Common Baldness, Male pattern Alopecia

Androgenic alopecia is the commonest type of thinning or loss of the scalp hair in males. It was already described by Aristotle , who added that it did not affect women and children and that it did not occur in eunuchs. It is thus all the more surprising that this diagnostic perception was overlooked for centuries and that many completely unfounded theories on the aetiology of this type of alopecia were mean­while expressed. It is true that Sabouraud re­discovered the significance of masculine traits for the deve­lopment of alopecia in both males and females, but by wrongly interpreting the clinical signs he overestimated the signifi­cance of the seborrhoea which often accompanies alopecia and led to its being termed alopecia seborrhoica.

It was only quite recently that Hamilton drew atten­tion to the interaction of the male hormones and predisposing genetic and age related factors in the origin of androgenic alopecia and elaborated an exact method for the clinical evaluation of its extent.

Clinical Features and Incidence. In Hamilton’s stan­dard classification, the distribution of the scalp hair is divided into eight types, according to the course of the frontal and frontoparietal line and the incidence and extent of alopecia on the vertex. In the first three types there are no signs of vertical alopecia, while the other five comprise typical andro­genic alopecia of varying extent.

A simple posterior shift of the frontal hairline occurs in 96% of young males and 80% of females and is regarded as a physiological character of sexual maturation. Thinning of the hair above this limit and round the temples, however, which occurs in about 5% of Caucasians before the age of 20, is evalu­ated as the prodromal stage of androgenic alopecia.

The first stage of androgenic alopecia is characterized by frontoparietal recession of the hair — usually symmetrical — for a distance of more than 30 mm. The hair in the middle of the frontal line is diffusely thinner and the skin also shows through the thinning hair on the vertex. The most frequent incidence of this initial stage of androgenic alopecia is found in males between the ages of 20 and 30. If it does not appear until after 30 the prognosis is usually good, i. e. alopecia does not progress very quickly and may even stop altogether.

In the second stage of androgenic alopecia, the hair con­tinues to recede above the forehead and in the frontoparietal region and distinct — and usually rounded — alopecia appears on the vertex.

The third stage of alopecia, formed by progression of the
Course of androgenic alopecia preceding stage, is characterized by a bridge of hair high above the forehead, joining the two lots of parietal hair, or by a suprafrontal island of hair indicating the site of the original frontal hairline.

The fourth stage differs from the fifth only in respect or the extent of the “horseshoe” configuration of alopecia, in whicr. the ring of hair starts above the ears and encircles the oc­ciput. In the fourth stage there are still more than 100 lor.g terminal hairs on the area of alopecia and the marginal zones of the lateral parts are covered with relatively thick hair. Ir. the terminal fifth stage, there is no more hair on the vertex and the thin remaining hair consists of fine hairs with poor growth.

In striking contrast to the clinical picture of baldness, the chest and other parts of the body are often hypertrichotic. Ir. males, androgenic alopecia is also frequently accompanied :v indistinctly circumscribed patches of alopecia on the legs, in a peroneal localization. The course and extent of androgenic alopecia are highly individual and evidently depend on the genetic code and on age. Caucasian males are known to be predisposed to it; the pro­portion with different types is 12—15% and in 1—2% alopecia already develops at about the age of 30. Androgenic alopecia is less frequent in Negroes than in whites and in Mongolian males extensive alopecia is definitely uncommon.

Phylogenetic studies have shown that alopecia com­parable to human male pattern alopecia occurs in certain primates. Loss of hair, progressing from the upper limit of the eyebrows towards the vertex, appears in most adult chimpan­zees of both sexes and in all adult orangutans. The develop­ment of alopecia in the Stumptailed Macaque (Ma.ca.ca speciosa) is unwontedly striking in both sexes and histolo­gical, histochemical and other methods (e.g. the trichogramj have shown that in these primates it follows the same course as in man. Alopecia is thus not a disease in these animals, but a normal phenomenon, just as it is in man.

Aetiology. Androgenic alopecia in males is determined by genetic predisposition and by the presence of the male sex hormone testosterone. The testosterone level depends both on production of the hormone in the testis and on its further metabolism (chiefly in the liver). Since no direct relationship was found between the plasma or urinary testosterone level in men and the extent of alopecia, the processes determining the direct effect of androgens in sensitive cells were investigated. This led to discovery of the selective accumulation of dihydro testosterone (a metabolite of testosterone) by the cell nuclei and other microstructural cellular processes. Some authors sup­pose androgenic alopecia to be dependent on DHT control of adenylcyclase activity. Hormonal inhibition of adenylcyclase activity in alopecic parts of the head leads to a drop in the cAMP level, to resultant shortening of the anagenic phase and hence to transformation of the terminal hairs to a short, fine vellus.

