To investigate the clinical course of disease over 2 years in patients with nonradiographic axial spondylarthritis (SpA) and patients with ankylosing spondylitis (AS).
The study group comprised 303 patients with axial SpA (158 patients with AS and a symptom duration of ≤10 years and 145 patients with nonradiographic axial SpA and a symptom duration of ≤5 years) who did not receive tumor necrosis factor (TNF) blockers during 2 years of followup.
The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) did not differ between patients with nonradiographic axial SpA and those with AS at any time point during followup. The Bath Ankylosing Spondylitis Functional Index was significantly higher in patients with AS at baseline only, but spinal mobility was generally better in patients with nonradiographic SpA compared with those with AS. At all time points, C-reactive protein (CRP) levels were significantly higher in patients with AS compared with patients with nonradiographic axial SpA. Accordingly, the Ankylosing Spondylitis Disease Activity Score (ASDAS) was significantly higher in the patients with AS at 2 of 4 time points. When patients with a BASDAI score of ≥4 plus an elevated CRP level at baseline were analyzed over time, there were no significant differences in the proportions of patients with nonradiographic axial SpA and those with AS who reached low disease activity status at ≥2 time points during 2 years of followup when a clinical definition of low disease activity was used (38% and 35%, respectively, achieved a BASDAI score of <4, and 13% and 15%, respectively, achieved a score of ≤2). When definitions that included the CRP level were used, however, a greater percentage of patients with nonradiographic axial SpA achieved low disease activity (25% of patients with nonradiographic axial SpA and 10% of patients with AS achieved a BASDAI score of <4 and a normal CRP level, and 13% of patients with nonradiographic axial SpA and 3% of those with AS achieved ASDAS-defined low disease activity).
Patients with nonradiographic axial SpA and those with AS who were not treated with TNF blockers demonstrated a similar clinical disease course over 2 years. Patients with nonradiographic axial SpA achieved a status of low disease activity more frequently than those with AS if outcome parameters that included the CRP level were used.