Both ASDAS and ADC are associated with spinal mobility in active axial spondyloarthritis: A comparison between early and later disease

Objective Using diffusion-weighted imaging (DWI)-derived apparent diffusion coefficient (ADC), we aimed to determine the relationship between intensity of spinal inflammation and mobility in patients with axial spondyloarthritis (SpA) in early and later stages of active disease. The Ankylosing Spondylitis Disease Activity Score (ASDAS) was also used for a more comprehensive evaluation. Methods Participants with axial SpA and back pain were recruited from 10 rheumatology centers. Clinical, biochemical and radiological parameters were collected. Short tau inversion recovery (STIR) sequence magnetic resonance imaging (MRI) and DWI of the spine and sacroiliac (SI) joints were performed. ADC maps were generated. Participants were examined for Bath Ankylosing Spondylitis Metrology Index (BASMI). Linear regression models were used to determine associations between BASMI and various clinical, radiological, and MRI parameters in participants with active inflammation on spinal ADC maps. Results One-hundred and twenty-seven participants were included in the analyses. Multivariate linear regression showed that mean ADC spine (ss = .16; P = .03), ASDAS-C-reactive protein (CRP) (ss = .29, P < .001), and ASDAS-erythrocyte sedimentation rate (ESR) (ss = .25, P < .01) were associated with BASMI. In participants with duration of back pain <= 3 years, mean spine ADC (ss = .37; P = .03), ASDAS-CRP (ss = .44; P = .01), and ASDAS-ESR (ss = .42; P = .01) were associated with BASMI after adjustment for confounding factors. In participants with duration of back pain >3 years, only ASDAS-CRP (ss = .25; P < .01) and ASDAS-ESR (ss = .20; P = .20) were associated with BASMI. Conclusion Intensity of inflammation and clinical disease activity were independently associated with impairment of spinal mobility. The associations were stronger in early (<= 3 years) than later disease.