Anti-IL-17 monoclonal antibodies and bullous pemphigoid: treatment or causal agents? A case series and review of the literature.

Bullous pemphigoid (BP) is an autoimmune bullous disease, typically affecting the elderly, characterized by the production of autoantibodies directed against structural components of the dermal-epidermal junction. An association between BP and psoriasis has been described several times, but the mechanisms underlying this association have yet to be clearly defined. The pathophysiological mechanism underlying psoriasis may be implicated in the pathogenesis of BP, as psoriasis precedes BP in most cases; in particular, a promoting role has been hypothesized by biologic therapies, which may induce a switch from a T helper 1 (T_H1)/T_H17-dominant cytokine milieu, typical of patients with psoriasis, to a T_H2-dominant one, typical of patients with BP. IL-17 inhibitors, in particular, have also been successfully used to treat BP in patients with psoriasis. The use of these drugs in these patients has been based on in vitro studies. However, cases of new-onset BP or relapses of BP already diagnosed in patients with psoriasis treated with biologic drugs have also been reported, and they occurred mainly in patients on anti-TNF drugs, yet very few cases with anti-IL-17A drugs have been described. We hereby describe two cases of new-onset BP in two patients treated with anti-IL-17 drugs for psoriasis.