Pustular psoriasis and related pustular skin diseases

Patients with pustular psoriasis or related pustular diseases may have genetic abnormalities impairing the function of key players of the innate skin immune system. Recently, identification of these abnormalities has changed the paradigm of several of these diseases. These include generalized pustular psoriasis, palmoplantar pustular psoriasis and acrodermatitis continua of Hallopeau, and also drug-induced acute exanthematous generalized pustular eruption. Identified mutations in IL36RN, CARD14 and AP1S3 in different groups of patients lead to enhanced inflammatory cascade in several cellular subtypes including keratinocytes, and to the recruitment and activation of neutrophils and macrophages. These insights have unveiled pathophysiological features that shift the existing paradigms and emphasize the autoinflammatory nature of skin pustular disorders. They also highlight the crucial role of the innate immune system across entities belonging to the psoriasis disease spectrum, allowing identification of new appealing therapeutic targets. What's already known about this topic? Pustular psoriasis is an entity characterized by different clinical presentations, with palmoplantar pustular psoriasis (PPPP) and generalized pustular psoriasis (GPP) being the most emblematic subphenotypes. These disease variants are often refractory to available antipsoriatic treatments. Recently, significant advances have been achieved in the understanding of the pathogenesis of these diseases, due to the identification of causal genetic abnormalities in a monogenic model. What does this study add? This manuscript examines the mechanistic models underlying pustular psoriasis and its clinical expressions, and discusses the genotype-phenotype correlations in PPPP, GPP, acrodermatitis continua of Hallopeau and acute generalized exanthematous pustular eruption. The key role of dysregulation of the interleukin-36 pathway in these diseases paves the way for tailored drug development aiming to inhibit the inflammatory effects of these new members of the interleukin-1 family of cytokines.