Treatment of psoriasis and psoriatic arthritis with interferon gamma.

In a placebo-controlled double-blind randomized study, 24 patients with psoriatic arthritis were given 28 d of treatment, and in an open study, 56 patients were treated for 9 months. We treated patients with 100 micrograms IFN gamma per subcutaneous injections, which were given daily for the first 2 weeks and then 3 times per week. The principal criterion for evaluation of therapeutic success on arthritis was improvement of the Ritchie joint pain index by at least 25% in the double-blind and 30% in the long-term study. In the double-blind study, the interferon arm was superior to the placebo arm with a statistically significant, one-side error probability of less than 5% in the chi-square test. In the long-term study, IFN gamma caused an improvement in a portion of patients in the first 3 months of therapy. No further improvement was observed after the third month, and patients classified as responders in the first months showed a deterioration of the disease by continuing treatment. The humoral inflammatory parameters did not normalize during therapy. Regression of the skin manifestations could not be observed. IFN gamma is evidently capable of inducing a psoriasis on the injection site. Investigations of IFN gamma serum levels, IFN antibodies, 2'-5' A synthetase levels in serum, and mononuclear blood cells and NK cell activity under long-term therapy showed no explanation for the loss of efficacy after 3 months treatment.