SNOWMASS, COLO. – It’s now confirmed: obesity in psoriasis patients is a major independent risk factor for psoriatic arthritis.
This finding is actually good news. It opens the door to the potential prevention of psoriatic arthritis (PsA) through weight loss. Many psoriasis patients are obese and have the metabolic syndrome. And since a decade goes by on average between onset of psoriasis and development of joint disease, the prospect of a lowered risk of PsA could be a powerful motivator for heavy psoriasis patients to shed pounds, according to Dr. Christopher T. Ritchlin, professor of medicine and director of the Translational Immunology Research Center at the University of Rochester (N.Y.).
Dr. Christopher T. Ritchlin
That being said, it must be noted that there is as yet no solid evidence that weight loss actually lowers a psoriasis patient’s risk of developing PsA. A few studies are looking into whether weight loss makes a difference, but these investigations have been hampered – no surprise – by difficulty in getting patients to achieve and maintain significant weight loss, the rheumatologist noted.
Obesity is an established risk factor for psoriasis. The possibility that obesity among psoriasis patients is also a risk factor for PsA was raised in a study by investigators with the Utah Psoriasis Initiative, who found that self-reported increased body mass index (BMI) at age 18 years was associated with greater risk of PsA (Arch. Dermatol. 2010;146:721-6).
The Utah finding that greater obesity contributes to an increased risk of PsA has since been confirmed in an impressively large cohort study using data from The Health Improvement Network (THIN), a general practice electronic medical records database that includes more than 7.5 million U.K. patients. THIN is a newer database that is separate from the renowned U.K. General Practice Research Database, which has generated key findings on psoriasis as an independent cardiovascular risk factor.
At last year’s annual meeting of the American College of Rheumatology, THIN investigators reported that among 75,395 THIN enrollees with psoriasis followed for a mean of 5 years, 976 developed PsA.
The incidence of PsA was 23.09 cases/10,000 person-years in subjects whose first BMI measurement after diagnosis of psoriasis showed a BMI of less than 25 kg/m2. The incidence climbed stepwise with increasing BMI. Among subjects with a BMI of 25-29.9 kg/m2, the incidence was 25.37 cases/10,000 person-years. For those with a BMI of 30-34.9 kg/m2, it was 29.33 cases/10,000, while in those with a BMI of 35 kg/m2 or more the incidence of PsA was 38.04 cases/10,000.
In a multivariate analysis adjusted for potential confounders, the risk of developing PsA was 12% higher in subjects with a BMI of 25-29.9 than in those with a BMI below 25 kg/m2, 46% greater in those with a BMI of 30-34.9 kg/m2, and 75% higher in subjects with a BMI of 35 kg/m2 or more.
Dr. Ritchlin noted that a separate THIN analysis recently demonstrated that the prevalence of PsA climbs dramatically with more extensive psoriasis independent of other risk factors. This analysis included 4,539 middle-aged psoriasis patients. The overall prevalence of PsA was 8.4%. The lifetime prevalence of PsA was 4.5% among patients whose psoriasis involved 2% or less of their body surface area (BSA), 9.3% among those with 3%-10% BSA involvement, and 22.1% in subjects whose psoriasis affected more than 10% of their BSA.
"I know you’re all going to say, ‘Wait a minute, I have patients who have almost no psoriasis and yet have psoriatic arthritis.’ That’s very true. I have the same experience. But if you look at population-based data, the more severe your psoriasis, the more likely you are to get psoriatic arthritis," the rheumatologist declared.
He reported serving as a consultant to Abbott, Amgen, Centocor, Genentech, Targacept, UCB, and Wyeth and receiving research funding from multiple sources.