Treatment of psoriatic arthritis complicated by systemic lupus erythematosus with the IL-17 blocker secukinumab and an analysis of the serum cytokine profile.

Psoriasis is a chronic disease of the skin that often affects the joints (psoriatic arthritis, PsA). Biologic agents such as TNF-α, IL-23 and IL-17 blockers have been proven to be quite effective against psoriasis and PsA, indicating the importance of those cytokines in the pathogenesis of the diseases. The importance of the IL-23/IL-17 axis has also been reported in systemic lupus erythematosus (SLE), but the safety and effectiveness of IL-17 blockers in SLE remain largely unknown. We encountered a patient with PsA and SLE. We treated him with an IL-17 blocker, secukinumab, and quantified the serum levels of various cytokines before and after the initiation of secukinumab therapy. As expected, the treatment was effective against the symptoms of PsA. No serious adverse events were observed in terms of SLE. Interestingly, serum IL-6 was substantially decreased after the initiation of therapy, whereas serum IL-17 was under the detection limit. These data indicate that IL-17 is produced locally, upstream of IL-6 production.