Nowadays, tumor necrosis factor-α (TNF-α) blockers are used for treatment of rheumatoid arthritis, inflammatory bowel diseases, ankylosing spondylitis, psoriatic arthritis, and psoriasis. Paradoxically, there are some reports on the appearance of psoriasis after administration of TNF-α blockers. Here, we report on a patient with monoarthritis in a knee joint who experienced psoriasis after TNF-α blocker therapy (adalimumab and etanercept). Oral medication was not a treatment option due to patient intolerance; thus, we tried ustekinumab, an anti-interleukin (IL)-12/23 monoclonal antibody used for treatment of psoriasis. Following ustekinumab injection, psoriatic skin lesions and joint symptoms were much improved. However, in the following period, joint pain and swelling became aggravated and synovial fluid cytokine levels including IL-6 and IL-17 were elevated. The treatment was changed to tocilizumab, a humanized monoclonal antibody against IL-6 receptor. After injection, knee joint swelling rapidly subsided without worsening of psoriatic skin lesions. (J Rheum Dis 2015;22:263-268)

Keywords: Tumor necrosis factor-α blocker, Monoarthritis, Psoriasis, Ustekinumab, Tocilizumab