The Ludwig pattern of androgenetic alopecia is due to a hierarchy of androgen sensitivity within follicular units that leads to selective miniaturization and a reduction in the number of terminal hairs per follicular unit

Abstract

Hair follicles exist within follicular units (FUs). In utero the central primary hair follicles are surrounded by smaller secondary follicles. Each FU is nourished by a single arborizing arrector pili muscle that attaches circumferentially around the primary follicle with variable attachment to other follicles. Androgenetic alopecia (AA) miniaturizes susceptible scalp hair follicles in a distinctive and reproducible fashion manifesting in different patterns between men and women. We hypothesized that there is an additional layer to the patterning in AA, with a hierarchy of susceptibility within FUs to AA, and that the diffuse hair loss seen in women with AA is due to a reduction in the number of terminal hairs per FU rather than uniform miniaturization of entire FUs. We compared the mean numbers of FUs and terminal hairs per FU in 4-mm scalp punch biopsies in 24 women with AA with those in 21 controls. There was no significant difference in the number of FUs; however, women with AA had 2.40 terminal hairs per FU compared with 3.38 in the control group (P=0.0001) associated with a mean increase of 0.6 vellus hairs per FU. Complete miniaturization of all hairs within the FU was not seen. Diffuse hair loss in women with AA is due to a reduction in the number of terminal hairs per FU and an increase in the number of vellus hairs. This supports the hypothesis of a hierarchy of susceptibility within FUs to AA. Further investigation is required to ascertain whether secondary and tertiary hair follicles are more susceptible than primary follicles.