Patient-assessed health in ankylosing spondylitis: a structured review

Objective. To review evidence relating to the measurement properties for all disease-specific, multi-item, patient-assessed health instruments in patients with ankylosing spondylitis (AS). Methods. Systematic literature searches were made to identify instruments, using predefined criteria relating to reliability, validity, responsiveness and precision. Results. Twelve AS-specific and three arthritis-specific instruments met the inclusion criteria. Three AS-specific instruments that measure health-related quality of life (HRQL) were reviewed. The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), the Bath Ankylosing Spondylitis Functional Index (BASFI) and the Dougados Functional Index (DFI) had the greatest amount of evidence for reliability, validity and responsiveness across a range of settings. Four instruments lacked evidence for test-retest or internal consistency reliability. Most were assessed for validity through comparisons with other instruments, global judgements of health, mobility or clinical and sociodemographic variables. Most were assessed for responsiveness through mean score changes. Three instruments lacked evidence of responsiveness. Conclusion. This review provides a contribution to AS assessment. AS-specific multi-item measures specific to the assessment of pain, stiffness, fatigue and global health were not identified; where assessed, these domains were largely measured with single-item visual analogue scales. Single items may provide a limited reflection of these important domains. The BASFI and DFI remain the instruments of choice for functional assessment. HRQL is recommended as a core assessment domain. Further concurrent evaluation is recommended.