Background It has been shown in the past that the spinal mobility in patients with axial spondyloarthritis (AxSpA) is associated with spinal structural damage, disease activity parameters and spinal inflammation . The impact of radiographic damage in the sacroiliac joints on functional parameters in patients with axial spondyloarthritis has not been investigated so far.
Objectives To analyze the association between radiographic sacroiliitis and parameters of the functional status and spinal mobility in patients with axSpA.
Methods Altogether 210 patients with definite axSpA (115 with radiographic and 95 with non-radiographic axSpA) from the German Spondyloarthritis Inception Cohort (GESPIC) were included in the current study. Radiographs of sacroiliac joints were obtained at baseline and after 2 years of the follow up and were scored by two trained readers according to the conventional grading system of the modified New York criteria (grade 0 to 4 per joint). A mean of two readers score for each joint and a sum score for both SIJ were calculated for each patient, giving a total sacroiliitis score between 0 and 8. Functional status and spinal mobility were assessed by means of the Bath Ankylosing Spondylitis Functional Index (BASFI) and the Bath Ankylosing Spondylitis Metrology Index (BASMI), respectively. Both baseline and year 2 data were included in the longitudinal mixed models analysis that was corrected for the dependencies between the two time-point values of each individual and adjusted for the structural damage in the spine (modified Stoke Ankylosing Spondylitis Spine Score - mSASSS), disease activity (the Bath Ankylosing Spondylitis Disease Activity Index – BASDAI and level of C-reactive protein – CRP), and sex.
Results In the longitudinal mixed model analysis adjusted for the presence of structural damage in the spine (mSASSS), disease activity (BASDAI and CRP) and sex, radiographic sacroiliitis demonstrated an independent association with the BASFI: β=0.10 (95% CI 0.01–0.19) and the BASMI: β=0.12 (95% CI 0.03–0.21), respectively – table. These data indicate that change by one radiographic sacroiliitis grade in one sacroiliac joint is associated with a BASFI/BASMI worsening by 0.10/0.12 points independently of structural damage in the spine and disease activity. Assuming linear association, progression of radiographic sacroiliitis from grade 0 bilaterally to grade 4 bilaterally would result in a worsening by 0.8 points in BASFI and 0.96 points in BASMI. Sensitivity analysis performed in radiographic and non-radiographic axSpA subgroups provided similar results for both outcomes.
Conclusions Radiographic damage in the sacroiliac joints might have an impact, although small, on spinal mobility and physical function in patients with axial SpA independently of structural damage in the spine and disease activity.
Machado P. et al. Ann Rheum Dis 2010; 69:1465–1470.
Acknowledgements GESPIC has been financially supported by the German Federal Ministry of Education and Research (BMBF). As funding by BMBF was reduced in 2005 and stopped in 2007, complementary financial support has been obtained also from Abbott/Abbvie, Amgen, Centocor, Schering-Plough, and Wyeth. Since 2010 GESPIC is supported by Abbvie.
Disclosure of Interest None declared
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