Psoriatic arthritis: outcome of disease subsets and relationship of joint disease to nail and skin disease.

Subgroups of PsA have been described but their relationship to the mode of onset of arthritis, to DIP joint disease and to nail and skin disease remains controversial. Therefore, the pattern of disease was documented in 100 patients with PsA in whom the mode of onset was known. The patients were divided into six subgroups: monoarthritis; DIP joint disease only; oligoarthritis; polyarthritis; spondyloarthropathy and arthritis mutilans. Sixty-four patients changed pattern. Nail disease (67% of total) was more common in patients with DIP joint disease (27% of total) and was significantly associated with adjacent DIP joint disease. Skin and nail disease severity did not correlate with joint severity, joint activity or functional status, nor differ between subgroups. Therefore, the mode of onset does not predict outcome in the majority. The topographic association of nail disease and involvement of the adjacent DIP joints suggests a common local inflammatory mechanism.