Theories on the influence of testosterone on the develop­ment of male pattern alopecia leave many questions still un­resolved, but one thing is certain — this type of alopecia does not appear before puberty and males castrated before attain­ing sexual maturity always keep a straight suprafrontal hairline. If they are the offspring of subjects with alopecia, testosterone therapy induces various types of androgenic alopecia in them; if hormonal therapy is interrupted, alopecia is stabilized, whereas if it is resumed, alopecia again progresses.

According to contemporary opinion, the hair of the frontal line and the frontoparietal angles are true sexual hairs. If a genetically predisposed individual has a sufficiently high androgen level, a retrograde type of metamorphosis (Mon tagna’s term for the transformation of terminal hairs to vellus ) develops, with more or less pronounced male pat­tern alopecia as the outcome.

Although androgenic alopecia is evidently determined gene­tically, the exact type of heredity is still unknown. From the results of genealogical studies it is assumed to be an auto somally dominant character controlled by the sex chromosomes. Actually, its manifestation depends on the interaction of many genes (multifactorial heredity). Since in most cases alopecia appears between the ages of 20 and 30, it is presumed to be related to timed susceptibility of given cells to the presence of androgens.

The histological image of alopecia is characterized by a transformation process involving a large proportion of the follicles in the bald area. In the initial stage, elevated acid mucopolysaccharides activity can be demonstrated in the connective tissue sheath and the papilla, while intercellular oedema and hypervascularization are found in the corium and the subcutis. In the late phase, involution of all the structures in the corium and reduced enzymatic activity in the telogen follicles are present. During transformation of the terminal follicle to a miniature vellus producing follicle, the base of the follicle gradually shifts to the upper part of the corium, while the connective tissue sheath of the progressively shrink­ing follicle undergoes hyalinization and becomes sclerotic. The vellus follicles in foci of alopecia have the same in­nervation as anywhere else on the body, but the nerve plexi are adapted to the shorter length of the follicles. Enzymatic activity in the miniature follicle is unimpaired; it can thus be assumed that no significance can be attached to enzymatic dis­turbances in the genesis of alopecia and that transformation of the terminal hair to vellus is not the outcome of degenerative changes, but is evidently an irreversible process.

The ultrastructure of the vellus in foci of alopecia is virtually unchanged. Keratinization develops in the same way as in the terminal hairs of the scalp and is only quantitatively reduced. Trichograms made at the outset of alopecia show a raised percentage of club hairs (over 25%) in the frontal region and on the vertex. Dystrophic changes in the hair roots are less frequent and are evidently caused by accessory fac­tors. An increase in the number of club hairs in the marginal zones of alopecia is a sign of progression. The anagen phase of cyclic hair changes is curtailed in androgenic alopecia, as demonstrated by the relatively short hairs in the marginal zones.

Relationship of the sebaceous gland to androgenic alo­pecia. Although seborrhoea oleosa is described as an important concomitant process in male pattern alopecia, objective measurement of sebum production and of the size of the sebaceous glands in serial histological sections does not bear this out. On the contrary, the total number of sebaceous glands falls in foci of alopecia and mainly large and miniature glands dis­appear. Measurement of the amount of sebum showed its se­cretion in foci of alopecia to be the same as in normal skin; it was only more noticeable on bald, hairless skin.

Treatment. Despite the increase in knowledge of the aetio pathogenesis of androgenic alopecia, there is no known way of preventing or abolishing this condition. Since it is not a pathological process, but only a genetic mark, there is at present no successful prophylactic or therapeutic method against it. That is something which young men in particular find hard to accept and so, despite psychotherapy and ex­planation, most of them continue a vain search for medical aid or some “guaranteed” nostrum. Autograft experiments after Orentreich and the point transplantation of a few fol­licles suggested by Fujita held out some hope of success, but although grafts from the marginal hairy part take well on foci of alopecia, the ultimate cosmetic effect is not satisfac­tory and is of psychological rather than of practical signifi­cance.­

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