Topical Minoxidil in Alopecia Areata: No Effect on the Perifollicular Lymphoid Infiltration

The therapeutic value of topical minoxidil in alopecia areata (AA) has been investigated in recent years, with variable results. Although the mechanism whereby minoxidil may stimulate hair regrowth in some cases of AA has not yet been elucidated, there have been reports of a decrease in the perifollicular infiltrates of mononuclear leukocytes (MNC) - particularly T lymphocytes - that characterize this condition, in patients “responding” to topical minoxidil. In a randomized and double-blind study, we have investigated the effect of 5% topical minoxidil versus placebo (vehicle alone) on the extent and composition of the perifollicular MNC infiltration in 20 patients having extensive AA (26-99% scalp hair loss). The proportions of hair follicles showing perifollicular infiltration by MNC and their main subsets were determined with histologic and immunohistochemical stainings of scalp biopsies obtained before treatment, after 12 weeks of randomized double-blind minoxidil versus placebo treatment, and after 12 additional weeks during which all patients received minoxidil. Six of the patients showed cosmetically acceptable hair regrowth (CAHR) at the end of the 24 weeks and this was associated with a significant decrease in the proportions of follicles infiltrated by total T and B lymphocytes, macrophages, and Langerhans cells at week 12, and by total T lymphocytes at week 24. However, no significant differences in the extent or composition of the perifollicular infiltrates were detected at week 12 between patients receiving minoxidil and placebo, or between the week-12 and week-24 biopsies of those patients who first received placebo and then minoxidil. These findings indicate that in AA the reduction in perifollicular T-cell infiltration associated with CAHR is not attributable to an effect of topical minoxidil.