Reproductive Medicine System
Reproductive Medicine
High-yield reproductive medicine for USMLE Step 1/2/3 — breast cancer screening and pharmacology, infertility mechanisms, disorders of sexual differentiation, and the HPG axis. Organized by cluster for exam performance.
Male Reproductive & Breast Cancer
Breast cancer questions on the USMLE are decision-tree problems — risk stratification, screening modality selection, and chemoprevention agent selection (tamoxifen vs raloxifene vs aromatase inhibitors) dominate. Disorders of sexual differentiation test your understanding of androgen physiology: what testosterone does, what DHT does, and which ducts depend on which hormone.
EP357
The Clutch Disorders of Sexual Differentiation Review
- Testosterone → Wolffian duct: Testosterone (from Leydig cells) drives development of epididymis, vas deferens, seminal vesicles. DHT (5α-reductase converts T→DHT) drives external virilization: prostate, external genitalia, male external appearance
- AMH (Müllerian-inhibiting factor): Produced by Sertoli cells; nukes the Müllerian duct → prevents development of fallopian tubes, uterus, cervix, upper vagina in XY individuals
- 5α-reductase deficiency: XY male; internally male (Wolffian intact), externally ambiguous at birth → virilizes at puberty (testosterone surges, partial external development occurs). Testes in inguinal canal or labia
- Congenital adrenal hyperplasia (21-OH deficiency): XX female most common — virilized external genitalia (clitoromegaly, labial fusion) but internal female structures intact. Salt-wasting crisis = hyponatremia + hyperkalemia + hypotension in neonates
- Turner syndrome (45XO): Streak ovaries → hypergonadotropic hypogonadism (high FSH/LH, no negative feedback); coarctation of aorta, horseshoe kidney, bicuspid aortic valve, primary amenorrhea, short stature
- Klinefelter syndrome (47XXY): Male phenotype; small firm testes; ↓ testosterone → ↑ FSH/LH; gynecomastia; infertility; increased breast cancer risk; long extremities
Androgen Physiology — The Core Framework
| Hormone | Source | Action | Target Structure |
|---|---|---|---|
| Testosterone | Leydig cells (LH-stimulated) | Wolffian duct development | Epididymis, vas deferens, seminal vesicles |
| DHT | T → DHT via 5α-reductase in target tissues | External virilization | Prostate, external genitalia, male external appearance |
| AMH (MIF) | Sertoli cells (FSH-stimulated) | Destroys Müllerian duct | Prevents fallopian tubes, uterus, cervix, upper vagina |
| Estrogen | Granulosa cells (FSH-stimulated) | Breast development, uterine growth | Breast tissue, endometrium (Tanner stage) |
| Androgens | Theca cells (LH-stimulated) | Pubic + axillary hair | Hair follicles (both male and female) |
Key Differentiation — CAH Types
21-hydroxylase deficiency (most common CAH): Blocks cortisol AND aldosterone. Results: ↑ androgens → virilization. Salt-wasting (hyponatremia, hyperkalemia) in severe form. XX female = most tested presentation (virilized female).
11β-hydroxylase deficiency: Blocks cortisol only. Aldosterone precursors (11-deoxycorticosterone) accumulate → hypertension. ↑ androgens → virilization. Key differentiator: HTN + virilization = 11β-OH deficiency.
