Development and validation of an alternative ankylosing spondylitis disease activity score when patient global assessment is unavailable

Un nouvel article scientifique intitulé «Development and validation of an alternative ankylosing spondylitis disease activity score when patient global assessment is unavailable» a été publié dans le journal Rheumatology (Oxford).

Ortolan A, Ramiro S, van Gaalen F, Kvien TK, Landewe RBM, Machado PM, Ruyssen-Witrand A, van Tubergen A, Bastiaenen C, van der Heijde D.


To develop an alternative Ankylosing Spondylitis Disease Activity Score (ASDAS) to be used in research settings in axial SpA (axSpA) when Patient Global Assessment (PGA) is unavailable in databases.


Longitudinal data from four axSpA cohorts and two randomized controlled trials were combined. Observations were randomly split in a development (N = 1026) and a validation cohort (N = 1059). Substitutes of PGA by BASDAI total score, single or combined individual BASDAI questions, and a constant value, were established in the development cohort. Conversion factors for each substitute were defined by Generalized Estimating Equations, obtaining seven ‘alternative’ formulae. Validation was performed in the validation cohort according to the OMERACT filter, taking into consideration: (i) truth (agreement with original-ASDAS in the continuous score, by intraclass correlation coefficient and in disease activity states, by weighted kappa); (ii) discrimination [standardized mean difference of ASDAS scores between high/low disease activity states defined by external anchors, e.g. Patient Acceptable Symptom State; agreement (kappa) in the percentage of patients reaching ASDAS improvement criteria according to alternative vs original formulae]; and (iii) feasibility.


Comparing various options, alternative-ASDAS using BASDAI total as PGA replacement proved to be: truthful (intraclass correlation coefficient = 0.98, kappa = 0.90), discriminative [ASDAS scores between Patient Acceptable Symptom State no/yes: standardized mean difference = 1.37 (original-ASDAS standardized mean difference = 1.43); agreement with original-ASDAS in major improvement/clinically important improvement criteria: kappa = 0.93/0.88] and feasible (BASDAI total often available, as questions required for the ASDAS; conversion coefficient ≈ 1).


Alternative-ASDAS using BASDAI total score as PGA replacement is the most truthful, discriminative and feasible instrument.

Keywords: axial spondyloarthrits; disease activity; patient-reported outcomes; validation.

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