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Donor Site Dominance in Action


#1

Donor Site Dominance in Action: Transplanted Hairs Retain Their Original Pigmentation Long Term

Dermatologic Surgery

Abstract

Donor dominance refers to autografts, which maintain their original characteristics (i.e., texture, growth rate, period of anagen) after translocation to a new site independent of the qualities of the recipient site. Since Dr Norman Orentreich introduced the term in 1959,1 it remains the fundamental concept underlying the success of hair transplants for conditions such as androgenetic and cicatricial alopecia. Recently, the influence of the recipient site on the growth and morphology of transplanted hairs has been discussed. We describe two patients who underwent autologous hair transplantation for androgenetic alopecia. Their donor hairs displayed prominent long-term pigmentary donor dominance despite being implanted into an area affected by graying. We propose that both donor and recipient sites play a role in hair transplantation and discuss possible mechanisms behind the preservation of pigmentation in hair transplantation.

Case Reports Case 1 A 40-year-old man presented with a 15-year history of androgenetic alopecia (Norwood-Hamilton Type Va) affecting his frontal scalp and vertex (Figure 1). He had no significant comorbidities and was not taking any medications. He also had prominent graying of the frontal scalp although occipital hairs were less affected. He had undergone two previous scalp reductions 10 year priors with a poor cosmetic result and obvious scarring. He underwent hair transplantation with an ellipse of donor tissue harvested from the occipital scalp. A total of 830 follicular units were transplanted to the frontal scalp and vertex. The majority of these donor hairs were pigmented. It is now 10 years since his hair transplantation and the donor hairs have retained their dark pigmentation despite being implanted into a region dominated by white hairs.

Case 2
A 50-year-old man presented with a 20-year history of Norwood-Hamilton Type IIIa androgenetic alopecia (Figure 2). He had no prior medical history apart from orthopedic operations, and he was a smoker of 15 cigarettes per day. He was treated with a hair transplant consisting of 1,300 follicular units, which were mainly pigmented donor occipital hairs. Now 6 years posttransplant, his frontal hairs have demonstrated pigmentary donor dominance by retaining their pigmentation despite being implanted in an area affected by canities.

Discussion
Androgenetic alopecia and hair graying are similar in that both progress in a characteristic pattern across the scalp. Graying is caused by a reduction or absence of melanogenic hair follicle melanocytes and incomplete melanocyte stem cell maintenance.2 Graying usually affects the temples first and spreads to the vertex and the rest of the scalp, appearing at the occiput last.3 Beard and body hairs are usually affected later.3 Similarly, in most subjects, androgenetic alopecia spreads in a wave from the frontal scalp to the occiput. Donor site dominance proposes that hair follicle characteristics are retained despite translocation, suggesting that individual hair follicles have different susceptibilities to common processes affecting the hair. Indeed, donor occipital hairs are more resistant to the balding process as they are hormonally insensitive and each hair follicle’s pigmentary potential is genetically regulated,3 leading to canities.

Recently, the role of recipient site dominance in hair transplantation has been discussed by several groups and although there are no studies with statistical significance demonstrating this, it is a fascinating challenge to our concept of donor dominance. Dr. Norwood first observed that donor hairs were able to take on the characteristic wave pattern of hairs in the recipient site.4 As it is not technically possible to surgically position hairs to create a wave pattern synchronized with neighboring hairs, this was strong evidence of recipient site dominance. Lee and coworkers5 treated madarosis (refers to loss of eyebrows/eyelashes) in patients with leprosy by hair transplantation and found evidence supporting recipient site dominance. In their patients, hairs transplanted to the eyebrows tended to have a slower growth rate and thicker hair shaft and were less likely to be affected by graying than hairs located in the donor occipital region.

Hwang and colleagues6 also suggested that the recipient site could influence donor hair characteristics. They showed that hairs transplanted from the occipital scalp to the lower leg took on the growth characteristics (i.e., growth rate, period of anagen) of leg hair and this partially reversed when hairs were then transplanted back to the nape of the neck. Interestingly, they propose that the altered growth rate upon transplantation is not due to adaptation to the recipient site over a period of time but apparently occurs immediately after transplantation and is maintained.6 In further experiments, hairs transplanted to other body sites including the back of the hand, lower back, and wrist developed a growth rate and anagen period resembling that of the recipient site.7 Hwang proposed that skin thickness and/or vascularity play a role in hair growth and survival. Further evidence of the existence of recipient site dominance was reported by Woods and Campbell.8 They performed an autologous hair transplant for androgenetic alopecia using donor chest hairs and discovered that hairs took on the length and wave characteristics of the recipient site with a prolonged anagen phase, more akin to scalp rather than chest hairs. In addition, Kossard and Shiell9 showed that hairs transplanted to treat androgenetic alopecia could be destroyed by new-onset scarring alopecia, indicating that donor hairs could still be targeted by inflammatory processes occurring at the recipient site.

