Ankylosing Spondylitis Patients Have Higher Risk of Blood Clots, Study Suggests

Ankylosing spondylitis (AS) patients have a more than 50% increased risk of developing blood vessel clots, according to a population-based Canadian study.

“Clinicians should have an increased awareness of this complication so that they can provide the best care possible to their patients,” Antonio Aviña-Zubieta, PhD, a senior scientist of rheumatology at Arthritis Research Canada and the study’s lead author, said in a press release.

The study, “Risk of venous thromboembolism in ankylosing spondylitis: a general population-based study,” was published in the journal Annals of Rheumatic Diseases.

Axial spondyloarthritis refers to a group of rheumatoid diseases characterized by the involvement of the axial skeleton, the part of the skeleton made up of the bones of the head and torso. Ankylosing spondylitis is the most common disease in this group of disorders and presents with inflammatory back pain as it affects the spine — but can also involve other sites.

The prevalence of AS is about 0.2-0.3%, depending on the geographical distribution of human leukocyte antigen B27 (HLA-B27), the main genetic factor related to disease development.

Inflammatory diseases such as AS have been associated with a higher risk of venous thromboembolism (VTE) — blood clots that start in a vein. In these cases, the blood supply is compromised and represents a life-threatening complication if it occurs in a vital organ.

VTE includes both deep venous thrombosis and pulmonary embolism, depending on if the blockage occurs in the deep veins in the legs or in the lung arteries.

A small number of studies have observed a correlation between increased cardiovascular risk and overall mortality in AS. Even fewer records exist regarding the incidence of VTE in the AS population.

To investigate how VTE affects AS patients, researchers analyzed data from a provincial British Columbia, Canada, healthcare database from January 1996 to December 2012.

They identified 7,190 cases of AS. They also included 7,190 age- and sex-matched participants from the general population to serve as controls. The mean follow-up time was 6.2 years.

Results showed that compared with controls, AS patients had a 53% increased risk of VTE and a 63% higher risk of deep venous thrombosis. The risk of pulmonary embolism among AS patients was 36% higher than that of controls, but this difference was not statistically significant.

“These results expand on the findings of previous studies that implicate AS with vascular disease and add to the importance of controlling this inflammatory disease,” the researchers wrote.

Although not statistically significant, the analysis suggests that the risk for any of the three blood clot events — VTE, deep venous thrombosis, and pulmonary embolism — was highest in the first year after AS diagnosis.

Risk factors, such as body mass index (a measure of body fat), history of smoking, and use of anti-inflammation medicines, were not included in their analysis because they were absent from the database, according to the researchers.

“These results call for awareness of this complication, increased vigilance and preventive intervention by controlling the inflammatory process or by anticoagulation in a high-risk ankylosing spondylitis population,” Aviña-Zubieta said. “We now need to study whether or not inflammation-decreasing treatment could reduce the risk of this condition.”