A prospective study of novel disease activity indices for ankylosing spondylitis

There is an ongoing quest for robust disease activity measures in Ankylosing spondylitis (AS). Thus, we prospectively validated two new disease activity indices, Simplified AS Disease Activity Score (SASDAS) and modified Juvenile Spondyloarthritis Disease Activity Score (JSpADA). Patients with AS were assessed for BASDAI, ASDAS and other outcome measures at baseline and 3 months. Comparisons were drawn between those with juvenile onset, early disease and peripheral involvement, with the rest. Fisher's r to Z transformation was used to compare correlations. Receiver-operating characteristic (ROC) curves were used to calculate cutoffs for inactive, low, high and very high disease activity. Of the 107 patients (mean age-29 years) of 6-years long disease, 38.3% had a juvenile onset. SASDAS and modified JSpADA exhibited excellent correlation with BASDAI and ASDAS (all p < 0.001) and were higher in active vs. inactive disease. Treatment responders had a greater fall in SASDAS and modified JSpADA as compared to non-responders. The novel scores were higher in those with peripheral disease. Only SASDAS could discriminate early from late disease. Based on the previously proposed cutoffs, optimal scores for inactive, moderate, high and very high disease activity were deduced. SASDAS-CRP showed better internal consistency than SASDAS-ESR and correlated better with ASDAS-CRP in late disease (Z = 3.04; p = 002) and those with adult onset disease (Z = 2.18; p = 0.03). SASDAS and Modified JSpADA perform as well as standard complex scores and have potential for simpler daily use. From our analyses, SASDAS with CRP performs better than SASDAS-ESR, pending further validation.