Androgenic alopecia, also known as male pattern baldness or female pattern hair loss, is a major form of hair loss. The age at onset is variable and likely has a genetic determination. Some men lose their entire scalp hair, resulting in baldness. Baldness is rare in women, because their hair loss manifests as varying grades of thinning.
Clinical Findings: There are variable degrees of male pattern hair loss. The Hamilton-Norwood scale has been used to grade the degree of hair loss. Grade I is manifested by receding frontal hair. Grade VII is near-total loss of the scalp hair with some sparing of the inferior occiput. The age at onset of androgenic alopecia in men can be any time from puberty into adulthood. Most men older than 50 years of age exhibit some form of androgenic hair loss. The Caucasian population is much more prone to developing androgenic alopecia than the African American or Asian population.
|HAMILTON-NORWOOD SCALE FOR MALE PATTERN BALDNESS|
Female pattern hair loss can be more difficult to treat because of the importance society places on appearance and the psychological effects that hair loss can have on women. Most women do not go bald, but some develop severe thinning of the vertex. A characteristic finding in androgenic female pattern hair loss is preservation of the frontal hair line. This form of hair loss is seen more commonly in the postmenopausal population.
Histology: Evaluation of a 4-mm punch biopsy specimen by the horizontal method is the best technique to evaluate hair loss. In androgenic alopecia, the follicles are normal in number, but they show evidence of miniaturization. Vellus hairs are increased in number. Whereas the normal scalp has been shown to have a vellus-to-telogen hair ratio of 1 : 7, the ratio in andro- genic alopecia is 1 : 3.5. The hair shaft diameters of the terminal hairs are inconstant, which corresponds to the miniaturization affect.
Pathogenesis: Androgenic alopecia has been shown to follow an autosomal dominant pattern of inheritance. It is believed to result from an abnormal response of the hair follicle to androgens (i.e., dihydrotestosterone). This androgen has been shown to cause miniaturization of the terminal hairs over successive hair cycles. As the hair follicles miniaturize, they become smaller with a thinner caliber. This causes less scalp coverage, which manifests as hair thinning. The actual hair follicles are not scarred or lost. Inhibition of the production of dihydrotestosterone from its precursor, testosterone, is one therapeutic tactic.
Treatment: Therapy for male pattern baldness includes use of the topical agent minoxidil 5%, applied twice daily, with or without the oral 5α-reductase inhibitor, finasteride. 5α-Reductase is the enzyme responsible for converting free testosterone into dihydrotestosterone. Both these agents have been shown in multiple randomized studies to decrease the rate of hair loss and increase the hair shaft diameter. These medications are well tolerated and have minimal side effects. Patients with prostate cancer should avoid the use of finasteride unless approved by their oncologist. The only option at present for women with androgenic alopecia is topical minoxidil 2%. This has been shown to decrease the rate of hair loss.
Most patients who use minoxidil experience a slowing of hair loss, and some see increased growth. It is critical to treat early in the course of disease to maximize the effects of the medication. Topical minoxidil may cause excessive hair growth on the forehead and temples if it is applied in these regions. This can be disconcerting for patients, and they need to be educated on the proper application of the medication.
Hair transplantation techniques continue to improve. The goal of surgery is to leave a natural-appearing hair pattern. This is best accomplished with minigrafts of 1 to 2 follicles at a time. A strip of the patient’s hair is removed from the occipital scalp, and each individual hair is dissected out. The separated hair follicles are then tediously inserted into the desired areas. Patients can have an excellent result, and the transplanted hair appear to be resistant to the effects of dihydrotestosterone.