LAUSR

539 sified as a localized form of pustular psoriasis. In addition, a recent report has revealed that there is no clear genetic difference between PPP and PPPP [4]. On the other hand, previous studies have demonstrated that neither PPP nor pustular psoriasis show any association with the PSORS1 locus, which is the strongest genetic risk factor for psoriasis vulgaris [5], and that both PPP and PPPP are molecularly different from psoriasis vulgaris based on transcriptome analysis [4]. Thus, it is assumed that the development of pustules on the palms and/or soles might be attributable to some disease-specific mechanism driven by the genetic differences between PPP/PPPP and psoriasis vulgaris, however, the distinction between PPP and PPPP has not yet been clearly elucidated. Recent studies have revealed that IL-17 plays important roles in pustular forms of psoriasis [6, 7]. Furthermore, in another study, positivity of IL-17A, IL-17C, and IL-17F was detected in palmoplantar pustular lesions, demonstrating the importance of other cells besides T helper-17 cells producing IL-17A and IL-17F [8]. These findings support the notion that brodalumab, an anti-IL-17 receptor A (IL17RA) antibody, is the most promising therapeutic option for pustular forms of psoriasis among the currently available biologic agents. Brodalumab binds with high affinity to human IL-17RA, which pairs with IL-17 receptor B, IL17 receptor C or IL-17 receptor E, and leads to a disruption in the IL-17 pathways by blocking the activity of IL-17A, IL-17C, IL-17E, and IL-17F. Indeed, in our case, although most of the patient’s skin lesions revealed a good response to secukinumab, an anti-IL-17A antibody, his palmoplantar pustular lesions were unresponsive to this biologic, and brodalumab further improved these refractory lesions, suggesting that the overexpression of other IL-17 family cytokines besides IL-17A contributed to the exacerbation and maintenance of the palmoplantar pustular lesions. In summary, we report the first case of PPPP successfully treated with brodalumab. Taken together with the current understanding of the pathogenesis of psoriasis, our case suggests that brodalumab might be a potent therapeutic option for pustular forms of psoriasis, including PPPP, and provides us with some useful clues to better understand the pathogenesis of this clinical variant in the context of IL-17 signalling pathways.