Causes of Hirsutism
Hirsutism is most commonly caused by polycystic ovary syndrome (PCOS), followed by idiopathic hirsutism, with rarer causes including non-classical congenital adrenal hyperplasia, adrenal or ovarian tumors, Cushing syndrome, and medication effects. 1
Primary Causes
1. Polycystic Ovary Syndrome (PCOS)
- Most common cause (accounts for approximately 70-80% of cases) 1, 2
- Characterized by:
- Hyperandrogenic chronic anovulation
- Elevated LH/FSH ratio >2
- Insulin resistance and hyperinsulinemia
- Polycystic ovaries on ultrasound (>10 peripheral cysts)
- Affects 4-6% of general female population 3
2. Idiopathic Hirsutism
- Second most common cause (5-17% of cases depending on ethnicity and geography) 4
- Diagnosis of exclusion when no identifiable hormonal abnormality is found
- Normal ovulatory cycles and normal androgen levels
- May be due to increased sensitivity of hair follicles to normal androgen levels
3. Non-Classical Congenital Adrenal Hyperplasia (NCAH)
- Accounts for 1-8% of hirsutism cases 4
- Most commonly due to 21-hydroxylase deficiency
- Characterized by:
- Elevated 17-hydroxyprogesterone levels
- Modest elevation of testosterone
- May have elevated DHEAS levels 1
4. Androgen-Secreting Tumors
- Rare but serious cause (adrenal or ovarian tumors)
- Red flags include:
5. Cushing Syndrome
- Rare cause of hirsutism
- Associated with:
- Cortisol excess
- Central obesity, purple striae, buffalo hump
- Hypertension, hyperglycemia, hypokalemia 3
- Proximal muscle weakness
Other Causes
6. Hyperandrogenic-Insulin Resistant Acanthosis Nigricans Syndrome
- Approximately 3% of hyperandrogenic women 4
- Characterized by insulin resistance and dark, velvety skin patches
7. Hyperprolactinemia
- Can cause hirsutism through indirect effects on androgen metabolism
- May be associated with pituitary adenomas 3
8. Medications
- Androgens and anabolic steroids
- Certain progestins
- Danazol
- Phenytoin
- Cyclosporine
- Minoxidil 1
9. Thyroid Disorders
- Both hypothyroidism and hyperthyroidism can affect hair growth patterns 2
10. Acromegaly
- Excess growth hormone can lead to hirsutism 4
- Often associated with coarse facial features and enlarged hands/feet
Diagnostic Approach
Laboratory Evaluation
Initial testing:
- Testosterone (total and free)
- DHEAS (dehydroepiandrosterone sulfate)
- 17-hydroxyprogesterone (to evaluate for NCAH)
- LH/FSH ratio (>2 suggests PCOS) 1
Additional testing based on clinical suspicion:
- Morning cortisol and ACTH (if Cushing syndrome suspected)
- Prolactin levels
- Thyroid function tests
- Fasting glucose and insulin (for insulin resistance) 1
Imaging
- Pelvic ultrasound if PCOS suspected
- Adrenal CT/MRI if adrenal tumor suspected (particularly with DHEAS >3800 ng/ml in women 20-29 years or >2700 ng/ml in women 30-39 years) 3, 1
Clinical Pearls
- Serum testosterone >200 ng/dL should prompt immediate evaluation for an androgen-secreting tumor 5
- Androgen-secreting tumors can be life-threatening and require prompt diagnosis and treatment 4
- In women with epilepsy, PCOS prevalence is higher (10-25%) than in the general population (4-6%) 3
- Hirsutism reflects the interaction between circulating androgen concentrations, local androgen concentrations, and the sensitivity of hair follicles to androgens 5
- Treatment should be continued for at least 6 months before assessing efficacy due to the length of the hair growth cycle 2
By systematically evaluating patients with hirsutism using this approach, clinicians can identify the underlying cause and implement appropriate treatment strategies to address both the cosmetic concerns and any associated health risks.