Molecular Characteristics of Sweet Syndrome: A Systematic Review.

Sweet syndrome (SS), originally described as acute febrile neutrophilic dermatosis, is a rare inflammatory skin condition, considered the prototype of neutrophilic dermatoses. It is characterised by the sudden onset of well-defined tender papules, plaques and nodules often accompanied by fever, neutrophilia and elevated markers of inflammation. Several variants have been described both clinically and histopathologically. Classifications include idiopathic, malignancy-associated, and drug-induced SS. The exact pathogenesis of SS is still unclear; however, recent findings have shed light on the role of dermal infiltrating neutrophils-in the context of innate immunity, and signalling pathways related to adaptive immunity. To critically analyse the current molecular landscape of SS and discuss the recent evidence supporting novel potential immune mediators and biological signalling pathways involved in SS pathogenesis. The methodology followed PRISMA guidelines and included two bibliographical databases, searching articles published until 17 December 2023. Titles, abstracts and full text were reviewed independently by two assessors, while other two investigators resolved any opinion differences. Of 3303 records identified through database search, 22 articles met the eligibility criteria for inclusion. We considered experimental studies that performed molecular analysis, in terms of cytokines quantification, gene expression and/or immunofluorescence/immunohistochemistry. As for the latter, only studies aimed at characterising the nature of the inflammatory infiltrate and potential mechanisms leading to distinct forms of cutaneous inflammatory cell influx were included. Overall, we described research on 202 SS patients (177 skin biopsies and 25 blood specimens) revealing the predominant role of neutrophil activation and abnormal proliferation as unifying mechanisms in different SS subtypes. Interestingly, we found that hyperactivation of the IL-1 pathway might occur only in a subset of SS patients and adaptive immunity could also play a role in the pathogenic scenario of SS, with a potential significant role of IL-17 axis. This systematic review provides a wealth of evidence on the molecular landscape of SS, although further research is needed to a deeper understanding of the patho-mechanisms of this rare disease and hopefully lead to targeted therapeutic approaches.