Determinants of the Physician Global Assessment of Disease Activity and Influence of Contextual Factors in Early Axial Spondyloarthritis

Abstract

Objective: To investigate determinants of the physician global assessment (PhGA) of disease activity and the influence of the contextual factors on this relationship in patients with early axial spondyloarthritis (SpA). Methods: Five-year data of DESIR, a cohort of early axial SpA, were analyzed. Univariable generalized estimating equations (GEEs) were used to investigate contributory explanatory effects of various potential determinants of PhGA. Effect modification by contextual factors (age, sex, and educational level) was tested, and if significant, models were stratified. Autoregressive GEE models (i.e., models adjusted for PhGA at the previous time point) were used to confirm a longitudinal relationship. Results: A total of 708 patients were included. Higher Bath Ankylosing Spondylitis Disease Activity Index individual questions, swollen joint count in 28 joints (SJC28), tender joint count in 53 joints, Maastricht Ankylosing Spondylitis Enthesitis Score, C-reactive protein (CRP) level, and Bath Ankylosing Spondylitis Metrology Index score were associated with a higher PhGA. Sex and age were effect modifiers of SJC28; the contributory effect of SJC28 was largest in the younger male stratum (β = 1.07 [95% confidence interval (95% CI) 0.71, 1.43]), and the smallest in the older female stratum (β = 0.13 [95% CI 0.04, 0.22]). Autoregressive GEE models revealed the same determinants as having a longitudinal association with PhGA and the same pattern of effect modification. Conclusion: Patients’ subjective symptoms, peripheral arthritis and enthesitis, higher CRP level, and impaired spinal mobility contribute to explaining PhGA in patients with early axial SpA, irrespective of sex and age. Intriguingly, physicians consider the presence of swollen joints as more important in males than in females.