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Male Pattern Hairloss

Key Takeaways

More than 50% of all men over the age of 50 will be affected by AGA

Testosterone is converted into DHT which plays a key role in the initiation and progression of male pattern baldness

Male pattern baldness follows the well known progression pattern of starting at either the temples or the vertex (or both) and extending to the entire top of the scalp

most common form of hair loss in men with More than 50% being affected.

Male Pattern Hair Loss (Androgenetic Alopecia)

Androgenetic Alopecia (AGA) also known as pattern hair loss is the most commonly diagnosed form of hair loss in men causing significant physiological distress. Based on the data gathered by US National Library of Medicine, more than 50% of all men over the age of 50 will be affected by this disorder. While it is normal to loose around 50 – 100 hair follicles daily, AGA is categorized by excessive shedding of follicles that do not regrow to their normal condition.

While the exact cause of AGA is still debated, it is clear that pattern hair loss has a genetic factor and that the hormone Dihydrotestosterone (DHT) plays a key role.

DHT is a sex steroid and hormone produced in the body through the conversion of Testosterone into Dihydrotestosterone utilizing either one of the  5-alpha-reductance enzymes type I, II or III (5-AR-I , 5-AR-II or 5-AR-III) or the proteins GPSN2 and GPSN2L. while these proteins and enzymes are distributed in different tissues with varying degrees, It is estimated that up to 10% of the bodies Testosterone is converted into DHT.

DHT is a more potent sex hormone than Testosterone and it plays a major role in the development of sexual organs during fetal stage.

Testosterone is converted into DHT which plays a major role in AGA

DHT

It is clear that DHT plays a major role in AGA since it is documented that DHT attaches to the follicle receptor five times more efficiently than testosterone does. It is observed that castrated individuals and people who are genetically deficient in the 5-alpha-reductance enzymes do not develop pattern hair loss. Therefore it is believed that DHT attaches to the androgen receptors in the follicle causing miniaturization.

In order to understand how DHT impacts hair, first we need to understand the hair growth cycle. Hair follicles go through three phases in their cycle called anagen, catagen and telogen.

Anagen also known as growth phase is when the hair follicle is actively growing. This usually takes around 2 – 7 years for scalp hairs. Meaning the longer the hair follicle stays in this phase, the longer it will grow. It is estimated that around 80 – 85 % of hairs on the scalp are in this stage.

Catagen follows the anagen phase where the hair follicle falls out and new hair follicle begins to regenerate. This phase lasts for about 2 weeks.

Telogen also known as the resting phase is the final stage where the hair follicle remains dormant for up to 1 to 4 month in a healthy follicle. In a healthy scalp, around 12 – 20 % of hairs are in this phase.

After the telogen phase, the anagen phase begins again completing the cycle for a healthy hair follicle.

Hair follicles go through three phases in their cycle called anagen, catagen and telogen.

AGA occurs when the growth phase of the cycle is shortened leaving the follicle to spend most of its time in the resting phase. Consequently, the follicles become thinner over time and turn into vellus hairs (smaller thinner hair follicle).

 

This can be seen here in this microscopic image of a typical AGA affected scalp. 

In this picture, different stages of miniaturization can be seen in different follicles. While the healthy follicles are growing thick, the thinner shorter follicles right next to them are impacted by miniaturization. 

 

Furthermore, the end stage of miniaturization can also be seen in the follicles that are too small to be noticed with the naked eye. These are the small pimple like textures in in the scalp where a healthy thick follicle used to be.  

 

 

hair follicles affected by AGA will turn into miniaturized hairs which can be seen with a microscope.

AGA Presentation 

 

This miniaturization follows a unique and well known pattern which makes diagnosis of AGA straight forward. This pattern begins in temples and / or vertex and progress further through the rest of the scalp. The Hamilton-Norwood scale is used to determine the extent of this progression.

most common form of hair loss in men with More than 50% being affected.

One of the first signs of AGA is an unclear hair line as seen in the case of this patient.

This patient has a Hamilton-Norwood scale of I which is expected to further progress if no treatment is prescribed.

AGA progression leads to an unclear hair line border

As AGA progresses, it extends further into the temporal regions as well as effecting the vertex as seen in this patient.

This patient has a Hamilton-Norwood scale of III which is quite close to reaching a scale of IV.

as male pattern hair loss progresses, it leads to miniaturization in the crown.
REFERENCES
  • Hamilton JB. Patterned loss of hair in man; types and incidence. Annals of the New York Academy of Sciences 1951; 53:708-728
  • Olsen EA. Disorders of Hair Growth: Diagnosis and Treatment. New York: McGraw-Hill Inc.
  • Cash TF. The psychological effects of androgenetic alopecia in men. Journal of the American Academy of Dermatology 1992; 26:926-931
  • Budd D, Himmelberger D, Rhodes T, Cash TE, Girman CJ. The effects of hair loss in European men: a survey in four countries. European journal of dermatology : EJD 2000; 10:122-127
  • Langlois VS, Zhang D, Cooke GM, Trudeau VL. Evolution of steroid-5α-reductases and comparison of their function with 5β-reductase. General and Comparative Endocrinology. 2010;166(3):489–497
  • Olsen EA. Female pattern hair loss: Clinical features and potential hormonal factors. Journal of the American Academy of Dermatology 2001; 45:S70-80
  • Kligman AM. The human hair cycle. The Journal of investigative dermatology 1959; 33:307-316
    de Berker DAR, Messenger AG, Sinclair RD. Disorders of hair. In: Burns T, Breathnach S, Cox N, Griffiths C, eds. Textbook of Dermatology. Vol 4. 7th ed: Blackwell Publishing; 2004:63.68-63.10.
  • Courtois M, Loussouarn G, Hourseau C, Grollier JF. Hair cycle and alopecia. Skin pharmacology : the official journal of the Skin Pharmacology Society 1994; 7:84-89
  • Guarrera M, Rebora A. Anagen hairs may fail to replace telogen hairs in early androgenic female alopecia. Dermatology 1996; 192:28-31
  • Norwood OT. Male pattern baldness: classification and incidence. Southern medical journal 1975; 68:1359-1365

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