Gonadotropin Patterns in Key Disorders
| Condition | FSH / LH | Estrogen | Reason |
|---|---|---|---|
| Turner syndrome (45XO) | ↑↑ (hypergonadotropic) | ↓↓ | Streak ovaries → no feedback |
| Klinefelter (47XXY) | ↑↑ (hypergonadotropic) | Normal–↑ (gynecomastia) | Seminiferous tubule failure → no feedback |
| Kallmann syndrome | ↓↓ (hypogonadotropic) | ↓↓ | GnRH neuron migration failure + anosmia |
| PCOS | Normal (LH:FSH ratio >2) | Normal | Anovulation without gonadotropin failure |
| Premature ovarian failure | ↑↑ | ↓↓ | Ovarian failure <40 y/o → no feedback |
EP309
The Clutch Breast Cancer Podcast
- Biggest risk factor: Age (but if biopsy-proven atypical ductal hyperplasia is listed alongside age, pick atypical ductal hyperplasia — premalignant disease trumps age as a risk factor)
- BRCA mutations: Annual mammogram + breast MRI starting age 25–30; prophylactic bilateral mastectomy + THBSO (total abdominal hysterectomy + bilateral salpingo-oophorectomy). Linked to BRCA1/2 = DNA repair defects
- Screening rules (USMLE): Age 40+ → mammogram every 1–2 years. Under 30 → ultrasound (denser breast tissue → mammogram less sensitive). Recent negative mammogram (<few months) + new mass → ultrasound next, not repeat mammogram
- Chemoprevention: GAIL risk ≥1.7% → chemoprevention. Premenopausal → tamoxifen (ER antagonist in breast, agonist in bone/uterus → endometrial cancer risk + VTE risk). Postmenopausal → aromatase inhibitor (anastrozole, letrozole, exemestane) — no VTE or endometrial risk
- HER2+ breast cancer: Bad prognosis but targetable. Trastuzumab (anti-HER2 monoclonal Ab) → ADCC killing mechanism; reversible dilated cardiomyopathy. Doxorubicin → irreversible cardiomyopathy (prevent with dexrazoxane). Pre-chemo echo to check EF
- Prognosis: Most important prognostic factor = axillary lymph node involvement (or metastasis). Sentinel lymph node biopsy first → if positive, proceed to axillary dissection (risk of chronic lymphedema → lymphangiosarcoma)
Breast Mass Evaluation Algorithm
| Age | First Step | If Solid Mass | If Cystic Mass |
|---|---|---|---|
| <30 years | Ultrasound | Mammogram + core needle biopsy | Fine needle aspiration; bloody → cytology |
| >30 years | Mammogram | Core needle biopsy for tissue diagnosis | FNA; bloody aspirate → cytology |
| Any age, recent negative mammogram | Ultrasound (even if >30) | Proceed to biopsy despite negative imaging | — |
| Palpable mass, negative mammogram | Biopsy anyway | Never rely on negative imaging if palpable mass | — |
Tamoxifen vs Aromatase Inhibitors — Critical Comparison
Tamoxifen: ER antagonist in breast (good) but ER agonist in uterus (bad → endometrial cancer) and bone (good → reduces osteoporosis). Also causes VTE. Use premenopausal. Limit to 5 years. Stop at menopause.
Aromatase inhibitors (anastrozole, letrozole, exemestane): Block adipose cell aromatase → no estrogen production. No VTE risk. No endometrial cancer risk. Use postmenopausal. Cause hot flashes (estrogen deficiency).
Breast Cancer Subtypes — HY Details
| Type | Presentation | Treatment Pearl |
|---|---|---|
| ER/PR positive | Most common; hormone-driven | Tamoxifen (pre-M) or AI (post-M) |
| HER2 positive | Bad prognosis; targetable | Trastuzumab (reversible cardiomyopathy) |
| Inflammatory breast cancer | Peau d'orange (skin dimpling); high fevers; weeks-long course → not mastitis | Do not mistake for infection |
| DCIS | Ductal carcinoma in situ | Lumpectomy + radiation = mastectomy (same survival, more local recurrence with lumpectomy) |
| Triple negative | No ER, PR, HER2 | Only chemotherapy; worst prognosis |
Nipple Discharge — Differential
Unilateral bloody nipple discharge = intraductal papilloma (most common). Postmenopausal greenish discharge + lymphoplasmacytic infiltrate on biopsy = mammary duct ectasia. Galactorrhea = prolactinoma, antipsychotics, metoclopramide, hypothyroidism.
Contraception & Fertility
Infertility is tested almost entirely through mechanism — if you understand how prolactin, GnRH, FSH, and ovulation interact, you can derive the answer to any infertility vignette without memorizing a list. EP493 delivers 20+ vignette patterns covering prolactinoma, antipsychotics, PCOS, endometriosis, and primary ciliary dyskinesia.
