"This paper demonstrates that trauma and infection are risk factors for psoriatic arthritis (PsA) and smoking is 'protective,'" said Dr Dafna D. Gladman from the University of Toronto.
"It highlights the role of environmental factors in the development of psoriatic arthritis among patients with psoriasis and thus adds to our understanding, as these factors have been considered important but previous studies were not large enough to confirm that."
Dr Gladman and colleagues performed a case-control study of 159 PsA patients and 159 patients with psoriasis (but without PsA). Their findings appeared online May 10th in Arthritis Care & Research.
"This is the first study where patients with psoriasis were individually assessed to confirm the absence of psoriatic arthritis," Dr Gladman said.
On multivariable logistic regression analysis, three factors were significantly associated with PsA. Smokers were only half as likely as non-smokers to have psoriatic arthritis, whereas occupations that required lifting heavy objects increased the risk of PsA 2.92-fold and infections that required antibiotic treatment increased the risk 1.72-fold.
Having a history of injury nearly doubled the risk of PsA, but this association was of borderline statistical significance (p=0.054).
Factors found not to be associated with the risk of PsA included alcohol consumption, steroid treatment, vaccination, emotional stress, and female hormonal exposures.
"Patients with psoriasis should avoid heavy lifting so that they can avoid trauma if possible," Dr Gladman advised.
Recurrent micro trauma in physically demanding occupations can make these individuals more susceptible to PsA, her paper notes.
"We have already performed a further study with smoking which is currently under review and hopefully will be published soon," Dr Gladman said. "Smoking is indeed protective. The difficulty in understanding this is that smoking is a risk factor for psoriasis, but seems to be protective for psoriatic arthritis."
"We would certainly not recommend that they continue to smoke or start smoking to avoid the development of PsA," she added.
"We are currently planning to look at certain genetic factors which may be relevant to this observation," Dr Gladman said. "We are also following our psoriasis without arthritis patients prospectively and will be able to confirm this as causal over time."
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