Psoriatic arthritis: clinical subgroups and histocompatibility antigens.

Histocompatibility antigens were determined in 60 patients with psoriatic arthritis. The patients were divided into clinical subgroups according to axial or peripheral joint involvement, disease severity based on number of peripheral joints involved, and the presence or absence of bone erosions. The total group showed a significant increase in frequency of HLA-A1, B17, B27, and DR7 when compared with a control population. The subgroup with spondylitis had a significant increase in frequency of HLA-B27 when compared with patients with peripheral arthritis (p less than 0.001). The subgroup with peripheral arthritis alone had a higher frequency of HLA-DR7 than the control group (p less than 0.001). There were also significant associations between HLA-DR7 and chronic severe disease (p less than 0.001) and between HLA-DR4 and the presence of erosions (p less than 0.05).