EP493
The Super Clutch Infertility Podcast
- Definition: Infertility = unable to conceive after 12 months unprotected sex. Begin workup at 6 months if age >35. Biggest risk factor = age (if no specific cause listed)
- PCOS: Anovulation → irregular menses → infertility. Hormone levels generally normal (normal gonadotropic amenorrhea). BMI ↑, insulin resistance (acanthosis nigricans), LH:FSH ratio >2. First-line for fertility = clomiphene (SERM)
- Endometriosis: 3 Ds — dysmenorrhea, dyspareunia, dyschezia (painful defecation). Most infertility questions about endometriosis frame it as an infertility question with these 3 symptoms as context clues
- Varicocele: "Bag of worms" on scrotal exam; pampiniform plexus dysfunction → elevated testicular temperature → impaired spermatogenesis (sperm needs 2°C below core temp). Left-sided more common (left gonadal vein → left renal vein at 90° angle)
- Anti-sperm antibodies: After testicular trauma or infection → breakdown of blood-testis barrier → sperm antigens exposed to immune system → antibodies destroy sperm. Normal hormone levels, normal exam = diagnosis of exclusion
- Primary ciliary dyskinesia (Kartagener): Dynein arm mutation → impaired cilia everywhere. Triad: recurrent sinopulmonary infections + bronchiectasis + situs inversus (apex on right). Infertility via impaired fallopian tube cilia + impaired sperm motility. Hearing loss (middle ear cilia)
Infertility Vignette Master Table
| Clinical Clue | Diagnosis | Mechanism | Gonadotropin Pattern |
|---|---|---|---|
| Short stature, low-extremity claudication, primary amenorrhea | Turner syndrome (45XO) | Streak ovaries | Hypergonadotropic hypogonadism |
| BMI 34, acanthosis nigricans, irregular menses every 3–4 months | PCOS | Anovulation | Normal gonadotropic amenorrhea |
| Breastfeeding mother, infertile | Lactation-induced | Prolactin → GnRH suppression | Hypogonadotropic hypogonadism |
| Poor sense of smell + infertility | Kallmann syndrome | GnRH neuron migration failure | Hypogonadotropic hypogonadism |
| Anorexia (low BMI, calluses on fingers) | Anorexia nervosa | HPG axis shutdown (starvation) | Hypogonadotropic hypogonadism |
| Multiple DNCs, infertile, normal hormones | Asherman syndrome | Endometrial stem cell destruction | Normal gonadotropic amenorrhea |
| Testicular trauma, normal exam + hormones | Anti-sperm antibodies | Blood-testis barrier breakdown | Normal |
| CF patient (elevated sweat chloride) | Cystic fibrosis | Male: agenesis of vas deferens; Female: thick cervical mucus | Normal |
| Recurrent sinopulmonary + situs inversus | Kartagener (primary ciliary dyskinesia) | Dynein arm defect → no ciliary beating | Normal |
| Antipsychotic use (risperidone) + infertility | Drug-induced hyperprolactinemia | D2 blockade → tuberoinfundibular pathway → ↑ prolactin | Hypogonadotropic hypogonadism |
Drugs That Cause Hyperprolactinemia → Infertility
- Antipsychotics (especially risperidone) — D2 blockade at tuberoinfundibular pathway
- Metoclopramide (diabetic gastroparesis) — also a D2 blocker
- Verapamil (non-dihydropyridine CCB for angina/arrhythmia) — directly elevates prolactin
- Opioids — chronic use → prolactin elevation
- TRH elevation (hypothyroidism) — TRH is powerful prolactin stimulator → hypothyroidism can cause infertility via prolactin
EP493
Prolactin & HPG Axis Infertility Mechanisms
- MEN1 + infertility: Pituitary prolactinoma in MEN1 (Para-Pan-Pit mnemonic: Parathyroid + Pancreatic neuroendocrine + Pituitary) → hyperprolactinemia → GnRH suppression → infertility. Autosomal dominant
- CKD + infertility: Kidneys clear prolactin → CKD → hyperprolactinemia → HPG axis shutdown → infertility
- Premature ovarian failure: Ovarian failure <40 years old → hypergonadotropic hypogonadism (↑ FSH/LH) + menopausal symptoms (hot flashes). Diagnosed in women under 40 with these findings
- Fallopian tube scarring (PID/TB): Pelvic inflammatory disease or TB → scarring of fallopian tubes → impaired egg transport (cilia can't beat) → infertility. Most common infective cause post-PID
- Male semen quality: Biggest male risk factor (after age) = semen quality (motility, count, morphology). Cryptorchidism → elevated testicular temperature → impaired spermatogenesis
- Hypogonadotropic vs hypergonadotropic: Hypogonadotropic = problem above gonads (hypothalamus/pituitary). Hypergonadotropic = problem at gonad level (streak ovaries, testes fail). Normal gonadotropic = anatomical/anovulatory (PCOS, Asherman)
The Prolactin Cascade — Why It Causes Infertility
Prolactin → inhibits GnRH (at hypothalamus) → decreased FSH and LH → gonads not stimulated → hypogonadotropic hypogonadism. This is why anything that raises prolactin causes amenorrhea and infertility. It is a physiologic mechanism (lactation) repurposed as pathology when triggered by drugs or tumors.
