What is PCOS and how common is it?
Polycystic ovary syndrome (PCOS) is the most common endocrine disorder of women of reproductive age, affecting roughly 5% to 26% depending on the diagnostic criteria used. It was first described by Stein and Leventhal in 1935. It is a diagnosis of exclusion built on three features — chronic anovulation, hyperandrogenism and polycystic ovaries — and it is now recognised as much a metabolic disease as a reproductive one.
Current StatPearls text notes that an international consensus has recently renamed PCOS as polyendocrine metabolic ovarian syndrome (PMOS). Exams and most textbooks still use PCOS, so use that name in answers, but expect to see PMOS in recent literature.
What is the pathophysiology of PCOS?
PCOS involves a self-reinforcing loop between insulin resistance, ovarian androgen excess and altered gonadotropin secretion. Key links:
- Insulin resistance and hyperinsulinaemia — present in about 70% of women with PCOS and independent of adiposity. Insulin sensitises the ovary to LH and, in the liver, lowers sex hormone-binding globulin (SHBG), so more testosterone is free.
- Theca cells over-express steroidogenic enzymes (including P450c17), producing excess androgens.
- LH relatively high versus FSH — altered pulsatile GnRH raises LH; the relatively low FSH fails to drive granulosa aromatase, so androgens are not converted efficiently to estradiol.
- Impaired follicle selection — androgens speed recruitment of primordial follicles but cause premature luteinisation and block dominant follicle selection, giving many small follicles and anovulation (polycystic ovarian morphology).
- Peripheral aromatisation — excess androgens convert to oestrone in adipose tissue; chronic unopposed oestrogen can cause endometrial hyperplasia.
- AMH is raised in PCOS and reflects the large number of small follicles.
What are the diagnostic criteria for PCOS?
Most societies accept a diagnosis when at least 2 of 3 criteria are present after excluding other causes. These are the Rotterdam (ESHRE/ASRM 2003) criteria, the most commonly used. The older NIH 1990 criteria required clinical or biochemical hyperandrogenism and oligo- or anovulation.
| Criterion | What counts |
|---|---|
| 1. Oligo- or anovulation | Irregular cycles (2023 guideline definitions): for example intervals <21 or >35 days, or <8 cycles a year from 3 years after menarche; any cycle >90 days; primary amenorrhoea by 15 years |
| 2. Hyperandrogenism | Clinical (hirsutism, acne, alopecia) or biochemical (raised total or free testosterone) |
| 3. Polycystic ovaries | Classic ultrasound definition: ≥12 follicles of 2–9 mm in an ovary and/or ovarian volume ≥10 cm³ (one ovary is enough). Current 2023 international guideline: ≥20 follicles per ovary in adults, or raised AMH |
- Adults with irregular cycles plus hyperandrogenism do not need ultrasound or AMH to diagnose PCOS.
- Adolescents: both hyperandrogenism and ovulatory dysfunction must be present; ultrasound and AMH are not recommended because of low specificity.
- Normal-looking cycles do not exclude anovulation — check mid-luteal progesterone if confirmation is needed.
- Phenotypes A to G are described; phenotype A (classic) has all four of hyperandrogenism, hirsutism, oligo-anovulation and polycystic ovaries and is the commonest.
What is hirsutism and how is the Ferriman-Gallwey score used?
Hirsutism is excessive coarse, dark terminal hair in a male pattern in a woman — on the upper lip and chin, chest, areolae, linea alba, sacrum, buttocks and inner thighs. It reflects the interaction between circulating androgen levels and the sensitivity of the hair follicle: testosterone is converted in the skin by 5α-reductase into the more potent dihydrotestosterone (DHT). It is most often due to hyperandrogenism, and PCOS causes about 75% of cases.
Severity is graded with the Ferriman-Gallwey (FG) score. In the original description, nine body areas are each scored by hair density from none to severe; a total above 7 is abnormal (maximum 36). The modified FG (mFG) score used in the 2023 PCOS guideline sets the diagnostic threshold between 4 and 6, depending on ethnicity.
| Cause | Key points |
|---|---|
| PCOS | About 75% of cases. Starts at puberty with menstrual disturbance, weight gain, acne, acanthosis nigricans and insulin resistance |
| Non-classical CAH | Partial 21-hydroxylase deficiency, an autosomal recessive condition; the commonest adrenal cause of hyperandrogenism. Mimics PCOS |
| Idiopathic hirsutism | Regular menses, normal ovaries, normal androgens; diagnosis of exclusion. Follicle hypersensitivity to androgens with raised 5α-reductase activity; about 10% of all cases and ~50% of mild cases |
| Androgen-secreting tumour | Rare (about 0.2% of cases); autonomous, rapid onset with virilisation and a pelvic or abdominal mass; about half are malignant |
| Drugs | Androgens, glucocorticoids, progestins, clomiphene, tamoxifen, minoxidil, ciclosporin, danazol, diazoxide, phenytoin, D-penicillamine, interferon |
| Endocrinopathies | Cushing syndrome (ACTH), hyperprolactinaemia, acromegaly, thyroid disease: all rare as isolated causes |
How is a woman with hirsutism or suspected PCOS investigated?
