Relationship of Psoriatic Arthritis to Other Spondyloarthritides.

In the early 1970s, Moll and co-workers formulated the unified concept of spondyloarthritides, a group of conditions sharing similar clinical features. Subsequently, criteria for their classification have been proposed by Amor and coworkers, the European Spondylarthropathy Study Group, and the Assessment in SpondyloArthritis international Society. Opinion, however, is divided between those who believe that the different entities of the complex represent the variable expression of the same disease ("lumpers") and those who think that these should be considered separately but under the same umbrella ("splitters"). Several sets of criteria have been proposed for psoriatic arthritis (PsA), the most recent being the ClASsification for Psoriatic Arthritis (CASPAR) criteria. According to some authors, there are persuasive arguments to support the view of PsA as a distinct entity.