TRH → Prolactin Connection (Hypothyroidism)
Hypothyroidism → low T3/T4 → no negative feedback → TRH rises → TRH is a potent prolactin stimulator → prolactin rises → GnRH suppressed → infertility. Also: lower T3 → fewer cardiac beta-1 receptors → low heart rate. This chain explains the bradycardia + amenorrhea + weight gain triad of hypothyroidism.
Tuberoinfundibular Dopamine Pathway
Dopamine from the hypothalamus inhibits prolactin secretion via the tuberoinfundibular pathway. Block dopamine (D2 receptor) → prolactin rises. This is why antipsychotics (D2 blockers), metoclopramide, and bromocriptine (dopamine agonist used to treat prolactinomas) all have predictable effects on prolactin.
Treatment of Prolactinomas
| Tumor Size | First-Line Treatment | Drug Mechanism |
|---|---|---|
| Microprolactinoma (<1 cm) | Dopamine agonist (cabergoline > bromocriptine) | D2 agonism → prolactin suppression + tumor shrinkage |
| Macroprolactinoma (>1 cm) with vision loss | Dopamine agonist first; surgery if refractory | Same mechanism; surgery for optic chiasm compression |
Reproductive Genetics & Intersex Conditions
The classic Step 2 trap — AIS vs Müllerian agenesis. RR-100 (EP476) delivers the definitive two-feature framework: genotype (XY vs XX) and Tanner staging of pubic/axillary hair. Know these two differences cold and you will never miss this question on an exam.
RR 100EP476
Androgen Insensitivity vs Müllerian Agenesis
- Androgen insensitivity syndrome (AIS / testicular feminization): 46XY genotype. Testosterone receptor non-functional → no virilization despite male genotype. Phenotypically female. Testes produce AMH (nukes Müllerian duct → no uterus, fallopian tubes, upper vagina) but testosterone doesn't act → no Wolffian structures either
- AIS Tanner staging: Breasts = Tanner 4–5 (estrogen works fine from testes). Pubic/axillary hair = Tanner 1–2 (androgen receptor broken → no pubic/axillary hair). This combination is pathognomonic
- Müllerian agenesis (MRKH syndrome): 46XX genotype. Ovaries intact (ovaries are not Müllerian-derived). Phenotypically female. Müllerian duct fails to develop → no uterus, fallopian tubes, upper vagina. But ovaries produce estrogen AND androgens normally
- MRKH Tanner staging: Breasts = Tanner 4–5 (estrogen normal). Pubic/axillary hair = Tanner 4–5 (androgens from ovary normal). Both sexualization markers fully developed — distinguishes from AIS
- Why both have primary amenorrhea: AIS = testes make AMH → no uterus → no menses. MRKH = Müllerian duct fails → no uterus → no menses. Both lack a uterus but for completely different reasons
- Gonad type: AIS = testes (in inguinal canal or labia — increased malignancy risk → prophylactic orchiectomy after puberty). MRKH = ovaries (normal, no increased cancer risk)
AIS vs Müllerian Agenesis — The Two-Feature Framework
| Feature | AIS (Testicular Feminization) | Müllerian Agenesis (MRKH) |
|---|---|---|
| Genotype | 46XY | 46XX |
| Phenotype | Female | Female |
| Gonad type | Testes (in inguinal canal or labia) | Ovaries (normal position) |
| Uterus / fallopian tubes | Absent (AMH from testes destroys Müllerian duct) | Absent (duct fails to develop) |
| Breast development | Normal / advanced (Tanner 4–5) | Normal / advanced (Tanner 4–5) |
| Pubic / axillary hair | Tanner 1–2 (androgen receptor defect) | Tanner 4–5 (androgen receptor intact) |
| Testosterone level | Normal or elevated (can't respond to it) | Normal female range |
| Cancer risk of gonad | Elevated (testicular gonadoblastoma) — remove after puberty | None |
The Classic Trap on the USMLE
Both AIS and MRKH present with: (1) primary amenorrhea, (2) female external appearance, (3) absent uterus, (4) good breast development. The ONLY reliable differentiator is pubic/axillary hair Tanner staging and genotype. If the question says "no pubic hair" or "sparse pubic hair" — AIS. If pubic hair is normal — MRKH.
