Psoriasis is a chronic autoimmune disease involving a complex network of cytokines such as interleukin (IL)-6. We tested the hypothesis that serum IL-6 level is a useful indicator of disease activity and predicts the treatment response to biologics in patients with psoriasis.
We analyzed 113 psoriasis patients treated with biologics (73 with infliximab [IFX], 24 with adalimumab [ADA], and 16 with ustekinumab [UST]) in our hospital. Disease severity was assessed using the Psoriasis Area and Severity Index (PASI) score, and Disease Activity Score 28 based on C-reactive protein (DAS28-CRP).
Before treatment, serum IL-6 levels significantly correlated with PASI scores in patients with psoriasis vulgaris (r = 0.432, p = 0.001) and with DAS28-CRP in patients with psoriatic arthritis (r = 0.469, p = 0.010). Serum IL-6 levels were significantly decreased by IFX (from 4.8 to 1.5) and ADA (from 2.5 to 1.4) therapy. In psoriatic arthritis, serum IL-6 levels at the endpoint tended to be lower in patients who achieved DAS28-CRP <2.3 (European League Against Rheumatism remission criteria) than in patients who did not.
Serum IL-6 level may be a useful biomarker for assessing disease activity in patients with psoriasis and for predicting responsiveness of joint symptoms to biologic treatment.