Psoriasis and Psoriatic Arthritis Linked to Increased Gout Risk
Overlapping diseases can lead to missed opportunity to treat.
People with psoriasis or psoriatic arthritis are far more likely to develop gout – a painful form of inflammatory arthritis – than people without these conditions are, according to a large, prospective study published online recently in Annals of the Rheumatic Diseases.
Psoriasis is an inflammatory condition in which skin cells build up rapidly, causing thick, red skin overlaid with silvery patches called scales. An estimated 25 percent of people with psoriasis develop psoriatic arthritis, an inflammatory arthritis that causes painful, swollen joints in various parts of the body – especially the lower spine, fingers, toes and knees – and nail damage.
Lead study author Joseph Merola, MD, co-director of the Center for Skin and Related Musculoskeletal Diseases at Brigham and Women's Hospital in Boston, says his group, which runs a combined dermatology and rheumatology clinic, was in a unique position to observe patients with both disorders. “We looked at our referral base, and it became apparent that many patients referred to our clinic for inflammatory arthritis actually had gout,” he explains.
Dr. Merola and his co-authors noted that psoriasis, psoriatic arthritis and gout are all linked to unusually high blood levels of uric acid, a substance that forms when the body breaks down purines, which are found in human cells and in many foods. Uric acid is thought to be a byproduct of the rapid skin cell turnover and systemic inflammation that occur in psoriasis, and at least one study has shown a relationship between the severity of psoriasis and uric acid levels. Gout occurs when excess uric acid builds up in joints and the tissue around joints – often in the big toe but also elsewhere – and forms needle-like crystals, which can lead to sudden episodes of intense pain and swelling. If left untreated, gout can become chronic and lead to joint damage.
Because there is little research on the association between psoriasis (with and without arthritis) and the risk of gout, Dr. Merola and colleagues undertook a large-scale study of the subject. They drew participants from two large databases: the Health Professionals Follow-up Study, which collected health information on more than 51,000 male health professionals between 1986 and 2010, and the Nurses’ Health Study, which amassed similar information on nearly 122,000 female registered nurses between 1998 and 2010. All participants completed questionnaires about their medical history and lifestyle risk factors at the start of the study and at regular intervals throughout.
Participants who, in 2008, answered a question about physician-diagnosed psoriasis were included in this analysis. Of the nearly 28,000 men and 71,000 women who responded, 1,621 participants reported having psoriasis at the start of the studies, and an additional 1,334 reported developing psoriasis during the follow-up periods. Separately, 2,217 patients – 4.9 percent of men and 1.2 percent of women – developed gout during the follow-up periods.
After controlling for variables that can contribute to the development of gout – including a higher body mass index (often referred to as BMI), smoking, high blood pressure, type 2 diabetes, use of diuretics and eating certain foods – researchers found that the risk of developing gout was roughly twice as high in men and one-and-a-half times as high in women who had psoriasis than in those who didn’t.
Additionally, they found that for men and women with both psoriasis and psoriatic arthritis, the risk of developing gout was nearly five times greater, compared to participants with no psoriasis or psoriatic arthritis.
The researchers also wanted to know whether having any type of arthritis is linked to an increased risk of developing gout. But they found little relationship between having a history of rheumatoid arthritis and gout risk, and only a slight association between a history of osteoarthritis and gout risk, furthering strengthening the link between gout and psoriasis/psoriatic arthritis.
Dr. Merola says the study has important clinical implications for patients with psoriasis who suddenly develop inflamed joints. “For patients with psoriasis or psoriatic arthritis who are complaining of joint pain or recurrent tender, swollen joints, physicians should at least consider the possibility of gout, which is not a disease we typically screen for.” he says “We can check serum uric acid levels or make a diagnosis by putting a needle into a joint and extracting some fluid for analysis.”
Knowing what type or types of arthritis a patient has is important because it affects treatment choices. High levels of uric acid in psoriasis and psoriatic arthritis aren’t generally treated or even screened for, whereas taking medication on an ongoing basis to reduce levels of uric acid is a key treatment strategy for gout. And keeping all three conditions under control may help patients stay healthier in the long run; psoriasis, psoriatic arthritis and gout (as well as elevated levels of uric acid, called hyperuricemia) all have been tied to an increased risk of developing cardiovascular disease.
Dr. Merola is cautious in suggesting that psoriasis and psoriatic arthritis actually cause gout or that treating them might reduce gout flares. “Our findings suggest that there is a causal link between psoriasis, psoriatic arthritis and gout, but we can only say there is an association.
“Still, there should be an awareness that gout can occur at a higher rate among patients with psoriatic arthritis or psoriasis,” he says. “And it seems intuitive to infer that if we are very aggressive about treating psoriasis and controlling systemic inflammation, we can lower uric acid levels and prevent an intermittently debilitating gout condition.”
Jasvinder Singh, MD, a rheumatologist and associate professor in the division of clinical immunology and rheumatology at the University of Alabama, Birmingham, notes that a link between gout and high skin cell turnover in psoriasis was observed clinically several decades ago, but that the current study is the first to substantiate it.
“It certainly adds to our clinical observation and current knowledge,” he says. “If physicians and patients are aware of the high risk of gout in psoriasis, they might use preventive strategies – such as diet and lifestyle changes – to reduce the risk. How much we can reduce risk by changing diet and lifestyle remains to be seen, but we can employ that strategy. [In addition], this study will generate additional research into the basic mechanisms as to how and why the risk exists.”