Amplifying the concept of psoriatic arthritis: The role of autoimmunity in systemic psoriatic disease

Psoriatic arthritis (PsA) is a chronic inflammatory arthritis that may be present in near 30% of patients affected by psoriasis (PsO), clinically characterized by inflammation of periarticular (e.g., enthesis) and articular structures. Recently, an autoimmune footprint of PsA pathogenesis has been demonstrated with the presence of autoantigens and related autoantibodies in PsA patients' sera. In this context, histological features of PsA synovitis supports the relevance of an autoimmune pathogenesis of the disease. Since there is no currently validated test for PsA, the analysis of PsA synovial tissue revealed pathognomonic characteristics of PsA that may support the clinician in the clinical practice. PsA synovitis is characterized by a sublining infiltrate with T and B cells, vascular proliferation and a relative thin lining layer of proliferating intimal synoviocytes. PsA synovial histopathology shows that ectopic lymphoid-neogenesis with an increase of IL-23 expression. These new pathogenetics features and the systemic nature of the disease raised the concept of a Systemic Psoriatic Disease (SysPsD), characterized by multiple extra-cutaneous and -articular manifestations, highlightening the great heterogeneity of this condition. SyPsD represents a heterogeneous chronic inflammatory condition with a wide spectrum of phenotypical manifestations. The purpose of this review is to describe the new pathogenetic mechanisms and the different clinical pictures of SysPsD, with the ultimate goal of improving the knowledge of this heterogeneous chronic inflammatory condition.