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Hair Follicle Growth and Differentiation

Hirsutism, or excessive male-pattern hair growth, affects approximately 10% of women. It is most often caused by idiopathic or polycystic ovary syndrome (PCOS), which results in androgen excess. Less frequently, hirsutism can be caused by adrenal androgen overproduction or serious underlying conditions. Virilization refers to high androgen levels causing signs like deepening of the voice or increased muscle bulk. Virilization may be due to benign ovarian conditions or neoplasms.

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85 views1 page

Hair Follicle Growth and Differentiation

Hirsutism, or excessive male-pattern hair growth, affects approximately 10% of women. It is most often caused by idiopathic or polycystic ovary syndrome (PCOS), which results in androgen excess. Less frequently, hirsutism can be caused by adrenal androgen overproduction or serious underlying conditions. Virilization refers to high androgen levels causing signs like deepening of the voice or increased muscle bulk. Virilization may be due to benign ovarian conditions or neoplasms.

Uploaded by

Camelia M Cami
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© © All Rights Reserved
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Hirsutism

Hirsutism, which is defined as androgen-dependent excessive male-pattern hair growth,


affects ~10% of women. Hirsutism is most often idiopathic or the consequence of
androgen excess associated with polycystic ovary syndrome (PCOS). Less frequently, it
may result from adrenal androgen overproduction as occurs in nonclassic congenital
adrenal hyperplasia (CAH) (Table 387-1). Rarely, it is a harbinger of a serious
underlying condition. Cutaneous manifestations commonly associated with hirsutism
include acne and male-pattern balding (androgenic alopecia). Virilization refers to a
condition in which androgen levels are sufficiently high to cause additional signs and
symptoms, such as deepening of the voice, breast atrophy, increased muscle bulk,
clitoromegaly, and increased libido. Virilization may be due to benign hyperplasia of
ovarian theca and stroma cells (e.g., hyperthecosis); it may also result from an ovarian
or adrenal neoplasm.

TABLE 387-1Causes of Hirsutism


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HAIR FOLLICLE GROWTH AND DIFFERENTIATION
Hair can be categorized as either vellus (fine, soft, and not pigmented) or terminal (long,
coarse, and pigmented). The number of hair follicles does not change over an
individual’s lifetime, but the follicle size and type of hair can change in response to
numerous factors, particularly androgens. Androgens are necessary for terminal hair
and sebaceous gland development and mediate differentiation of pilosebaceous units
(PSUs) into either a terminal hair follicle or a sebaceous gland. In the former case,
androgens transform the vellus hair into a terminal hair; in the latter case, the
sebaceous component proliferates and the hair remains vellus.

There are three phases in the cycle of hair growth: (1) anagen (growth phase),
(2) catagen (involution phase), and (3) telogen (rest phase). Depending on the body
site, hormonal regulation may play an important role in the hair growth cycle. For
example, the eyebrows, eyelashes, and vellus hairs are androgen-insensitive, whereas
the axillary and pubic areas are sensitive to low levels of androgens. Hair growth on the
face, chest, upper abdomen, and back requires higher levels of androgens and is
therefore more characteristic of the pattern typically seen in men. Androgen excess in
women can lead to increased hair growth in most androgen-sensitive sites except in the
scalp region, where hair loss occurs because androgens cause scalp hairs to spend
less time in the anagen phase.

Although androgen excess underlies most cases of hirsutism, there is only a modest
correlation between androgen levels ...

C2 General

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