present in hyperprolactinemia **vs. PCOS:** - PCOS shows multiple small follicles on ultrasound; this patient has no follicles - PCOS typically presents with hirsutism, acne, and elevated androgens (not present here) - FSH/LH ratio in PCOS is typically >2:1; here both are low-normal ### Management 1. **Confirm diagnosis:** Detailed history of weight, exercise, nutrition, stress 2. **Restore energy balance:** Increase caloric intake and/or reduce exercise 3. **Monitor:** Menstrual cycles typically resume within 3–6 months of weight restoration 4. **Bone health:** Screen for osteoporosis if prolonged amenorrhea (>1 year) 5. **Psychological support:** Rule out eating disorders; refer to dietitian and mental health professional if needed ### Mnemonic for Hypothalamic Amenorrhea Triggers **Mnemonic: STRESS = **S**evere weight loss, **T**raining (excessive), **R**estricted eating, **E**nergy deficit, **S**tress (psychological), **S**ystemic illness** — but in this case, weight loss + dancer profile are the key triggers. [cite:Park 26e Ch 8; Jeffcoate's Principles of Gynaecology 8e]