Newswise — BOSTON – Physically demanding jobs may increase the effects of inflammation on the progression of ankylosing spondylitis, possibly leading to increased bone formation in these patients, according to new research findings presented this week at the American College of Rheumatology Annual Meeting in Boston. Ankylosing spondylitis, or AS, is a type of inflammatory arthritis characterized by joint stiffness, pain and new bone formation that can result in partial or complete fusion of the spine. AS tends to develop in young adults, and tends to affect young men more often than young women. The prevalence of AS in the United States is estimated at 0.5 percent. A previous study in animal models showed that mice exposed to less mechanical stress developed less new bone formation. Researchers in the Netherlands, Belgium and France set out to investigate the same in humans and to learn if mechanical strain from physical activity might worsen bone formation in patients with AS.

Using data from 184 AS patients taken from the 12-year OASIS study, the researchers looked into the complex relationship between inflammation, mechanical stress and radiographic progression of disease in AS patients. Key factors in the study included job type, including sedentary white collar versus physically demanding blue collar, as well as smoking and socioeconomic indicators like personal income, family income and post-secondary education.

Patients had assessments with X-rays and disease activity, at baseline and at twice-yearly intervals throughout the study. Structural damage was measured using the modified Stoke Ankylosing Spondylitis Spine Score, or mSASSS and disease activity by the Ankylosing Spondylitis Disease Activity Score, or ASDAS. Seventy percent of the patients studied were male, 83 percent were HLA-B27 positive, 39 percent were smokers and 48 percent were blue-collar workers.

"We hoped to assess whether mechanical stress plays a role in new bone formation in AS. From a previous study we had conducted, we already knew that inflammation leads to radiographic damage. However, patients without inflammation also have some level of residual damage progression, so we were interested in other potentially explanatory factors, and that was where mechanical stress came into the scene,” said Sofia Romero, MD of the Amsterdam Rheumatology Center/University of Amsterdam in the Netherlands and a lead author on the study.

The results showed that both physical work and smoking amplified the effects of disease activity on C-ray progression. Among blue-collar workers versus white-collar workers, every additional unit of disease activity (one ASDAS unit) resulted in an increase of 1.2 vs 0.2 mSASSS-units per two years. In smokers versus non-smokers, every additional unit of disease activity resulted in an increase of 1.9 vs 0.4 mSASSS-units per two years. Personal income also significantly modified the relationship between disease activity scores and X-ray progression of disease, but education and family income did not.

The study’s authors concluded that strenuous physical activity in physically demanding, blue-collar jobs may amplify some of the effects of inflammation on disease progression in AS. They further concluded that this data may support the theory that mechanical stress leads to bone formation in AS. If further studies confirm this connection, rheumatologists may want to rethink the common recommendation for AS patients to do strenuous exercise, the authors noted.

"We need more research into this topic to unravel the precise role of mechanical stress and to disentangle this from the potential effect from smoking. Further research is also needed before recommendations are issued for patients, but it may be that certain types of exercise are more beneficial than others for patients with AS,” said Dr. Romero.

There were no specific funding sources for this study. It was supported by the departments where patients were recruited.

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The American College of Rheumatology is an international professional medical society that represents more than 9,500 rheumatologists and rheumatology health professionals around the world. Its mission is to Advance Rheumatology! The ACR/ARHP Annual Meeting is the premier meeting in rheumatology. For more information about the meeting, visit http://www.acrannualmeeting.org/ or join the conversation on Twitter by using the official #ACR14 hashtag.

Paper Number: 2828

A Physically Demanding Job May Amplify the Effect of Disease Activity on the Development of Syndesmophytes in Patients with Ankylosing Spondylitis

Sofia Ramiro1, A.M. van Tubergen2, Robert Landewé3, Annelies Boonen2, Carmen Stolwijk2, Maxime Dougados4, Filip Van den Bosch5 and Desiree van der Heijde6, 1Amsterdam Rheumatology Center/University of Amsterdam, Amsterdam, Netherlands, 2Maastricht University Medical Center, Maastricht, Netherlands, 3Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands, 4Université Paris René Descartes and Hôpital Cochin, Paris, France, 5Ghent University Hospital, Ghent, Belgium, 6Leiden University Medical Center, Leiden, Netherlands

Background/Purpose: We have recently shown that disease activity is longitudinally associated with radiographic progression in AS. In animal models, it has recently been shown that mice that were tail suspended, in order to prevent mechanical loading on paws, had less new bone formation, thus providing a proof-of-concept that mechanical strain drives new bone formation in spondyloarthritis. Our aim was to investigate the complex relationship between inflammation, mechanical stress and radiographic progression in patients with ankylosing spondylitis (AS), using job type as a proxy for continuous mechanical stress. Methods: Patients from OASIS were followed-up for 12 years, with 2-yearly assessments. Two readers independently scored the x-rays according to the mSASSS. Disease activity was assessed by the ASDAS-CRP. The relationship between ASDAS and spinal radiographic progression was investigated with longitudinal analysis, with job type at baseline (physically demanding (‘blue collar’) vs sedentary (‘white collar’) labor as a potential factor influencing this relationship. The effects of smoking status and socio-economic factors were also investigated.

Results: In total, 184 patients were included in the analyses (70% males, 83% HLA-B27 positive, 39% smokers, 48% blue-collar workers (65/136 patients in whom data on job type were available)). The relationship between disease activity and radiographic progression was significantly and independently modified by job type: In ‘blue-collar’ workers vs ‘white collar’ workers every additional unit of ASDAS resulted in an increase of 1.2 vs 0.2 mSASSS-units/2-years (p=0.014 for the difference between blue collar and white collar workers). In smokers vs non-smokers every additional unit of ASDAS resulted in an increase of 1.9 vs 0.4 mSASSS-units/2-years. Personal income also significantly modified the relationship ASDAS-mSASSS, but education and family income did not (Table).

Conclusion: Physically demanding jobs may amplify the driving effects of inflammation on radiographic progression, thus supporting the theory that mechanical stress leads to bone formation in AS. Smoking and personal income are likely classic confounders of this relationship but a separate detrimental effect of smoking on radiographic progression could not be excluded. If confirmed, these findings may have implications for our commonly given advice to patients with SpA to strenuously exercise.

Disclosures: S. Ramiro, NoneA. M. van Tubergen, NoneR. Landewé, NoneA. Boonen, NoneC. Stolwijk, NoneM. Dougados, NoneF. Van den Bosch, NoneD. van der Heijde, None