Paradoxical psoriasis following anti–TNF therapy in ankylosing spondylitis: A population-based cohort study

[...]we did not evaluate some variables that may contribute to the development of psoriasiform disease including smoking status and obesity. [...]patients with AS with higher disease activity could be assigned to the group treated with anti–TNF-α agents, and we cannot exclude the possibility that those patients might be associated more with psoriasis. [...]this study confirmed that the risk of new-onset psoriasis and PPP was significantly increased in patients with AS receiving anti–TNF agents.