13.4 Menopause & Menopausal Hormone Therapy

Women's health in internal medicine encompasses the management of the menopausal transition, evidence-based menopausal hormone therapy (MHT), systematic evaluation of abnormal uterine bleeding, workup of postmenopausal bleeding, and guideline-directed screening for cervical, endometrial, and ovarian malignancies. Mastery of these clinical topics is heavily tested on the ABIM examination.

1. Menopause & Perimenopause

Clinical Definitions & Diagnostic Principles

• Menopause: A permanent cessation of menses diagnosed retrospectively after 12 consecutive months of amenorrhea resulting from the loss of ovarian follicular activity, in the absence of other physiological (lactation, pregnancy) or pathological (thyroid dysfunction, hyperprolactinemia) causes. The average age of natural menopause in the United States is 51.4 years (normal range: 45 to 55 years).
• Premature Ovarian Insufficiency (POI): Loss of normal ovarian function before age 40, characterized by amenorrhea, elevated serum FSH (>25-40 IU/L on 2 occasions >1 month apart), and hypoestrogenism. POI mandates systemic hormone replacement therapy until at least the median age of natural menopause (~51 years) to preserve bone mineral density and reduce cardiovascular mortality.
• Perimenopause (Menopausal Transition): The symptomatic period preceding menopause characterized by menstrual irregularity (>7 days difference in cycle length between consecutive cycles in early transition; >=60 days of amenorrhea in late transition), vasomotor symptoms, insomnia, and mood changes.

ABIM Diagnostic Pearl — Laboratory Testing in Menopause:

• In a woman aged >45 years presenting with classic irregular menses and vasomotor symptoms, routine measurement of serum FSH, LH, estradiol, or anti-Müllerian hormone (AMH) is NOT recommended or required for diagnosis.
• Because ovarian follicular development fluctuates dramatically during perimenopause, single hormone measurements are erratic, misleading, and do not change management.
• Laboratory testing (TSH, prolactin, hCG, FSH) is indicated only in women <45 years presenting with secondary amenorrhea to rule out POI, prolactinoma, thyroid disease, or pregnancy.

Symptom Complexes

1. Vasomotor Symptoms (VMS):
   • Hot flashes and night sweats affect up to 80% of menopausal women, lasting an average of 7 to 9 years.
   • Pathophysiology: Estrogen withdrawal alters hypothalamic thermoregulation. Loss of estrogen negative feedback leads to hypertrophy and hyperactivity of Kisspeptin-Neurokinin B-Dynorphin (KNDy) neurons in the infundibular nucleus of the hypothalamus, which excessively stimulate the median preoptic thermoregulatory center, triggering inappropriate peripheral vasodilation and diaphoresis.
2. Genitourinary Syndrome of Menopause (GSM / Vulvovaginal Atrophy):
   • Affects >50% of postmenopausal women and is progressive without treatment.
   • Pathophysiology: Estrogen receptors in the vulva, vagina, urethra, and bladder trigone become depleted. Hypoestrogenism causes loss of vaginal rugae, thinning of the vaginal stratified squamous epithelium, loss of cellular glycogen, depletion of protective Lactobacillus species, elevation of vaginal pH (>5.0), and loss of connective tissue elasticity.
   • Presentation: Vaginal dryness, burning, dyspareunia, vulvar pruritus, urinary urgency, frequency, dysuria, and recurrent urinary tract infections.

2. Menopausal Hormone Therapy (MHT)

Indications & The "Window of Opportunity" Timing Hypothesis

• Approved Indications:
  1. Moderate-to-severe vasomotor symptoms (hot flashes, night sweats)
  2. Prevention of postmenopausal osteoporosis and fragility fractures in symptomatic women at elevated fracture risk
  3. Moderate-to-severe symptoms of vulvovaginal atrophy / GSM
• The Timing Hypothesis (NAMS / The Menopause Society & WHI Data):
  • In healthy symptomatic women who are <60 years of age OR within 10 years of menopause onset, the benefits of systemic MHT generally outweigh the risks (favorable cardiovascular profile, reduced all-cause mortality, and decreased fracture incidence).
  • Initiating systemic MHT in women >60 years of age or >10 to 20 years post-menopause carries an unfavorable risk profile with increased risks of coronary heart disease, stroke, venous thromboembolism, and dementia.
  • Critical Rule: Systemic MHT should NEVER be initiated for the primary or secondary prevention of cardiovascular disease or dementia.

