SASDAS: a practical tool to measure disease activity in axSpa patients. Comments on “a prospective study of novel disease activity indices for ankylosing spondylitis”

Abstract

We read with interest the article “A prospective study of novel disease activity indices for ankylosing spondylitis” by T. G. Sundaram, et al. [1] This was an observational prospective study which aimed to explore the utility of two disease activity indices for patients with Ankylosing Spondylitis: the Simplified Ankylosing Spondylitis Disease Activity Score (SASDAS) and the Juvenile Spondyloarthritis Disease Activity Score (JSpADA). However, what brings us to write this letter is what seems to be a misconception of the development of the former score. Despite the fact that authors quoted the Sommerfleck et al. [2], as creators of the SASDAS based on erythrocyte sedimentation rate (ESR), they referenced Bansal et al. [3], as the developers of the C-reactive protein (CRP) SASDAS version, which is not accurate. We would like to briefly comment the chronology and history of SASDAS: in 2011, Sommerfleck et al. [4], from the rheumatology section at the Instituto de Rehabilitación Psicofísica (IREP) in Argentina, developed the SASDASESR and its cut-off values. Results of the analysis of 86 patients from a prospective cohort were published in 2012, showing an excellent correlation between this simplified index with ASDAS (based on ESR) and the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), and good correlation with other disease assessment measures, such as pain, Ankylosing Spondylitis Quality of Life (ASQoL) and Bath Ankylosing Spondylitis Functional Index (BASFI) [2]. One year later in 2013, Zamora et al. [5] from the same department, developed the SASDAS-CRP version showing again excellent correlation with the original indices, although this analysis was not immediately published. In the meanwhile, SASDAS-ESR with its original cut-off values was validated by Salaffi et al. [6] in an Italian cohort, proving once again the strong correlation between SASDAS-ESR and ASDAS-ESR and BASDAI, and a minor correlation with ASDAS-CRP and other measures tools. In this analysis, authors also assessed the cross-classification among the indices and found substantial agreement between them (although as expected, higher between SASDAS-ESR and ASDAS-ESR). In 2015, another validation of SASDAS-ESR was performed by Solmaz et al. [7] in 97 consecutive AS patients of two centres from Turkey, while they agreed about the strong correlation between the indices, they argued that the agreement between SASDAS-ESR and ASDAS-CRP was not good enough. In response to this manuscript, a letter by Schneeberger et al. [8] from the rheumatology section at IREP in Argentina, the original developer center, was published, stating that, even though the agreement between SASDAS-ESR and ASDAS-CRP was not optimal, neither was a very good agreement between the two versions of ASDAS. To support this argument, results from the performance analysis of the four indices (SASDAS ESR/CRP and ASDAS ESR/CRP) were showed as well as the SASDAS-CRP development process, results and its cut-off values. We hope that with this simple explanation you understand our astonishment after reading the two aforementioned Indian manuscripts and the necessity of clarifying this issue. Having elucidated the facts, we are pleased to see the interest these simplified measures have raised, and we encourage other cohorts to validate them, since we truly believe they are a very useful tool, especially nowadays that medical visits have less available time and there is a need to optimizing it. In conclusion, the simplified version of ASDAS (SASDAS) is a practical tool to measure disease activity in axSpa patients and it can be easily to use in clinical practice. Rheumatology INTERNATIONAL