Androgenetic alopecia (male-pattern baldness)
Although clearly familial, the exact mode of inherit-ance has not yet been clarified. The idea of a single autosomal dominant gene, with reduced penetrance in women, now seems less likely than a polygenic type of inheritance. Male-pattern baldness is androgen-dependent; in females, androgenetic alopecia, with circulating levels of androgen within normal limits, is seen only in those who are strongly predisposed genetically.
The common pattern in men (Fig. 13.9) is the loss of hair first from the temples, and then from the crown.
However, in women the hair loss may be much more diffuse (Fig. 13.10), particularly over the crown. In bald areas, terminal hairs are replaced by finer vellus ones.
Hair loss is relentless, tending to follow the family pattern with some losing hair quickly and others more slowly. The diffuse pattern seen in women tends to progress slowly.
Even minor hair loss may lead to great anxiety and rarely to a monosymptomatic hypochondriasis. Bald scalps burn easily in the sun, and may develop multiple actinic keratoses. It has been suggested recently that bald men are more likely to have a heart attack than those with a full head of hair.
The diagnosis is usually obvious in men, but other causes of diffuse hair loss have to be considered in women.
None are usually needed. In women virilization may have to be excluded.
Scalp surgery, hair transplants and wigs are welcomed by some. Topical application of minoxidil lotion may slow early hair loss and even stimulate new growth of hair in a few cases. Small and recently acquired patches respond best. When minoxidil treatment stops, the new hairs fall out after about 3 months. Anti-androgens help some women with the diffuse type of androgenetic alopecia.
Finasteride (Propecia), an inhibitor of human type
II 5α-reductase, reduces serum and scalp skin levels of dihydrotestosterone in balding men. At the dosage of 1 mg /day, it may increase hair counts and so lead to a noticeable improvement in scalp hair. However, the beneficial effects slowly reverse once treatment has stopped. This treatment is not indicated in women or children. Side-effects are rare, but include decreased libido, erectile dysfunction and altered prostate-specific antigen levels.