Why AIS Has No Wolffian Structures Either
In normal male development, testosterone drives Wolffian duct development. In AIS, testosterone receptor is broken → testosterone cannot act → Wolffian duct also regresses. The person is 46XY but has neither Müllerian derivatives (destroyed by AMH) nor Wolffian derivatives (can't respond to testosterone). Result: phenotypic female with a blind-ending vaginal pouch and no internal reproductive organs.
EP357
Congenital Adrenal Hyperplasia & Ambiguous Genitalia
- 21-hydroxylase deficiency (most common CAH): Blocks cortisol + aldosterone. Shunts steroid precursors to androgens. XX female → virilized external genitalia (clitoromegaly, labial fusion, ambiguous genitalia) but internal structures (uterus, ovaries) intact because ovaries not affected
- Salt-wasting crisis (severe 21-OH deficiency): No aldosterone → hyponatremia + hyperkalemia + hypotension. Presents in first weeks of life as dehydration + shock. Treat with hydrocortisone + fludrocortisone (mineralocorticoid replacement)
- 11β-hydroxylase deficiency: Blocks cortisol only. 11-deoxycorticosterone accumulates (potent mineralocorticoid) → hypertension (not salt-wasting). Still virilized. Key differentiator: CAH + hypertension = 11β-OH deficiency
- True precocious puberty: GnRH-dependent (central): early activation of HPG axis. Breast/pubic hair + accelerated growth + advanced bone age. Treat with GnRH agonist (paradoxically suppresses pulsatile GnRH → suppresses FSH/LH)
- Pseudoprecocious puberty: GnRH-independent (peripheral): steroids produced outside HPG axis control (CAH, McCune-Albright, exogenous steroids). Treat underlying cause. GnRH agonist will NOT work here
- 17α-hydroxylase deficiency: No sex steroids (no androgen, no estrogen) + no cortisol but aldosterone excess → hypertension + hypokalemia. XY individual: phenotypically female (no DHT, no testosterone action). XX individual: primary amenorrhea with no secondary sex characteristics
CAH Enzyme Deficiency Comparison
| Enzyme Deficient | Cortisol | Aldosterone | Sex Steroids | Electrolyte Effect | Classic Presentation |
|---|---|---|---|---|---|
| 21-hydroxylase (most common) | ↓ | ↓ | ↑ androgens | Hyponatremia, hyperkalemia (salt-wasting) | Virilized XX female; salt-wasting crisis neonate |
| 11β-hydroxylase | ↓ | ↓ (but 11-DOC ↑) | ↑ androgens | Hypertension, hypokalemia (11-DOC mineralocorticoid) | Virilized female + hypertension |
| 17α-hydroxylase | ↓ | ↑ (aldosterone excess) | ↓↓ (no sex steroids) | Hypertension, hypokalemia | No sexual development; XY phenotypically female; XX no puberty |
Steroidogenesis Mnemonic
Cholesterol → Pregnenolone → Progesterone → 17-OH-Progesterone → Androstenedione → Testosterone → DHT (and estrogen via aromatase). 21-OH converts progesterone → 11-deoxycorticosterone (toward aldosterone path) AND 17-OH-progesterone → 11-deoxycortisol (toward cortisol path). Block it → cortisol and aldosterone both fail, all precursors pile up and divert to androgens.