The aim is to confirm hyperandrogenism, exclude mimics and screen for metabolic disease. The baseline hormone panel is taken in the early follicular phase (days 3–6 of the cycle, early morning, fasting), after stopping any oral contraception for two or three cycles unless a tumour is suspected.
- Total and free testosterone (free androgen index); measure by liquid chromatography or mass spectrometry where possible — direct immunoassays are less accurate. If these are not raised, androstenedione and DHEAS may be measured.
- 17-hydroxyprogesterone for non-classical CAH, then an ACTH stimulation test if needed.
- TSH and prolactin when cycles are irregular.
- LH/FSH, SHBG, and a dexamethasone suppression test if Cushing syndrome is suspected.
- Very high androgen levels or virilisation — look for an ovarian or adrenal tumour or other causes of hyperandrogenaemia.
- Metabolic screen: BMI and waist circumference, blood pressure, lipids, and a 75 g oral glucose tolerance test (preferred over HbA1c, which is less sensitive in PCOS), repeated every 3–4 years.
How are PCOS and hirsutism treated?
Lifestyle modification is the primary treatment for every woman with PCOS. A modest weight loss of about 5% can bring back ovulation and improve fertility. Drug therapy is then tailored to the complaint.
| Problem | First-line choice | Notes |
|---|---|---|
| Cycle irregularity, hirsutism, acne | Combined hormonal contraceptive (pill, patch or ring) | Progestin lowers LH and ovarian androgens; oestrogen raises SHBG. Choose a low-dose (20 µg ethinyl oestradiol) pill with an antiandrogenic or neutral progestin |
| Hirsutism not controlled after ~6 months of OCP or cosmetic treatment | Add an antiandrogen — spironolactone | Effect is slow (months). Antiandrogens are teratogenic, so reliable contraception is required. Finasteride, flutamide, cyproterone are riskier choices |
| Facial hirsutism, cosmetic | Topical eflornithine, laser photoepilation, electrolysis | Drugs take months to a year or two to work, so cosmetic measures bridge the gap |
| Infertility (anovulatory) | Letrozole first-line | Clomiphene plus metformin is better than clomiphene alone if letrozole is not used |
| Metabolic (insulin resistance), OCP contraindicated | Metformin | Useful for menstrual irregularity; metformin plus OCP beats either alone for hirsutism |
| Obesity | Lifestyle; consider GLP-1 agonists | GLP-1 agonists lower BMI and testosterone but are not yet approved for PCOS as an indication |
What are the long-term complications of PCOS?
- Infertility — anovulation; even women with regular cycles can be anovulatory.
- Endometrial hyperplasia and cancer — unopposed oestrogen; counsel to report abnormal bleeding (routine ultrasound screening is not recommended in asymptomatic women).
- Type 2 diabetes and impaired glucose tolerance; metabolic syndrome; dyslipidaemia; hypertension.
- Obstructive sleep apnoea.
- MASLD (fatty liver) — about three times the risk.
- Depression and anxiety, with higher rates of depression and suicide attempts.
- Pregnancy complications — excess weight worsens miscarriage and live-birth outcomes after fertility treatment.
With age, hirsutism and acne diminish and ovulation improves, but the metabolic risks persist, so long-term screening continues. See also amenorrhoea, abnormal uterine bleeding (PALM-COEIN) and anti-diabetic drugs.
What are the common exam traps in PCOS and hirsutism?
- Rotterdam = 2 of 3; NIH 1990 = hyperandrogenism and oligo-anovulation (no ultrasound).
- Ultrasound in the classic criterion: ≥12 follicles (2–9 mm) and/or volume ≥10 cm³; adolescents are diagnosed without ultrasound.
- Hirsutism score: FG >7 in the original scale; mFG threshold 4–6 in the 2023 guideline.
- First-line for menstrual irregularity or hirsutism: combined OCP; for infertility: letrozole.
- Rapid-onset hirsutism with virilisation → tumour, not PCOS.
- Normal BMI does not exclude PCOS; normal cycles do not exclude anovulation.
- LH is relatively raised against FSH, but this is not one of the diagnostic criteria.
- Spironolactone, finasteride, flutamide: all need contraception — teratogenic.