Identifying Flare Prone Spondyloarthritis: Insights From a Prospective Cohort

Background Flares are episodes of disease worsening requiring a change in treatment. Incidence of flares in spondyloarthritis (SpA) is around 60% in longitudinal patient-reported studies. The study was conducted to determine characteristics of flares in SpA and to identify differences between flare and non-flare populations. We hypothesized that the patient cohort who develop flares may behave differently in terms of validated disease activity and functional indices with regard to the non-flare population. Methods A cohort of 106 patients (2650 patient-weeks follow-up and 318 visits) who fulfilled the European Spondyloarthropathy Study Group (ESSG) or Assessment of SpondyloArthritis International Society (ASAS) classification criteria for SpA were followed up for six months. Diagnosis of flare was made by the rheumatologist using patient-reported indices and ruling out confounders. Statistical methods for analysis include the Mann-Whitney U test, ANOVA, chi-square, survival analyses, and longitudinal analyses by mixed-effects models, repeated measures ANOVA. Results At six months, 67 of 106 patients (63.2%) developed flares, of whom 51 (76.1%) had major (generalized) flares, and 16 (23.9%) had minor (localized) flares. In univariable analyses, shorter disease duration (<6 years), baseline enthesitis, baseline glucocorticoid use, and higher baseline disease activity were associated with increased odds of flare, whereas radiographic axial SpA was associated with reduced odds. In multivariable logistic regression analysis, inactive disease (OR: 0.21; 95% CI: 0.05-0.94; p = 0.042) and low disease activity at baseline (OR: 0.25; 95% CI: 0.09-0.72; p = 0.011) were independently associated with lower odds of flare, while baseline enthesitis was associated with higher odds (OR: 11.29; 95% CI: 1.30-93.46; p = 0.025). The median time to flare was longer in patients receiving biologic or targeted synthetic DMARDs (88 days vs 26 days), although this difference did not reach statistical significance (p = 0.249). Longitudinal analyses using general linear and mixed-effects models demonstrated significant differences in trajectories of ASAS-validated indices between flare and non-flare groups. Conclusion Baseline disease activity and enthesitis status are key determinants of flare risk in SpA. Patients with inactive or low disease activity have lower odds of flare, whereas the presence of enthesitis is associated with increased risk.