Psoriatic arthritis in two patients with an inadequate response to treatment with tocilizumab.

Psoriatic arthritis (PsA) is considered as one of the seronegative spondylarthropathies. Like rheumatoid arthritis (RA), the increased production of interleukin (IL)-6 suggests a pathogenic role of IL-6 in PsA. However, whether humanized anti-IL-6 receptor antibody such as tocilizumab (TCZ) might be effective for PsA as well as RA has yet to be determined. We report herein two cases of PsA treated using TCZ. Although, TCZ treatment resulted in disappearance of serum CRP in both patients, arthritis and skin lesions were not improved despite 6-month administration of TCZ. In contrast, tumor necrosis factor (TNF) inhibitor proved effective against arthritis and skin lesions in these patients. Collectively, these findings not only indicate that IL-6 has distinct pathological roles in RA and PsA, but also suggest that TNF inhibitor therapy (but not TCZ) is effective for arthritis and skin lesions of PsA.