Paradoxical Psoriasis and Worsening Spondylitis Due to Secukinumab in a Patient With Ankylosing Spondylitis: A Case Report and Literature Review.

Axial spondyloarthritis (axSpA) is an autoimmune disease primarily affecting the axial skeleton, with associated extra-musculoskeletal manifestations. Treatment strategies targeting cytokines tumor necrosis factor-alpha (TNF-α) and interleukin 17 (IL-17) have proven effective. However, paradoxical reactions, including paradoxical psoriasis and arthritis, have been reported in axSpA patients receiving TNF-α inhibitors. IL-17 inhibitors have been used as an alternative treatment option, but paradoxical reactions have also been rarely observed. This case report presents a 45-year-old man with axSpA who responded to infliximab for six years before discontinuing it due to secondary failure. After the washout period of infliximab, he was started on secukinumab but developed paradoxical psoriasis and worsening of inflammatory back pain after receiving the second loading dose which necessitated replacing it with upadacitinib. Complete resolution of paradoxical psoriasis and significant improvement in his back pain after three months ensued. This case contributes to understanding the complex dynamics in treating axSpA and managing paradoxical reactions.