Smoking paradox in the development of psoriatic arthritis among patients with psoriasis

We have read with great interest the article by Nguyen and colleagues1 on the smoking paradox in the development of psoriatic arthritis (PsA) among patients with psoriasis. The authors present a large population-based study, in which they demonstrate that smoking is positively associated with PsA risk in the general population but negatively associated with PsA risk among patients with psoriasis, thereby suggesting that index event bias could result in the smoking paradox. The reasons for this smoking paradox are difficult to elucidate, but we agree with the authors’ emphasis on the …