Background Axial spondyloarthritis (axSpA) includes both ankylosing spondylitis (AS) and axSpA with no definitive sacroiliitis on X-ray (non-radiographic axSpA, nr-axSpA).1 Several patient-reported outcome (PRO) instruments have been validated in AS. However, the use of such instruments in the broad axSpA patient (pt) population requires confirmation of their validity.
Objectives To evaluate the content validity and assess the psychometric measurement properties of PROs in the broad axSpA population.
Methods PROs assessed: Total and Nocturnal Spinal Pain Numerical Rating Scales, PtGA, BASDAI, BASFI, BASDAI fatigue and morning stiffness, ASQoL, and the SF-36. Published literature review, and both clinician and pt interviews, provided information on instrument content validity. Statistical analysis of measurement properties evaluated the reliability (test-retest, Spearman’s rank correlation; internal consistency, Chronbach’s alpha), responsiveness and construct validity. Measurement properties were assessed using data from the RAPID-axSpA trial (NCT01087762), which examined certolizumab pegol efficacy in axSpA treatment.2
Results Reviewed literature, mostly related to the AS sub-population, revealed a variety of relevant concepts: physical function, pain, disease activity, morning stiffness, fatigue, disturbed sleep, depression, mobility problems, problems performing recreational activities, household tasks, self-care and work-related tasks, and problems with social life/family relationships. The same concepts were evident for the overall axSpA population during expert and pt interviews. The reliability of all PRO instruments was satisfactory in the overall RAPID-axSpA population (N=325) and each subpopulation (AS n=178, nr-axSpA n=147): all test-retest correlation coefficients (Table) and internal consistency Cronbach’s alphas were >0.8. Correlations between measures were broadly as predicted from the concepts being elicited by the different scales, thus supporting the construct validity of the PRO measures. Validity was also supported by agreement between PRO measures and clinician-rated measures. All the PRO measures showed good sensitivity to change (effect size >0.8) at Weeks 12 and 24 for responders on almost all measures. No significant variations in psychometric properties were noted between the nr-axSpA and AS sub-populations.
Conclusions This study indicates that both the content validity and the measurement properties of PRO instruments used historically in AS are preserved in the broad axSpA population, including AS and nr-axSpA pts. Furthermore, these PRO instruments are valid in axSpA pts. Questions remain about relying on classical test theory for validation and the value of using generic outcome measures when well-developed disease-specific measures are available.
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Sieper J. Arthritis Rheum 2012;64(Supplement 10):S243
Acknowledgements The authors acknowledge Costello Medical Consulting for writing and editorial assistance which was funded by UCB Pharma.
Disclosure of Interest A. van Tubergen Grant/research support from: Abbott, MSD, Pfizer, Roche, Consultant for: Abbott, Pfizer, UCB Pharma, Speakers bureau: Abbott, MSD, UCB Pharma, P. Black Consultant for: UCB Pharma, Employee of: ERT, S. McKenna Employee of: Galen Research, G. Coteur Employee of: UCB Pharma