Pathogenetic overview of psoriatic disease.

Psoriatic arthritis (PsA) is an inflammatory musculoskeletal disease with both autoimmune and autoinflammatory features. Evidence supports the distinct nature of PsA regarding its clinical, genetic, immunohistochemical, and imaging features. Such features can help to distinguish PsA from other common rheumatic diseases. Apart from peripheral joint involvement, the musculoskeletal lesions in PsA include enthesitis and involvement of the distal interphalangeal joint (frequently associated with nail involvement, dactylitis, and axial involvement). The traditional model of pathogenesis in PsA has identified it as an autoimmune disease; however, an alternative model classifies it as having autoinflammatory features. Similarly, there are important new genetic observations focusing on the HLA region, and genome-wide association that confirms the genetic heterogeneity of patients with psoriasis and patients with PsA. Newer imaging techniques have also provided a much more detailed characterization of tissue abnormalities, in particular highlighting the extent of new bone formation, which is quite distinct from rheumatoid arthritis.