Background Disease activity in SpA is widely evaluated through BASDAI or ASDAS with no proven superiority between the two, in spite the more objective evaluation of ASDAS through the inflammatory markers.
Objectives The aim of this study was to evaluate the clinical quality and discriminating power between the above indices when subdividing patients with anti-TNF therapy according to their disease status indicated by BASDAI, ASDAS or PtGA.
Methods This prospective, observational study included 100 patients with definite SpA on biological therapy.Demographic, clinical and laboratory data was collected. Statistical analysis was performed with SPSS 20.0.
Results When used as an external criterion PtGA showed that 12% of patients had active disease with a PtGA of over 5 while 88% were classified as low disease activity.Mean ASDAS-CRP and ASDAS-ESR in the active group were 3.39 and 3.24.Mean BASDAI score in the high activity group according to PtGA was 5.66.We showed that both ASDAS scores had good discriminating capacities, with similar values when using the SMD (2.0034 [95% CI 1.29–2.71]).Based on PtGA,BASDAI outperformed ASDAS scores with a SMD of 3.3391 [95% CI 2.5334–4.1447]. ROC curves of the disease activity scores by using the PtGA ≥5 as variable of high disease activity state showed the following: for ASDAS-CRP, ASDAS-ESR and BASDAI the AUCs (area under curve) were 0.89 (P=0.05; 95% CI 0.80–0.99), 0.88 (P<0.001; 95% CI 0.77–0.99), and 0.99 (P=0.009; 95% CI 0.97–1.00).For CRP and ESR the AUCs were 0.81 and 0.79. This shows the high accuracy of the three scores in assessing SpA activity,but with a lower fidelity of the inflammatory markers alone.When dividing patients according to BASDAI score,14% showed a more active disease than the rest of 86% who had low disease activity.Mean ASDAS-CRP scores in the first group was 3.31.When correlating disease activity scores for the entire study group we observed that BASDAI correlated to both ASDAS scores (r=0.65 and 0.71, P<0.001) and that PtGA showed a stronger correlation to BASDAI (r=0.912, P<0.01) than ASDAS and to acute phase reactants.
Conclusions This study shows that disease activity scores have good discriminatory powers. BASDAI surpassed ASDAS scores when relating to the PtGA. According to Van der Heijde et al.(1), the only situation in which BASDAI can outperform ASDAS is when assessing the PASS (patient acceptable symptom state). However, ASDAS-CRP had better discriminatory power than ASDAS-ESR or acute phase reactants. This demonstrates that ASDAS-CRP is a more objective evaluation that can better differentiate patients with high or low disease activity.
D van der Heijde,ASDAS, a highly discriminatory ASAS-endorsed disease activity score in patients with ankylosing spondylitis, Ann. Rheum. Dis,vol. 68,Dec 2009.
Disclosure of Interest None declared