Psoriatic arthritis is a multifaceted disease, raising the discussion of its position between a single isolated disease or a part or subset of spondyloarthritis. New developments in the several fields of knowledge are paving the way for a new look at this disease.

A story of classification criteria

Several sets of criteria were proposed over the years for classifying psoriatic arthritis. Recent are the CASPAR criteria.1 The patient must have inflammatory articular disease (joint, spine or entheses) with three points from the following five categories: (1) evidence of current psoriasis or a personal or familial history of psoriasis; (2) typical psoriatic nail dystrophy; (3) absence of rheumatoid factor; (4) current dactylitis or a history of dactylitis; (5) radiographic evidence of juxta articular new bone formation. A score of 2 is assigned to current psoriasis; all other features are assigned a score of 1. These classification criteria allow the inclusion of many patients and various clinical phenotypes (including axial forms) in a definition of psoriatic arthritis. The question is if psoriatic arthritis fits into the spondyloarthritis frame too. Over the past few years, the ASAS group (Assessment in SpondyloArthritis international Society) developed and proposed new classification criteria for axial and peripheral forms of spondyloarthritis.2 These classifications allow the recognition of several clinical or phenotypical presentations of the disease3: axial spondyloarthritis, radiographic (corresponding to ankylosing spondylitis), non-radiographic; peripheral articular …