What are the causes of hirsutism?

Causes of Hirsutism

Polycystic ovary syndrome (PCOS) is the most common cause of hirsutism, accounting for 70-80% of cases, followed by idiopathic hirsutism (5-17%), and non-classical congenital adrenal hyperplasia (1-8%). 1, 2

Primary Endocrine Causes

PCOS (Most Common)

• PCOS affects approximately 4-6% of women and causes 70-80% of all hirsutism cases through hyperandrogenic chronic anovulation, accelerated pulsatile GnRH secretion, insulin resistance, and hyperinsulinemia 1
• The pathophysiology involves hypersecretion of luteinizing hormone leading to ovarian theca stromal cell hyperactivity and increased androgen production 3
• Clinical features include oligomenorrhea/amenorrhea, acne, androgenic alopecia, obesity, and acanthosis nigricans 1, 3

Idiopathic Hirsutism

• Constitutes 5-17% of hirsutism cases depending on ethnicity and geographic area 2
• Diagnosed by exclusion when androgen levels are normal or mildly elevated without identifiable cause 4, 5
• Represents 5-10% of affected women in most populations 6

Non-Classical Congenital Adrenal Hyperplasia (21-Hydroxylase Deficiency)

• Accounts for 1-8% of women with hirsutism, with prevalence varying by ethnicity 2
• Can represent 1-10% of cases depending on ethnic background 6
• Should be screened for with 17-hydroxyprogesterone levels 1

Androgen-Secreting Tumors (Life-Threatening)

Total testosterone or free testosterone levels >200 ng/dL strongly suggest an androgen-secreting tumor requiring urgent evaluation 1

Ovarian Tumors

• Tend to secrete a narrower range of androgens and may present more occultly than adrenal tumors 7
• Pelvic examination should assess for adnexal masses 1

Adrenal Tumors

• Produce excessive amounts of a wide variety of C19 androgens 7
• DHEAS measurement helps identify adrenal androgen production 3

Other Endocrine Disorders

Cushing's Syndrome

• Rare cause of hirsutism presenting with weight gain, proximal muscle weakness, hypertension, psychiatric disturbances, centripetal obesity, purple striae, buffalo hump, hyperglycemia, and hypokalemia 8, 2

Hyperprolactinemia

• Can cause menstrual irregularity and hirsutism 3, 2
• Requires prolactin measurement for exclusion 1, 3

Acromegaly

• Rare cause of hirsutism associated with growth hormone excess 2

Thyroid Disease

• Should be excluded with TSH measurement 3

Insulin Resistance Syndromes

HAIR-AN Syndrome

• Hyperandrogenic-insulin-resistant acanthosis nigricans syndrome affects approximately 3% of hyperandrogenic women 2
• Characterized by severe insulin resistance with dark, velvety skin patches 3

Medication-Induced Hirsutism

Exogenous Androgens

• Direct androgen supplementation or anabolic steroids 1, 3

Antiepileptic Drugs

• Enzyme-inducing drugs (carbamazepine, phenobarbital, phenytoin) alter sex hormone metabolism and increase SHBG production 3
• Women with epilepsy have higher PCOS prevalence (10-25%) even without antiepileptic drugs 1

Androgenic Progestins

• Norethisterone derivatives and levonorgestrel can worsen hirsutism 1

Rare Causes

Glucocorticoid Resistance Syndrome

• Uncommon cause requiring specialized evaluation 2

Ovarian Hyperthecosis

• Represents severe end of the androgenized ovary spectrum with marked ovarian histologic abnormalities 7

Chronic Skin Irritation

• Can stimulate local hair growth 6

Key Diagnostic Considerations

The most important purpose of investigation is identifying androgen-secreting tumors due to their life-threatening potential 2

• Rapid onset of symptoms or virilization (clitoromegaly, voice deepening) suggests tumor 1, 3
• Testosterone >200 ng/dL warrants imaging for tumor exclusion 1, 4
• Mild hirsutism without oligomenorrhea, infertility, clitoromegaly, or truncal obesity may not require extensive endocrine testing 1