TREATMENT OF HAIR LOSS FOR MEN

TREATMENT OF HAIR LOSS

HAIR loss is a common and distressing symptom. With the approval of two drugs that promote hair growth finasteride and minoxidil Ñ we can now treat patients with some types of hair loss. Both drugs influence the hair-growth cycle and increase the length and diameter of existing hair, although their mechanisms of action differ. In this article, I will focus on the treatment of two common problems, androgenetic alopecia and alopecia areata, both of which involve a reversible alteration of the hair-growth cycle.

THE HAIR-GROWTH CYCLE

Hair growth is cyclic, with phases of growth (anagen), involution (catagen), and rest (telogen) . The cycles of active growth and rest are regulated by complex messages between the epithelium and the dermis that are not yet well understood. In a normal scalp, most follicles are growing (90 to 95 percent), a few are undergoing involution (less than 1 percent), and the remainder are resting (5 to 10 percent). At the end of telogen, hair is released and shed and the next cycle is initiated. Each day, up to 100 hairs in telogen are shed from the head and about the same number of follicles enter anagen. The duration of anagen determines the length of hair, and
the volume of the hair bulb determines the diameter. We are born with all our terminal hair follicles Ñ
approximately 100,000 on the scalp Ñ that are predetermined to grow long, thick hair. Other follicles are predetermined to grow vellus hair, which is short, fine, and relatively nonpigmented and covers much of the body. Follicles can become larger or smaller under systemic and local influences that alter the duration of anagen and the volume of the hair matrix.

ANDROGENETIC ALOPECIA

Androgenetic alopecia is hereditary thinning of the hair induced by androgens in genetically susceptiblemen and women. 7,8 This condition is also known as male-pattern hair loss or common baldness in men and as female-pattern hair loss in women. Thinning of the hair usually begins between the ages of 12 and 40 years in both sexes, and approximately half the population expresses this trait to some degree before the age of 50. 9,10 The pattern of inheritance is polygenic. 11,12

Pathophysiology

In susceptible hair follicles of the scalp, dihydrotestosterone binds to the androgen receptor, and the
hormone-receptor complex then activates the genes responsible for the gradual transformation of large,
terminal follicles to miniaturized follicles. 13-16 With successive hair cycles, the duration of anagen shortens
and the follicles become smaller, producing shorter, finer hairs that cover the scalp poorly. These miniaturized
hairs of various lengths and diameters are the hallmark of androgenetic alopecia. 8,10,17 At the same time, the number of follicles per unit of area remains the same.Dihydrotestosterone is formed by the periphera conversion of testosterone by 5 a-reductase. There are two isoforms of 5-reductase Ñ type 1 and type 2 Ñwhich, together with other enzymes, regulate specific steroid transformations in the skin.

Treatment in Men

In men, androgenetic alopecia ranges from the bitemporal recession of hair, to thinning of the frontal and vertex regions of the scalp, to complete baldness and loss of all hair except the occipital and temporal fringes. In some cases, men have diffuse thinning.


Cycle of Scalp-Hair Growth

Figure 1.

Every scalp hair has a phase of growth (anagen), which lasts two to six years; a phase of involution (catagen), which lasts two to three weeks; and a resting phase (telogen), which lasts two to three months and is followed by shedding of the hair. The cycle is then repeated. All hair loss affects or disrupts one of these phases.

Figure 2.

Change in the Mean (±SE) Hair Count from Base Line (Month 0) at the Anterior Leading Edge of the Vertex Thinning Area in Men Given 1 mg of Finasteride or Placebo Daily for 24 Months. In the second year, some men who received placebo during the first 12 months were given finasteride and some who initially received finasteride were given placebo. The dotted line indicates no change. Adapted from Kaufman et al. 29 with the permission of the publisher.


Figure 3.

Mean Percent Change in Hair Weight per Square Centimeter of Scalp from Base Line (Week 0) among Men with Androgenetic Alopecia Who Received 5 Percent Minoxidil, 2 Percent Minoxidil, Placebo, or No Treatment for 96 Weeks. The dotted line indicates no change, and the vertical arrow at 96 weeks marks the cessation of treatment. Adapted from Price et al. 45 with the permission of the publisher.