Classification of clinical subsets in psoriatic arthritis.

The classification of PsA is controversial. Two recent papers have suggested new subgroup classifications, however both have served only to expand the controversy. In this study the clinical and radiologic features of 100 patients with PsA are recorded in order to examine possible clinical or radiologic features which may be associated with functional disability and to examine the usefulness of recent reclassification proposals in our patient population. Results indicate that an asymmetric oligoarthritis (AO) pattern of disease is most common occurring in 43%. A symmetric polyarthritis (SP) was present in 33%, and this subgroup had the highest number of erosions and deformities, and a higher proportion of patients with grade III/IV ARA functional disability. While the DIP joints were involved in 46%, predominant DIP joint disease occurred in 16%. As the DIP group had the shortest duration of arthritis, it may be that this group represents recent onset PsA which will evolve into one of the other subgroups. Sacroiliitis was a feature in 14% with predominant spondylitis (SPON) in 4%. Arthritis mutilans (AM) was rare occurring in only 2% of this population, perhaps representing patients with end-stage SP disease. Finally, 2% of patients had features of the synovitis-acne-pustulosis-hyperostosis-osteomyelitis (SAPHO) syndrome. A classification comprising just three subgroups (AO, SP, SPON) is proposed as being of most use clinically though a long-term prospective study is needed for verification.