13/05/2022
Male pattern baldness alopecia: Pathophysiology and clinical manifestations
Hair is not only one of the important factors that determine the attractiveness of appearance, but also the part that shows each person's personality. Thick, strong hair symbolizes vitality, strength and bravery of men. Thin hair, a lot of hair loss, and loose strands can indicate weakness that lowers a man's confidence. Hormonal alopecia areata is the most common type of hair loss in men. The forehead, top, and temples are common hair loss sites. In these areas, the hair becomes thin, reducing the diameter of the hair, and reducing the density of the hair. Overall, the negative psychological impact of male pattern baldness is less than that of female pattern baldness. But many men are very worried, guilty, low self-esteem, which significantly affects their quality of life when suffering from the disease. Some other terms are "male pattern baldness" and "male pattern hair loss", " Androgen alopecia in men” is used to refer to this condition.
1. Epidemiology
The age of onset of androgenic alopecia varies among men, but occurs on average in men in their 20s. Male pattern baldness is most common in middle age. The severity of male pattern baldness increases with age. This condition has not been observed in children before puberty possibly due to an androgen-dependent form of male pattern baldness. About 30% of Caucasian men are affected by the age of 30, at least 50% are affected. affected by age 50 and 80% affected by age 70. Incidence also varies by race: Caucasian men are more likely to experience baldness than other races such as Asian, American Indian, and African men.
2. PHARMACOLOGY
Normal hair growth occurs at the hair follicle level in a 3-stage cycle:
– Growth phase (anagen): 85% of hair is in the growth phase, active growth from 2 to 7 years. Hair is created continuously through the division and growth of keratin-producing epidermal cells that surround the dermal papilla at the base of the hair follicle.
Catagen phase: 1% of hairs are in the cessation phase, a 2 to 3 week transition during which the hair follicle shrinks as a result of programmed cell death.
– Telogen phase: This phase lasts from 2-3 months, accounting for 14%. After resting, hair will fall out. After the hair is shed, new hair will grow from the root and a new growth cycle will begin again.
In patients with alopecia areata there is a gradual decrease in the density of the terminal hairs (thick and pigmented) and a concomitant increase in the cilia of the hairs (short, fine, non-pigmented).
Hair loss in male pattern baldness, the growth phase is shortened and the regressive phase is prolonged or stays the same, the period of growth and regression phase is prolonged. The number of hair is reduced, even, the hair is long enough to not reach the scalp.
The cause of male pattern baldness is also not completely understood. This condition occurs as a result of a combination of increased androgenic activity on hair follicles that have a genetic predisposition (susceptibility gene).
The role of androgens is the most studied, specifically the androgen dihydrotestosterone (DHT). Dihydrotestosterone is synthesized from testosterone by type 1 and type 2 5α-reductases. 5α-reductase type 2, which is expressed in hair follicles and other androgen-dependent tissues such as the prostate gland, is more important than type 1. in male pattern hair loss.
The transition from the terminal hair to the filament is thought to be due to the shrinking of the hair follicle. Hair follicle shrinkage is caused by a hormone-regulated process in the bulbar part of the hair follicle. At the cellular level, dihydrotestosterone binds to the androgen receptor, and the hormone-receptor complex then activates the genes responsible for the gradual transformation of large, mature hair follicles into miniature hair follicles with growth period is shortened.
Several lines of evidence suggest an important role for androgens and DHT in male pattern baldness
- Bald hair loss is not seen in eunuchs who are androgen deficient. At the same time, the progression of male pattern baldness in men was halted when the men were castrated after puberty.
Bald-pattern hair loss is not seen in people with a deficiency of the 5α-reductase type 2 gene, or androgen receptor.
The scalp of people with alopecia areata contains high concentrations of 5α-reductase, DHT, and androgen receptors.
Hair loss is ameliorated by finasteride, a drug that inhibits the conversion of testosterone to DHT by selectively inhibiting type 5α-reductase activity.
Several susceptibility genes associated with male pattern baldness have been identified such as the androgen receptor (AR)/EDAR2 locus on the X chromosome, the PAX1/FOXA2 locus on chromosome 20p11 and the HDAC9 gene on chromosomes. body 7p21. Chromosome 3q26 may also have a pathogenic role.
