Swedish researchers have found an increased risk of venous thromboembolism – blood clots in the veins – in people with rheumatoid arthritis beginning at diagnosis and persisting for at least 10 years.

Venous thromboembolism, or VTE, is a disease that includes both deep vein thrombosis and pulmonary embolism. Deep vein thrombosis, or DVT, is a blood clot that forms in one of the deep veins within the body, usually in the leg, blocking blood flow to the area and causing pain, redness and swelling. Pulmonary embolism, a life-threatening condition, occurs when a clot (usually from a DVT) breaks away and travels to the lungs, blocking blood flow and causing shortness of breath, pain and cough.

The new study, which appears in the October 3, 2012 issue of the Journal of the American Medical Association, compared more than 45,000 Swedes with rheumatoid arthritis, or RA, with members of the general population. The researchers found that among those with “prevalent” – or established – RA, the incidence of venous thromboembolism was twice that of the general population (2.2 percent vs. 1.1 percent over the 13-year study period).

But there is a bit of good news in the study for those with RA, says study co-author Marie Holmqvist, MD, PhD, a research fellow in the clinical epidemiology unit at the Karolinska Institute in Stockholm. Hospitalization – a traditional risk factor for serious blood clots, especially among people with autoimmune diseases such as RA – doesn’t further increase the risk. “These findings in combination are important,” Dr. Holmqvist says. “Because this means that although RA patients in general are at increased risk, there is no reason to fear that they are at extra high risk in conjunction with hospitalization, which has been suggested previously.”
 

And, it’s important to note, that the vast majority of RA study subjects did not suffer a blood clot during the study follow-up period. “Less than 3 percent of the RA patients had a blood clot,” Dr. Holmqvist says. “This is not extremely high, but comparable to the absolute risk of myocardial infarction [heart attack] that we and many others have reported previously.”

Still, Dr. Holmqvist suggests it’s a health situation that bears watching. “It might be that we need to start thinking about taking preventive measures to decrease the risk of this comorbidity. How [to do that] is trickier, since we know less about what is causing the increased risk,” she says.

Dr. Holmqvist says there are several hypotheses. “We know that acute inflammation [affects] coagulation factors that could be of importance in the formation of clots,” she explains. “We also know that RA patients smoke to a higher extent than the general population and that smoking is a risk factor for clots.”

Another risk factor, she says, is the fact RA patients generally have less mobility than their healthy counterparts. “So far, we don’t know. And one important future challenge is to find out why and how we can prevent it,” she adds.

So, what should an RA patient do with this information?

“I don’t think that patients with rheumatoid arthritis should be overly alarmed,” says Jack Ansell, MD, professor of medicine at New York University School of Medicine and Chair of the Department of Medicine at Lenox Hill Hospital, New York, N.Y. “The risk factor is still relatively low. But it’s important to know. And patients might want to ask their doctor, if they are hospitalized and have rheumatoid arthritis, whether they are at risk of developing blood clots.”

Dr. Ansell says the Swedish study is a good opportunity to focus on a deadly health problem many are not aware of: “Six hundred thousand people a year in the United States develop VTE,” he says. The Centers for Disease Control and Prevention reports that as many as 60,000 to 100,000 die annually of it.

“VTE is often a complication of another disease. So when somebody has cancer and they die of cancer, the fact is they may have died of a pulmonary embolism (blood clot in the lung) because blood clots are a major risk factor of cancer,” Dr. Ansell adds. “It’s important to get the message out that VTE is a medical problem people should be aware of,” he says.