Laboratory findings in patients with psoriasis, with special reference to immunological parameters, associations with arthropathy and sacro-iliitis.

Twenty-five male and 25 female consecutive patients hospitalized because of psoriasis were examined. The clinical and radiographical findings are presented in detail elsewhere. Increased serum IgA, C3, C4, and C3PA concentrations were found in patients both with and without arthropathy and/or sacro-iliitis. Increased IgG concentrations were found in patients without arthropathy, and of C1 inhibitor concentrations in patients with arthropathy and/or sacro-iliitis. IgG and IgA concentrations were lower in patients with arthropathy than in those without, the difference being most significant in patients with arthropathy of large joints. An association was found between increased C4 concentration and sacro-iliitis, increased CRP concentration and sacro-iliitis and increased C3 concentration and phalangeal joint arthropathy. C4 and CRP concentrations were not associated. A close association between CRP and SAA was observed. Our results indicate that psoriatic arthropathy is not a single uniform joint disease, but represents different forms of arthropathy.