Androgenic Alopecia

Androgenic alopecia (AGA), also known as common baldness or male- or female-pattern baldness, is an extremely common, noninflammatory type of alopecia that results from the action of androgens on the hair follicle.
AGA is an inherited physical trait whose incidence increases greatly with advancing age.
In most, if not all, cultures, hair plays a powerful role in a person's psychosexual identity and self-image. It is not surprising that in our youth- and image-driven society, hair replacement and retention methods have taken on almost the status of a subspecialty in health care.
AGA is seen more frequently in men than in women because women's hair loss tends to be less apparent, less extensive, and generally begins at a later age than in men.
The condition is genetically determined (autosomal dominant with variable penetrance). The incidence and severity of AGA tends to be highest in white men, followed by white women; it is second highest in Asians and African-Americans and lowest in Native Americans and Eskimos.

Pathogenesis ⬆ ⬇

AGA results from the action of dihydrotestosterone (DHT) on the hair follicle that results in a shortened anagen phase of the hair cycle, thus producing thinner, shorter hairs with each cycle.
Gradually, terminal hairs are converted into indeterminate hairs and finally into short, wispy, nonpigmented vellus hairs in a process known as miniaturization.
In women, estrogen may protect against androgen-mediated miniaturization, which explains the more gradual onset, less severe disease course and the increased incidence after menopause.

Clinical Manifestations ⬆ ⬇

Androgenic alopecia produces two typical patterns of hair loss:

In men, AGA usually begins in late adolescence or young adulthood, with hair loss often starting at the parietal hairline.
Hair loss may progress to an M-shaped pattern on the front and later involve the vertex of the scalp (male-pattern baldness; Fig. 19.1).
In women, the loss of hair is more subtle and tends to begin at an older age. AGA in women, also termed female-pattern hair loss (FPHL), is typically characterized by a thinning of the hair at the crown of the scalp in a “Christmas-tree,” midparietal pattern with preservation of the frontal hairline (Figs. 19.2 and 19.3).
Hair loss may progress in both sexes but is more extensive in men.
In end-stage AGA, many men have only a fringe of remaining hair usually at the occipital scalp, whereas women tend to maintain the frontal hairline and do not become frankly bald.
Hair density on the occipital scalp remains unaffected.

Diagnosis ⬆

The diagnosis of AGA is generally based on the clinical pattern of baldness coupled with an absence of clues pointing to a specific disease that may cause hair loss.

Differential Diagnosis

Management

Women

Minoxidil 2% or 5% solution (Rogaine), applied twice daily, may reduce shedding and possibly contribute to some regrowth.
A 5% solution of minoxidil in a foam formula (Women's Rogaine) is applied once daily.
Regrowth is more pronounced at the vertex than in the frontal areas and may not be noted for at least 4 months.
The mechanism of action is unknown; however, minoxidil appears to lengthen the duration of the anagen phase, and it may increase the blood supply to the hair follicle.
Continued use is necessary indefinitely because discontinuation of treatment produces a rapid reversion to the pretreatment balding pattern.
Women with a recent onset of AGA and small areas of hair loss respond best to minoxidil.
Women with excess androgen may benefit from systemic antiandrogen therapy with agents such as spironolactone, flutamide, or oral contraceptives that decrease ovarian and adrenal androgen production, especially agents that contain a nonandrogenic progestin.

Men

Minoxidil 5% solution (Rogaine), applied twice daily, may reduce shedding and contribute to some regrowth.
Finasteride (Propecia), 1 mg/day, is an oral antiandrogen that acts by inhibiting type II 5-alpha reductase, the enzyme that converts testosterone to dihydrotestosterone. It is very effective in reducing further hair loss and increasing hair density.
Recognized side effects include erectile dysfunction and, less often, gynecomastia.
Finasteride is teratogenic and has not been approved for the treatment of AGA in women.

Men and Women

HairMax LaserComb is a medical laser device for home use that has been FDA cleared for the treatment of AGA in men and women. Several studies have shown increase in hair thickness and density with regular use.
Hair transplantation is performed by harvesting intact healthy hair follicles from donor sites, usually the occipital scalp, and inserting them into the areas of hair loss.
Hair transplantation using a micrografting technique in which a small incision is used to insert one or more donor hairs, is particularly effective in women, because unlike men, women rarely become completely bald.

Helpful Hints

Blood tests and other laboratory studies are necessary only when the diagnosis is in doubt, or if investigation into other causes of alopecia is warranted by the history or physical examination (see later section, “Diffuse Alopecia”).
Women with symptoms or signs of virilization should undergo a careful evaluation including hormone studies for an androgen-excess syndrome. These patients may need referral to an endocrinologist.
Healthcare providers should take a patient's hair loss-related anxiety seriously. Hair loss should not simply be “brushed off” as an insignificant cosmetic complaint. The time spent listening to the patient may be helpful in uncovering other emotional or physical problems.

Point to Remember

AGA is very common; therefore, it may coexist with other forms of hair loss. Consequently, a search for treatable causes (e.g., anemia, hypothyroidism), especially in patients with an abrupt onset or a rapid progression of their disease, is indicated (see discussion below in this chapter).

SEE PATIENT HANDOUT “Hair Loss” IN THE COMPANION eBOOK EDITION.