What are the causes of hirsutism in women?

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Causes of Hirsutism in Women

Polycystic ovary syndrome (PCOS) is the most common cause of hirsutism, accounting for the vast majority of cases, followed by idiopathic hirsutism (increased hair follicle sensitivity to normal androgen levels without detectable hyperandrogenemia). 1

Primary Pathophysiology

Hirsutism results from two key mechanisms working together 1:

  • Elevated circulating androgens (hyperandrogenemia)
  • Increased hair follicle sensitivity to androgens through local conversion of testosterone to dihydrotestosterone by 5α-reductase

Approximately half of women with mild hirsutism have normal androgen levels, indicating that follicular hypersensitivity alone can cause the condition 1.

Common Causes (in order of frequency)

1. Polycystic Ovary Syndrome (PCOS)

  • Accounts for 3 out of 4 cases of hirsutism 2
  • Caused by gonadotropin-dependent functional ovarian hyperandrogenism 1
  • May include mild ACTH-dependent functional adrenal hyperandrogenism
  • Often presents with menstrual irregularity, infertility, acne, central obesity, or acanthosis nigricans 1

2. Idiopathic Hirsutism

  • Constitutes 5-17% of cases depending on ethnicity 3
  • Normal androgen levels with increased follicular sensitivity
  • Diagnosis made by exclusion 4
  • Regular menses and no other endocrine abnormalities

3. Nonclassic Congenital Adrenal Hyperplasia (NCAH)

  • Present in 1-8% of hirsute women 3
  • Most commonly due to 21-hydroxylase deficiency 1
  • Less than 5% of hyperandrogenic women in general population 1

4. Medications

  • Androgenic drugs: anabolic steroids, danazol 1
  • Valproic acid 1
  • Must obtain detailed drug history, especially in athletes 1

Rare but Critical Causes (Require Urgent Identification)

Androgen-Secreting Tumors

  • Present in approximately 0.2% of hyperandrogenic women 1
  • Over half are malignant 1
  • Red flags include:
    • Rapid onset or rapidly progressive hirsutism
    • Virilization signs (clitoromegaly, increased muscularity, deepening voice)
    • Palpable abdominal or pelvic mass 1
    • Total testosterone >200 ng/dL 4, 2

Other Endocrinopathies

These typically present with their primary manifestations first 1:

  • Cushing's syndrome - look for central obesity, striae, moon facies
  • Hyperprolactinemia - galactorrhea, amenorrhea
  • Acromegaly - coarse facial features, enlarged hands/feet
  • Thyroid dysfunction - weight changes, temperature intolerance

Hyperandrogenic-Insulin-Resistant Acanthosis Nigricans (HAIR-AN) Syndrome

  • Approximately 3% of hyperandrogenic women 3
  • Severe insulin resistance with acanthosis nigricans

Important Clinical Caveats

Ethnic considerations: Even mild hirsutism in Asian women may indicate excess androgen production, whereas Mediterranean or Middle Eastern women may have more terminal hair growth as a normal variant 1.

Severity correlation: The degree of hirsutism (Ferriman-Gallwey score) does not correlate well with androgen levels because follicular response to androgens varies considerably 1.

Mild hirsutism with regular menses: Approximately half of isolated mild hirsutism cases (Ferriman-Gallwey score 8-15) are unrelated to hyperandrogenemia, making extensive testing unnecessary in this population 1.

Tumor presentation: Tumors producing only moderately excessive androgens can have indolent presentations, so maintain clinical suspicion even without dramatic virilization 1.

References

2
Research

Hirsutism in women.

American family physician, 2012

4
Research

Hirsutism: diagnosis and treatment.

Arquivos brasileiros de endocrinologia e metabologia, 2014

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