Diseases on Hair Follicles Leading to Hair Loss Part I: Nonscarring Alopecias

Katharina Wiedemeyer; Wolf-Bernhard Schill, MD; Christoph Löser, MD

Disclosures

Skinmed. 2004;3(4) 

In This Article

Androgenetic Alopecia

Androgenetic alopecia is the most common cause of hair loss in men and women (50%-80% of postpubertal whites). In men, a recession of the hairline in the frontoparietal region is observed, starting usually at age 30-40 years. Baldness of the vertex may follow. Male pattern baldness is often classified with the help of a system that was originally established by Hamilton in the 1950s and later modified in the 1970s by Norwood. Today we distinguish seven types with various subtypes to categorize the degree of androgenetic hair loss. In some cases, the hair loss is accompanied by pruritus, seborrhea and hirsutism -- the two last mentioned complaints both being typically androgen-driven conditions.

Women suffer from a more diffuse and usually less intense hair loss in the vertex region that starts after menopause due to the relative increase of androgens. The classification system for the female pattern designed by Ludwig is less complex. It includes three degrees of hair loss localized on the crown.

It is generally known that there is a strong concordance of the degree of baldness in fathers and sons, but predisposing genes are still unknown.[10] A polygenic inheritance is considered to be most likely. In androgenetic alopecia, the cycle of hair growth is accelerated, which results in a shortened anagen stage. The hair follicles produce thinner, shorter, and also depigmented hair shafts that can hardly be seen. This process is called miniaturization and is typical for androgenetic alopecia (vellus hair instead of terminal hair). Only a minority of follicles actually shed their hair shafts.

It is widely accepted that this process is related to an increased activity of 5--reduc-tase in males and of specific dehydrogenases in females within the dermal papillae. The enzymes convert testosterone (dehydroepiandrosterone in females) to dehydrotestosterone, which has a strong affinity to the androgen receptors of the papilla.[11] Interestingly, androgen-sensibility of hair follicles may lead either to hair loss or to hair growth referring to beard growth during puberty. It still remains unclear why androgens affect hair follicles differently at different body sites.

Androgenetic alopecia usually is a visual diagnosis confirmed by thorough history.[12] Measurable hormonal changes are rare. Of course, infrequent conditions, such as polycystic ovary syndrome, adrenal hyperplasia, androgen-producing neoplasms, or intake of exogen androgens (anabolics) have to be considered, especially when other symptoms of androgenization such as oligo-or amenorrhea, infertility of women, acne vulgaris, hirsutism, and virilization are observed.

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