Classification and diagnostic criteria for psoriatic arthritis

The study of psoriatic arthritis is difficult and has lagged behind the study of other arthropathies in that there are no universally agreed or properly validated case definitions.This paper examined the validity and practicality of the original Moll and Wright criteria and subsequent criteria sets. Key features discriminating between psoriatic and other arthropathies were reviewed. A comparative study involving patients with psoriatic arthritis and rheumatoid arthritis was used to contrast the different classification methods.Although the Moll and Wright criteria continue to be widely used, they have been shown to discriminate poorly between psoriatic and rheumatoid arthritis. In comparison, the most sensitive criteria were those of Vasey and Espinoza, McGonagle et al, and Gladman et al (99%), whereas the others were significantly less sensitive (between 56% and 94%). The specificity of all methods was high and statistically similar (between 93% and 99%). Models that had reasonably good accuracy even without such key variables as psoriasis or rheumatoid factor were developed. Spinal involvement continues to be a key feature of psoriatic arthritis, but dissimilarities with classic ankylosing spondylitis have been highlighted.Further work is required to produce classification criteria for psoriatic arthritis. A prospective study collecting clinical, radiological, human leucocyte antigen (HLA) and immunological data from both psoriatic and non-psoriatic cases should provide agreed criteria for use in psoriatic arthritis studies in the future.