Global functioning in axial spondyloarthritis is stronger associated with disease activity and function than with mobility and radiographic damage

Objective The Assessment of Spondyloarthritis International Society Health Index (ASAS HI) is a validated patient‐reported outcome (PRO) for global functioning of patients with axial spondyloarthritis (axSpA). The Epionics SPINE (ES) is an electronic device for assessment of axial mobility that provides an objective measure of spinal mobility by assessing range of motion (RoM) and range of kinematics (RoK). The aim of this study is to investigate the relationship between global functioning and clinical measures of disease activity, physical function, spinal mobility, and radiographic damage. Methods In a cross‐sectional study design, consecutive patients with radiographic and nonradiographic axSpA were included, and the following established tools were assessed: Bath ankylosing spondylitis (AS) disease activity index (BASDAI), Bath AS functional index (BASFI), Bath AS metrology index (BASMI), ASAS HI, and RoM and RoK using ES. Structural damage of spine and sacroiliac joints (SIJ) were assessed by counting the number of syndesmophytes and by New York grading of sacroiliitis. Kendall's tau correlation coefficients were calculated. Results In 103 patients with axSpA, ASAS HI scores correlated significantly with PRO scores (BASDAI, r = 0.36; BASFI, r = 0.48; and back pain, r = 0.41; all P < 0.001). In contrast, no significant correlation between ASAS HI and RoM and RoK ( r between −0.08 and 0.09) and radiographic damage in SIJ and spine (all r between 0.03 and 0.004) were seen, respectively. BASMI scores correlated weakly ( r = 0.14; P = 0.05). Conclusion This study shows that axSpA disease‐specific PROs have an impact on global functioning, whereas spinal mobility scores, even if objectively assessed by the ES, have limited impact on patient reported–global functioning. The results also suggest that global functioning is, in this cohort, not much dependent on the degree of structural damage in the axial skeleton.