## Secondary Amenorrhea: Low FSH/LH Pattern **Key Point:** Low FSH and low LH in secondary amenorrhea indicate **hypogonadotropic hypogonadism** — pathology at the level of the **hypothalamus or pituitary**, not the ovary. ### Interpretation of Hormonal Pattern **FSH 2 mIU/mL and LH 1 mIU/mL (both LOW):** - Indicates failure of GnRH secretion or pituitary gonadotropin synthesis/release - The ovaries are intact and capable of responding to gonadotropins, but are not being stimulated ### Three-Tier Classification of Secondary Amenorrhea | Tier | FSH/LH Status | Location of Pathology | Common Causes | | --- | --- | --- | --- | | **Hypogonadotropic** (Tier 1) | **Low FSH, Low LH** | Hypothalamus or Pituitary | Hypothyroidism, hyperprolactinemia, pituitary adenoma, functional hypothalamic amenorrhea (stress, weight loss, excessive exercise), Sheehan syndrome | | **Eugonadotropic** (Tier 2) | Normal FSH, Normal LH | Uterus or Cervix (Müllerian pathology) | Asherman syndrome, cervical stenosis, uterine scarring | | **Hypergonadotropic** (Tier 3) | **High FSH, High LH** | Ovary (Gonadal failure) | Premature ovarian insufficiency (POI), ovarian dysgenesis, chemotherapy/radiation damage | **Mnemonic:** **HypoGT = Hypothalamus/Pituitary** — when gonadotropins are **hypo**low, the problem is **upstream** at the hypothalamus or pituitary. **High-Yield:** The negative beta-hCG rules out pregnancy. The low gonadotropins point to a central (CNS) cause, not a peripheral (ovarian) cause. **Clinical Pearl:** Common causes of hypogonadotropic amenorrhea include: - Functional hypothalamic amenorrhea (stress, weight loss, excessive exercise) - Hyperprolactinemia (dopamine agonist deficiency) - Hypothyroidism (elevated TRH suppresses GnRH) - Pituitary adenomas (mass effect or prolactin secretion) - Sheehan syndrome (postpartum pituitary necrosis)
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