No abstract

Androgenetic alopecia affects both men and women. In men it produces male pattern hair loss with bitemporal recession and vertex baldness. In women it produces female pattern hair loss (FPHL) with diffuse alopecia over the mid-frontal scalp. FPHL occurs as a result of nonuniform hair follicle miniaturization within follicular units. Diffuse alopecia is produced by a reduction in the number of terminal fibres per follicular unit. Baldness occurs only when all hairs within the follicular units are miniaturized and is a relatively late event in women. The concepts of follicular units and primary and secondary hair follicles within follicular units are well established in comparative mammalian studies, particularly in sheep. However, discovery of these structures in the human scalp hair and investigation of the changes in follicular unit anatomy during the development of androgenetic alopecia have provided a clearer understanding of the early stages of androgenetic alopecia and how the male and female patterns of hair loss are related. FPHL is the most common cause of alopecia in women and approximately one-third of adult caucasian women experience hair loss. The impact of FPHL is predominantly psychological. While men anticipate age-related hair loss, hair loss in women is usually unexpected and unwelcome at any age. Treatment options to arrest hair loss progression and stimulate partial hair regrowth for FPHL include the androgen receptor antagonists spironolactone and cyproterone acetate, the 5α-reductase inhibitor finasteride and the androgen-independent hair growth stimulator minoxidil. These treatments appear to work best when initiated early. Hair transplantation should be considered in advanced FPHL that is resistant to medical treatments. Hair transplantation requires well-preserved hair growth over the occipital donor area. The psychological impact of FPHL may also be reduced by cosmetic products that improve the appearance of the hair. These agents work to minimize hair fibre breakage, improve hair volume or conceal visible bald scalp.

Diffuse hair loss in women with AA is due to a reduction in the number of terminal hairs per FU and an increase in the number of vellus hairs. This supports the hypothesis of a hierarchy of susceptibility within FUs to AA. Further investigation is required to ascertain whether secondary and tertiary hair follicles are more susceptible than primary follicles.

Background:Hair follicle miniaturization is the hallmark of male pattern hair loss (MPHL), female pattern hair loss (FPHL), and alopecia areata (AA). AA has the potential for complete hair regrowth and reversal of miniaturization. MPHL and FPHL are either irreversible or show only partial regrowth and minimal reversal of miniaturization. Hypothesis: The arrector pili muscle (APM) attachment to the hair follicle bulge, a recognized repository of stem cells may be necessary for reversal of hair follicle miniaturization.Materials and Methods:Sequential histological sections from MPHL, FPHL, AA, and telogen effluvium were used to create three-dimensional images to compare the relationship between the APM and bulge.Results:In AA, contact was maintained between the APM and the bulge of miniaturized follicles while in MPHL and FPHL contact was lost.Discussion:Contact between the APM and the bulge in AA may be required for reversal of hair follicle miniaturization. Maintenance of contact between miniaturized follicles in AA could explain the complete hair regrowth while loss of contact between the APM and the bulge in MPHL and FPHL may explain why the hair loss is largely irreversible. This loss of contact may reflect changes in stem cell biology that also underlie irreversible miniaturization.