CHICAGO – Overweight and obese psoriasis patients have it within their power to reduce their risk of developing psoriatic arthritis through weight loss, according to a large British longitudinal study.
Bruce Jancin/MDedge News
Dr. Neil McHugh
Of the three modifiable lifestyle factors evaluated in the study as potential risk factors for the development of psoriatic arthritis in psoriasis patients – body mass index, smoking, and alcohol intake – reduction in BMI over time was clearly the winning strategy, Neil McHugh, MD, said at the annual meeting of the American College of Rheumatology.
The message from this study of 90,189 incident cases of psoriasis identified in the U.K. Clinical Practice Research Datalink was unequivocal: “If you’re overweight and have psoriasis and you lose weight, you reduce your chance of developing a nasty form of arthritis,” said Dr. McHugh, professor of pharmacoepidemiology and a rheumatologist at the University of Bath, England.
“As psoriatic arthritis affects around 20% of people with psoriasis, weight reduction amongst those who are obese may have the potential to greatly reduce their risk of psoriatic arthritis in addition to providing additional health benefits,” he added.
Among the more than 90,000 patients diagnosed with psoriasis, 1,409 subsequently developed psoriatic arthritis, with an overall incidence rate of 2.72 cases per 1,000 person-years. Baseline BMI was strongly associated in stepwise fashion with subsequent psoriatic arthritis. Psoriasis patients with a baseline BMI of 25-29.9 kg/m2 were at an adjusted 1.76-fold increased risk of later developing psoriatic arthritis, compared with psoriasis patients having a BMI of less than 25. For those with a BMI of 30-34.9 kg/m2, the risk of subsequent psoriatic arthritis was increased 2.04-fold. And for those with a baseline BMI of 35 kg/m2 or more, the risk was increased 2.42-fold in analyses adjusted for age, sex, psoriasis duration and severity, history of trauma, and diabetes.
In contrast, the risk of developing psoriatic arthritis wasn’t significantly different between psoriasis patients who were nonsmokers, ex-smokers, or current smokers. And while there was a significantly increased risk of developing psoriatic arthritis in psoriasis patients who were current drinkers, compared with nondrinkers, the risk in ex-drinkers and heavy drinkers was similar to that in nondrinkers, a counterintuitive finding Dr. McHugh suspects was a distortion due to small numbers.
While the observed relationship between baseline BMI and subsequent risk of psoriatic arthritis was informative, it only tells part of the story, since body weight so often changes over time. Dr. McHugh and his coinvestigators had data on change in BMI over the course of 10 years of follow-up in 15,627 psoriasis patients free of psoriatic arthritis at the time their psoriasis was diagnosed. The researchers developed a BMI risk calculator that expressed the effect of change in BMI over time on the cumulative risk of developing psoriatic arthritis.
“We were able to show that if, for instance, you started with a BMI of 25 at baseline and ended up with a BMI of 30, your risk of psoriatic arthritis goes up by 13%, whereas if you start at 30 and come down to 25, your risk decreases by 13%. And the more weight you lose, the greater you reduce your risk of developing psoriatic arthritis,” the rheumatologist explained in an interview.
Indeed, with more extreme changes in BMI over the course of a decade following diagnosis of psoriasis – for example, dropping from a baseline BMI of 36 kg/m2 to 23 kg/m2 – the risk of developing psoriatic arthritis fell by close to 30%.
Dr. McHugh reported having no financial conflicts regarding this study, funded by the U.K. National Institute for Health Research.
SOURCE: Green A et al. Arthritis Rheumatol. 2018;70(Suppl 10): Abstract 2134.