High BMI Not a Factor in Axial Spondyloarthritis

Researchers say it is not necessary to take body mass index into account when assessing disease activity in axial spondyloarthritis patients.

The study appears in the June 16 issue of RMD Open.

Physicians primarily rely on two measures to assess axial spondyloarthritis (axSpA) and ankylosing spondylitis disease status:  the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and the Ankylosing Spondylitis Disease Activity Score (ASDAS). While BASDAI relies on patient-reported outcomes to measure ankylosing spondylitis in patients, ASDAS combines patient-reported outcomes with C reactive protein (CRP) to assess axial spondyloarthritis status.

Because adipose tissue is frequently associated with increased production of pro-inflammatory cytokines, such as C reactive protein, investigators hypothesized whether an elevated body mass index could be an accurate disease-activity indicator. Obesity, measured by body mass index (BMI), is associated with increased levels of C reactive protein (CRP). High levels occur in response to inflammation, including that associated with ankylosing spondylitis.  [[{"type":"media","view_mode":"media_crop","fid":"49677","attributes":{"alt":"©Custommedia/Shutterstock.com","class":"media-image media-image-right","id":"media_crop_9300284285116","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"6020","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"font-size: 13.008px; line-height: 1.538em; float: right;","title":"©Custommedia/Shutterstock.com","typeof":"foaf:Image"}}]]

Led by Roxana Rubio Vargas of the Leiden University Medical Center in The Netherlands, researchers found body mass index only influences CRP blood serum levels in women. But, the impact is not clinically relevant.

Knowing whether body mass index and excess adipose tissue contributed to CRP levels and self-reported outcomes could influence how providers guide patients on how best to control their axial spondyloarthritis.

Using patients and data from the existing SPondyloArthritis Caught Early (SPACE) cohort, launched in January 2009, researchers evaluated 428 patients over age 16 who had chronic back pain for more than three months, but less than two years. Investigators divided patients into normal weight (body mass index ≤24.9) and overweight (≥25). Collected C reactive protein levels of ≥5 mg/L were considered elevated.

Of the 428 patients, 168 (39.3%) fulfilled the Assessment in SpondyloArthritis International Society axial spondyloarthritis classification. This group had statistically lower rates of overweight and obesity- 18.4% and 11.9%, respectively - than those without the condition - 31.5% and 14.2%, respectively. Among patients with axial spondyloarthritis and those without, overweight patients had statistically significant higher C reactive protein rates (p=0.02 and 0.01, respectively). Researchers also discovered body mass index increases C reactive protein blood serum levels by 0.35 mg/L for each body mass index point – but only for women.

Overall, the researchers found, the impact of body mass index on C reactive protein in women isn’t enough to warrant using it as a measure of disease activity. It also doesn’t significantly impact any patient-reported outcomes.

“In general, it is not necessary to take BMI into account when assessing disease activity by ASDAS in axSpA patients with high BMI, but there may be a slight increase in ASDAS in female patients with very high BMI,” researchers wrote.

Further research into the influence of body mass index on CRP is needed, though. Researchers recommend conducting MRI and spectroscopy studies on a larger sample size of overweight women with axial spondyloarthritis to achieve more accurate results.

References:

Vargas RR, van den Bert R, et al. “Does body mass index (BMI) influence the Ankylosing Spondylitis Disease Activity Score in axial spondyloarthritis? Data from the SPACE cohort.” RMD Open. Published online June 2016. doi: 10.1136/rmdopen-2016-000283