Smoking is positively associated with the risk for psoriatic arthritis (PsA) in the general population, but negatively associated with PsA in patients with psoriasis, according to the results of a recent cohort survival analysis published in the Annals of the Rheumatic Diseases. Researchers sought to clarify the methodologic mechanisms underlying this paradox.

The investigators utilized data from the Health Improvement Network between 1995 and 2015 to perform their analysis, which examined the association between smoking and the development of incident PsA in the general population and in patients with psoriasis. A total of 225,213 participants with incident or prevalent psoriasis and 7057 participants with incident PsA were identified over a mean of 7.0 years. The average patient age in the overall study population was 42 years, 53% of the participants were women, 13% were obese, and 62% were current drinkers at baseline.

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Approximately 56% of the participants were nonsmokers, 16% were ex-smokers, and 28% were current smokers. In patients with psoriasis, the average age was 45 years, 52% were women, 21% were obese, and 64% were current drinkers. Moreover, approximately 46% of participants with psoriasis were nonsmokers, 19% were ex-smokers, and 35% were current smokers.

Smoking was associated with an increased risk for PsA in the general population (adjusted hazard ratio [HR], 1.27; 95% CI, 1.19-1.36) but with a decreased risk for PsA in patients with psoriasis (HR, 0.91; 95% CI, 0.84-0.99). Mediation analysis indicated that the effect of smoking on the risk for PsA was mediated almost entirely by its effect on psoriasis.

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The investigators concluded that the use of a traditional study design and analytic methodology might be associated with a risk factor paradox when examining smoking and risk for PsA. Additional research is warranted to identify an appropriate study design and analytic method to help ascertain the total effect of smoking on the development of PsA in patients with psoriasis.

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Nguyen UDT, Zhang Y, Lu N, et al. Smoking paradox in the development of psoriatic arthritis among patients with psoriasis: a population-based study [published online November 4, 2017]. Ann Rheum Dis. doi:10.1136/annrheumdis-2017-211625