Regimen Selection & Rules of Administration

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|                         MENOPAUSAL HORMONE THERAPY (MHT) RULES                          |
+-----------------------------------------------------------------------------------------+
| 1. WOMEN WITH AN INTACT UTERUS:                                                         |
|    - MUST receive Estrogen PLUS Progestogen (or Bazedoxifene)                           |
|    - Unopposed systemic estrogen stimulates endometrial proliferation and increases   |
|      endometrial adenocarcinoma risk 8- to 10-fold!                                    |
|    - Preferred Progestogen: Micronized Progesterone (100 mg daily continuous or        |
|      200 mg daily cyclic for 12-14 days/month) due to lower VTE/breast cancer risk      |
|    - TSEC Alternative: Conjugated Estrogens 0.45 mg + Bazedoxifene 20 mg (SERM)         |
+-----------------------------------------------------------------------------------------+
| 2. WOMEN WITH PRIOR HYSTERECTOMY:                                                       |
|    - Receive Estrogen-Alone Therapy (ET)                                                |
|    - Progestogen is NOT required because there is no uterus / no endometrial cancer risk|
+-----------------------------------------------------------------------------------------+
| 3. ROUTE OF ESTROGEN ADMINISTRATION:                                                    |
|    - Transdermal Estradiol (patch 0.025-0.1 mg/d, gel, spray): PREFERRED in women with |
|      hypertension, obesity, hypertriglyceridemia, diabetes, smoking, or moderate VTE   |
|      risk. Bypasses hepatic first-pass metabolism, does not increase clotting factors   |
|      (prothrombin, factor VII) or CRP, and does not elevate triglycerides.             |
|    - Oral Estrogens: Increases hepatic coagulation factor synthesis and triglycerides.  |
+-----------------------------------------------------------------------------------------+
| 4. ISOLATED GENITOURINARY SYNDROME OF MENOPAUSE (GSM):                                  |
|    - First-line: Low-Dose Local Vaginal Estrogen (cream 0.01%, 10 mcg tablet, ring)    |
|    - Minimal systemic absorption; does NOT increase VTE or breast cancer risk           |
|    - Does NOT require opposing progestin therapy even with an intact uterus!            |
+-----------------------------------------------------------------------------------------+

Non-Hormonal Pharmacotherapy for Vasomotor Symptoms

For women with absolute contraindications to estrogen (breast cancer, prior VTE, stroke) or who decline hormonal therapy:

1. Fezolinetant (Veozah, 45 mg PO daily):
   • First-in-class selective Neurokinin 3 (NK3) receptor antagonist.
   • Directly blocks neurokinin B binding on hypertrophied hypothalamic KNDy neurons, restoring normal thermoregulatory center signaling without hormone exposure.
   • Monitoring: Baseline serum hepatic transaminases (ALT, AST) and total bilirubin; repeat at 3, 6, and 9 months. Discontinue if ALT/AST >=3x ULN.
2. SSRIs & SNRIs:
   • Venlafaxine ER (37.5-75 mg daily), Desvenlafaxine (50 mg daily), Escitalopram (10-20 mg daily), or Paroxetine (7.5 mg daily).

   • CRITICAL BOARD CONTRAINDICATION — Tamoxifen & CYP2D6:

     • Tamoxifen is a prodrug requiring hepatic CYP2D6 bioactivation into its active anti-estrogenic metabolite, Endoxifen.
     • Potent CYP2D6 inhibitors—specifically Paroxetine and Fluoxetine—inhibit this conversion, significantly lowering endoxifen levels and increasing breast cancer recurrence.
     • In breast cancer patients on Tamoxifen, Paroxetine and Fluoxetine are strictly contraindicated. Use Venlafaxine, Desvenlafaxine, or Gabapentin instead.

3. Gabapentin (300 to 900 mg PO at bedtime):
   • Modulates voltage-gated calcium channels in hypothalamic thermoregulatory pathways; particularly beneficial for nocturnal hot flashes and comorbid insomnia.
4. Clonidine (0.05-0.1 mg PO BID or weekly patch):
   • Central alpha-2 adrenergic agonist; reduces central noradrenergic surge. Limited by side effects (sedation, dry mouth, orthostatic hypotension, rebound hypertension).

Absolute Contraindications to Systemic MHT

• Active, past, or suspected breast cancer or estrogen-dependent neoplasia (endometrial cancer)
• Unexplained, undiagnosed abnormal uterine bleeding
• Active or prior venous thromboembolism (DVT or PE) or known thrombophilia
• Active or recent arterial thromboembolic disease (myocardial infarction, stroke, TIA)
• Severe active liver disease or acute hepatic impairment
• Porphyria cutanea tarda