Is there a therapeutic effect of botulinum toxin on scalp alopecia? Physiopathology and reported cases: A systematic review of the literature.

Botulinum toxin is a treatment whose effectiveness has been widely demonstrated in the treatment of facial wrinkles. Its use in alopecia has been much less studied in the literature. Therefore, we carried out a systematic review of the literature in December 2019 in order to index published cases of alopecia patients treated with botulinum toxin. Pub Med, Embase, and Cochrane Library databases were explored. Six studies that included 94 patients were selected. Only one study was prospectively controlled against placebo. Of the 94 patients, 85 were affected by androgenetic alopecia, 8 by alopecia areata, and 1 by radiation-induced alopecia. The doses injected per session varied between 30 and 150 units and the number of sessions between 1 and 12. In the majority of the studies, the injections were carried out in all the muscles of the scalp (frontal, temporal, peri-auricular, occipital). Four studies showed a frank improvement in hair growth. Two of them showed improvement in hair density using an objective endpoint (hair count). The remaining reported studies showed inconclusive results. Patient satisfaction was high across all studies, but this systematic review did not clearly demonstrate the value of using the botulinum toxin in the treatment of alopecia. Subsequent prospective randomized controlled studies are required.