Although androgen-mediated pathogenic mechanisms are the most identified and studied, other possible pathogenic mechanisms include Wnt signaling, prostaglandin D2 signaling, prostaglandin F2-alpha signaling, and Janus signaling kinase (JAK). New targeted therapies for male pattern baldness based on this mechanism are being studied and applied.
3. CLINICAL
Signs of male pattern baldness can appear as early as adolescence. The phenomenon of hair loss, thinning begins in the temples, forehead or crown area. The degree of baldness varies from person to person, some people have a lot of baldness on the top of the head, some people have more severe baldness in the forehead and temples.
The thinning hair gradually thins, often forming an M in front, at the frontal and temporal areas, and then at the top, leaving behind a rim and hair on the sides and occipital region of the head.
Many men with androgenetic alopecia areata present with itching. Itching may be a symptom of atopic dermatitis or a symptom of alopecia areata, which requires further research.
Hair loss classification
In 1951, Halminton first introduced a scale to classify male pattern baldness from types I-VIII. According to this scale, type I loses hair along the frontal margin, type II loses hair on the forehead and begins at the top of the occipital region. Type III, IV, V both fusion areas are connected, completely bald on the top, remaining hair on the sides and back of the neck into a rim from front to back. Then, Norwood added Hamilton's alopecia classification, adding types IIIa, IVa, Va, which are more pronounced at the hairline margins of the forehead, and type III vertex characterized by alopecia areata.
Not all men with male pattern baldness follow the Hamilton-Norwood scale hair loss patterns. About 10% of men have a phenotype similar to female alopecia areata (frontal hair loss and crown hair loss).
Other related diseases
Heart-related diseaes
Some studies show that male pattern baldness patients have a higher risk of cardiovascular diseases, hypertension, atherosclerosis, overweight, dyslipidemia, insulin resistance than the general population. shared. In addition, studies on the association between male pattern baldness and metabolic syndrome have mixed results. Currently, there are no guidelines for the screening and prevention of cardiovascular disease and metabolic syndrome for men with alopecia areata.
Prostate cancer
Studies evaluating the relationship between male pattern baldness and prostate cancer have mixed results. Some reports suggest that men with bald-pattern hair loss have an increased risk of prostate cancer, but there are no recommendations for prostate cancer screening in this man.
Skin cancer
Male pattern baldness is not life-threatening, but it can lead to physical harm. Hair is the outermost layer that contributes to protecting the scalp from ultraviolet rays, reducing mechanical injuries. People who are heavily bald may have an increased risk of sunburn and cell damage that leads to skin cancer. However, systematic studies of these adverse effects have not been confirmed.
Implementing the quadrants
Definitive diagnosis of male pattern baldness is usually based on clinical features of slow progression of hair loss, thinning and thinning of hair, typical pattern of hair loss.
– Histopathology: performed when it is necessary to differentiate with some other hair loss conditions. Changes in the ratio of hair follicles in the growth phase and in the regressing phase (A:T), the ratio of mature hair to the hair follicle (T:V). Many hair follicles decrease in size, almost completely atrophy.
– Dermoscopy: diverse hair diameter, hair follicles shrink, yellow dots around hair follicles, there are small areas without hair.
Differential diagnosis
- Hair loss in the stage of cessation of hair growth
– Diffuse regional hair loss
– Hair pulling
– Syphilis II…
CONCLUDE
Male pattern baldness is a common condition in males that usually develops gradually after puberty and is characterized by the loss of terminal hairs in the temples, forehead, and crown areas. This condition can have a negative impact on the psyche of the sufferer. Hormonal, genetic, and other factors contribute to the progression of male pattern baldness. The action of dihydrotestosterone on sensitive follicles contributes to hair follicle miniaturization, which clinically manifests as the replacement of terminal hairs by short, thin filamentous hairs.
The diagnosis of male hormone alopecia is usually clinical, with scalp biopsies being performed in some differentiated cases. This condition can also be associated with other disorders such as cardiovascular disease and cancer. prostate gland, metabolic syndrome. New therapeutic approaches with targeted effects based on other pathogenic mechanisms are being studied and applied.
