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Scalp Pathology for the Hair Transplant Surgeon: Donor vs. Recipient Dominance: Revisited Bernard Nusbaum, M.D. In a previous issue of the Forum, I reviewed Dr. Norman Orentreich's original article which established the concept of “donor dominance” in androgenetic alopecia1. The finding that scalp autografts maintained their hair growth characteristics independent of the scalp recipient site has been the cornerstone of modern hair transplant surgery. This hypothesis was challenged by Hwang, et al2, who transplanted scalp follicles to the lower leg and showed that the survival rate and growth rate of transplanted hairs are influenced by the recipient site when the recipient site is other that the scalp. It is not surprising to see Dr. Orentreich's name as an author of a fascinating experiment recently published in the Journal of the American Academy of Dermatology which compared the growth of balding and non-balding human scalp follicles when transplanted onto immunodeficient mice3. Both male pattern and female pattern alopecia was studied. Scalp tissue was removed as 2mm punch grafts which were subsequently dissected into grafts containing no more than 2 follicles. All grafts underwent post-operative effluvium and initial regrowth within 7 weeks after transplantation. Measurements were made at 22 weeks. The results were astounding. In male pattern alopecia, the mean diameter of balding follicles increased 4-fold while the non-balding follicles decreased in mean diameter by 38%. At the end of the study the mean diameter between the two groups showed no significant difference. Balding and non-balding follicles grew in length at a similar rate consistent with the rate of human scalp hair growth resulting in nonsignificant differences in mean length at the end of the study. In female pattern alopecia, the mean diameter of balding hairs increased 3-fold while the non-balding follicles plateaued at approximately 50% of pretransplantation diameter. At 22 weeks, there were no significant differences in hair length between balding and non-balding follicles. Volume calculations showed a final balding hair volume double that of non–balding hairs. This report shows that miniaturized, androgenetic affected follicles can revert to terminal hair growth characteristics once removed from the human scalp. The same results were observed when male or female mice were used as recipients. The authors theorize that factors other than androgen withdrawal may be operative in this transformation but cannot exclude the possibility that differences in androgen levels or androgen availability between humans and mice may account for the phenomena observed. The fact that reversal of the miniaturized follicles occurred in one hair cycle may indicate that miniaturization in androgenetic alopecia may not occur over many hair cycles but may be a more abrupt process. The possible applications of restoring balding follicles to terminal hair status outside the scalp for the purpose of treating androgenetic alopecia seem endless. As usually occurs in science, significant findings are serendipitous. The original purpose of the authors was to develop a model for evaluating treatments for androgenetic alopecia. Their findings may, in fact, uncover hidden clues to discovering the pathogenesis of this condition in both men and women. References
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