A 24-year-old woman presents with secondary amenorrhea of 6 months' duration. She has a history of irregular menses since menarche. Serum FSH, LH, and prolactin are normal. Pelvic ultrasound shows multiple small cysts in both ovaries. What is the most common cause of secondary amenorrhea in this clinical presentation?

Explanation

## Clinical Diagnosis The clinical and investigational findings point to a single diagnosis: - Secondary amenorrhea (previously regular or irregular menses) - History of irregular menses since menarche (chronic anovulation) - Normal FSH, LH, and prolactin (rules out hypogonadism and hyperprolactinemia) - Polycystic ovaries on ultrasound (multiple small cysts bilaterally) ## Polycystic Ovary Syndrome (PCOS) **Key Point:** PCOS is the most common endocrine disorder in reproductive-age women and the most frequent cause of secondary amenorrhea due to anovulation. **High-Yield:** PCOS accounts for approximately 70–80% of anovulatory amenorrhea and 20–30% of all secondary amenorrhea cases. ## Diagnostic Criteria for PCOS (Rotterdam 2003) Diagnosis requires 2 of 3 criteria: 1. Oligo- or anovulation (irregular/absent menses) 2. Clinical or biochemical hyperandrogenism 3. Polycystic ovaries on ultrasound (≥12 follicles 2–9 mm in at least one ovary) This patient meets criteria 1 and 3. ## Why PCOS is Most Common | Feature | PCOS | Hypothyroidism | Hyperprolactinemia | Asherman | | --- | --- | --- | --- | --- | | **Prevalence in secondary amenorrhea** | 20–30% | 5–10% | 5–10% | 5–15% | | **FSH/LH status** | Normal or ↑LH:FSH ratio | Normal | Normal | Normal | | **Prolactin** | Normal | Normal | ↑ | Normal | | **Ultrasound findings** | Polycystic ovaries | Normal | Normal | Normal endometrium | | **Menses pattern** | Irregular since menarche | Variable | Variable | Sudden cessation | **Clinical Pearl:** The elevated LH:FSH ratio (often >3:1) in PCOS results from increased GnRH pulse frequency, driving preferential LH secretion and relative FSH suppression. This perpetuates anovulation and hyperandrogenism. **Mnemonic:** **PCOS = Polycystic Ovaries + Chronic Anovulation + (usually) Hyperandrogenism** — the triad that defines the syndrome. ## Management Approach 1. Confirm diagnosis with clinical assessment (hirsutism, acne, male-pattern baldness) and free testosterone or androstenedione if hyperandrogenism suspected 2. Screen for metabolic complications (insulin resistance, dyslipidemia, impaired glucose tolerance) 3. First-line treatment: Combined oral contraceptives or progestin-only therapy for cycle regulation 4. Lifestyle modification (weight loss if overweight) improves ovulation and metabolic parameters