ANDROGENIC ALOPECIA
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.
