Clinical Disease Activity Measures Associated With Trabecular Bone Loss in Axial Spondyloarthritis

Both elevated Ankylosing Spondylitis Disease Activity Score (ASDAS) and inflammatory markers are associated with trabecular bone loss among patients with axial spondyloarthritis (axSpA), according to research results published in The Journal of Rheumatology.

Researchers sought to determine the association between trabecular bone score and measures of clinical disease activity in patients with axSpA. They also investigated whether trabecular bone score values were related to disease activity measures over time. Patient data, including radiographs of the cervical, thoracic, and lumbar spine, dual-energy absorptiometry assessment, and patient questionnaires, were evaluated annually.

In total, 330 patients were enrolled in the study cohort of whom 240 were included in the analysis, based on available baseline and follow-up dual-energy absorptiometry assessment data. All patients (80% men) were aged between 20 and 67 years, and there were no significant differences in patient baseline data.

Overall, 199 patients (79%) fulfilled the modified New York criteria for the classification of AS. Mean ASDAS-Erythrocyte Sedimentation Rate (ESR) and ASDAS-C-reactive protein (CRP) were 2.7±1.1 and 2.4±1.3, respectively; 97 patients (41%) had syndesmophytes at baseline, and the mean trabecular bone score was 1.385±0.123.

Within the cohort, 7%, 17%, 18%, and 32% of patients in the inactive, low, high, and very high ASDAS-ESR activity groups, respectively, had a low trabecular bone score. Within the ASDAS-CRP group, higher disease activity was also associated with lower trabecular bone scores (P =.003 and P =.016, respectively).

Significant negative correlations were found between trabecular bone score and ESR, CRP, modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS), and syndesmophytes at baseline. Specifically, ASDAS-ESR was negatively correlated with trabecular bone score at years 1 and 2, while ASDAS-CRP was negatively correlated at 2 years only. The mSASSS and syndesmophytes number demonstrated “significant negative correlations” with trabecular bone score at all time points. Lumbar spine bone mineral density (BMD) showed a negative correlation with disease activity measures at baseline, whereas ESR negatively correlated with BMD only at the 2-year follow-up.

Univariate generalized estimating equation analyses demonstrated that statistically significant associations for all disease activity measures were longitudinally associated with trabecular bone score, excluding the Bath Ankylosing Spondylitis Disease Activity Index. In the univariate analysis, investigators found that age, smoking, radiographic sacroiliitis, and spinal structural damage were also longitudinally associated with trabecular bone score.

Among patients who fulfilled the AS criteria, ASDSAS-ESR, ASDAS-CRP, ESR, and CRP were all longitudinally associated with trabecular bone score, although trabecular bone score values decreased by 0.001 and 0.015 per 1-unit increase in both ASDAS-ESR and ASDAS-CRP, respectively.

Study limitations included the small sample size, particularly at years 3 and 4 because of both the short observation period and the relatively small number of patients with nonradiographic-axSpA who were included in the study.

“Clinical disease activity measures are longitudinally associated with trabecular bone loss, as assessed using the [trabecular bone score],” the researchers concluded. “We found a relationship between the [trabecular bone score] and disease activity in patients with AS, but not in those with nonradiographic-axSpA.”

Reference

Kang KY, Ju JH, Park S-H, Hong YS. Longitudinal association between trabecular bone loss and disease activity in axial spondyloarthritis: a 4 year prospective study [published online November 15, 2019]. J Rheumatol. doi:10.3899/jrheum.190749