What are idiopathic androgenic alopecia and idiopathic hirsutism?

Androgenetic Alopecia and Idiopathic Hirsutism: Definitions and Clinical Context

Androgenetic Alopecia (AGA)

Androgenetic alopecia is a genetically determined, androgen-mediated condition causing progressive miniaturization of hair follicles, resulting in patterned hair loss that begins between ages 12-40 years in both women and men. 1

Pathophysiology

• Dihydrotestosterone (DHT) binds to androgen receptors in genetically susceptible hair follicles, activating genes that transform large terminal follicles into miniaturized follicles 1
• Women with AGA have higher levels of 5α-reductase and androgen receptors in frontal hair follicles compared to occipital follicles 1
• Critically, women also have much higher levels of cytochrome p-450 aromatase in frontal follicles than men, which provides some protective effect and explains the different pattern of hair loss between sexes 1

Clinical Presentation in Women

• Increased thinning over the frontal/parietal scalp with greater density over the occipital scalp 1
• Retention of the frontal hairline (unlike male pattern baldness) 1
• Presence of miniaturized hairs on examination 1
• Early age of onset (12-40 years) 1

Important Clinical Distinction

• Most women with AGA have normal menses and pregnancies 1
• Extensive hormonal testing is not needed unless signs of androgen excess are present, such as hirsutism, severe unresponsive cystic acne, virilization, or galactorrhea 1
• The American Academy of Dermatology notes that androgenic alopecia is an indicator of hyperandrogenism when accompanied by other signs 2

Cardiovascular Risk Association

• Androgenetic alopecia is associated with increased risk of ischemic heart disease, with greater risk correlating with degree of baldness 3
• Associated comorbidities include hypertension, hyperinsulinemia, metabolic syndrome, and dyslipidemia 3

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Idiopathic Hirsutism

Idiopathic hirsutism is excessive terminal hair growth in a male pattern in women who have normal ovulatory function, normal serum androgen levels, and normal ovarian morphology—though recent evidence suggests this may be a misnomer. 4, 5

Strict Diagnostic Criteria

• Normal ovulatory function must be documented (not just regular menses, as up to 40% of eumenorrheic hirsute women are anovulatory) 4
• Normal circulating androgen levels 4
• Normal ovarian morphology 5
• When strictly defined, idiopathic hirsutism accounts for less than 20% of all hirsute women 4

Pathophysiology: The "Idiopathic" Controversy

• Primary increase in skin 5α-reductase activity (both type 1 and type 2 isoenzymes) 4
• Possible alteration in androgen receptor function 4
• Recent evidence shows "relative hyperandrogenemia"—androgen levels that are higher than healthy controls but still within normal laboratory ranges 5
• Increased expression of steroid sulfatase and 17-beta hydroxysteroid dehydrogenase mRNA in skin, contributing to local androgen metabolism and production 5

Clinical Implications of New Understanding

• The term "idiopathic" may be a misnomer; "normoandrogenic hirsutism" has been proposed as more accurate 5
• May represent an early stage of hyperandrogenic disorders such as PCOS rather than a distinct entity 5
• Often familial, suggesting genetic predisposition 6

Differential Diagnosis Requirements

The American Academy of Dermatology and American Academy of Family Physicians recommend excluding 2:

• Polycystic ovary syndrome (PCOS) - most common cause in young women 2
• Nonclassic congenital adrenal hyperplasia 2
• Cushing's syndrome 2
• Androgen-secreting tumors (ovarian or adrenal) - particularly if testosterone levels very high or rapid symptom onset 2
• Thyroid disease and hyperprolactinemia 2
• Exogenous androgen use (medications or supplements) 2

Treatment Response

• Patients respond to antiandrogen therapy or 5α-reductase inhibitor therapy 4
• Pharmacological suppression of ovarian or adrenal androgen secretion provides limited additional benefit 4
• Mechanical treatments include laser hair removal, electrolysis, depilatory creams, plucking, and waxing 6

Key Clinical Pitfall

Do not diagnose idiopathic hirsutism based solely on regular menses—up to 40% of women with regular periods and hirsutism have ovulatory dysfunction requiring documentation of normal ovulation 4. This is the most common diagnostic error leading to misclassification of PCOS as idiopathic hirsutism.