A change in donor hair characteristics after autologous transplantation can be caused by follicular damage. Such damage can occur while sectioning harvested tissue and problems include tissue pressure causing distortion, inadequate magnification, dull cutting instruments, and drying.6 Transection of follicles can lead to thinner hair with a low growth rate.10 The survival and growth of transected hairs is directly related to the level of transection and depends on the preservation of the bulge stem cell region.11 Similarly, preservation of the follicular melanocyte stem cell niche in the area of the sebaceous gland may be required for normal hair follicle pigmentation. However, identification of the melanocyte stem cell niche can be challenging, even with the aid of a dissecting microscope. In our two patients, preservation of follicular pigmentation long term could be directly related to the intact nature of the melanocyte stem cells in donor hairs.

Improved hair growth can result from increased blood flow to hair follicles12 while a reduction in hair growth may be secondary to denervation.13 Severed neuronal connections during hair transplantation may explain why the graying rate of transplanted hairs is lower than that seen in the donor site.5 This hypothesis is based on the observation that the graying rate of scalp hair of a patient who underwent a unilateral sympathectomy to treat Raynaud’s syndrome was less on the sympathectomized side compared with the normal side.14

Although pigmentary donor dominance may be seen by experienced hair transplant surgeons, this is the first case documenting donor dominance influence on the pigmentation of donor hairs after transplantation to scalp affected by canities. We propose that both recipient and donor sites have influences on the donor hair growth and characteristics. It is possible that some aspects of hair growth after transplantation are more influenced by the recipient site rather than the donor site (and vice versa), and this remains to be investigated.


#2

Rather than labeling characteristics as donor dominance or recipient dominance, it may be helpful to be more accurate and specific. The characteristics in question depend on either follicular genetics or the environment the follicle is growing in.

As far as today’s research can show, Androgenetic alopecia is directly related to sensitivity to DHT. The level of sensitivity is controlled by the genes of that follicle.

Graying is caused by the genetic programing within melanocytes - pigment producing cells within the follicle. They are programmed to stop producing pigment at a specific time in the life cycle of the hair. As a human embryo develops, melanocytes migrate to developing skin at about 10 weeks gestation. These melanocytes can differ genetically, causing graying at varying times in the follicular life cycles.

Although androgenetic alopecia and graying can be observed progressing in a characteristic pattern across the scalp, it does not mean that the environment controls the process. Rather, it is the genetics and follicular structures in control here.

It is common for cells of identical genes to be found in groups, explaining why hair in different areas of the body can have similar characteristics. A few examples include: occipital hair that is not affected by androgenetic alopecia like frontal areas, temporal patches of hair that go gray before other areas, or patches of different colored fur on a calico cat. It may seem like the follicular environment is having the effect on these characteristics. However it is not an environmental consequence, but a genetic cause.

I say that the follicular genetics control the processes of androgenetic alopecia and graying. However, environmental factors can have an effect on the functioning of the follicle and thereby influence the speed and intensity of the gene-controlled processes. For example, periods of stress or malnutrition (environmental factors) can accelerate hair loss and graying.

Hair texture, length, growth rate, and period of anagen are characteristics more controlled by the environment in which the hairs grow. These characteristics are a result of the success of the functioning of the follicle. A richer environment will affect these factors.

Perhaps gardening is a good analogy. Lets say you have two identical rose bushes, and you plant one in a shaded area with dry soil, the other in rich soil with full sun exposure. Which one will grow taller? thicker? faster? Which one will have a longer growing season? If the bushes have a genetic propensity towards disease, which one will get sick first? These questions deal with characteristics more heavily influenced by environment.

Now consider if you took a red rose bush and transplanted it to a group of white rose bushes. Will the color of the roses change? If the rose bush has a genetic disease that causes it to stop blooming after 3 years, will this change depending on where you plant it? No because these are genetic properties, not environmental.

When people talk about donor dominance, they are really talking about the genetic characteristics of the hair vs. environmental effects. Its not 1959 anymore. We know a lot more about cellular structure, DNA and genes now. Perhaps we can update our language to push our medicine forward.