Assessing fatigue in adults with axial spondyloarthritis: a systematic review of the quality and acceptability of patient-reported outcome measures

Objective. The aim was to evaluate the quality and acceptability of patient-reported outcome measures used to assess fatigue in patients with axial spondyloarthritis. Methods. A two-stage systematic review of major electronic databases (1980-2017) was carried out to: (i) identify measures; and (ii) identify evaluative studies. Study and measurement quality were evaluated following international standards. Measurement content was appraised against a conceptual model of RA-fatigue. Results. From 387 reviewed abstracts, 23 articles provided evidence for nine fatigue-specific measures: 6 multi-item and 3 single-item. No axial spondyloarthritis-fatigue-specific measure was identified. Evidence of reliability was limited, but acceptable for the Multi-dimensional Fatigue Inventory (internal consistency, test-retest) and Short Form 36-item Health Survey Vitality subscale (SF-36 VT; internal consistency). Evidence of construct validity was moderate for the Functional Assessment of Chronic Illness Therapy-Fatigue and 10 cm visual analog scale, limited for the SF-36 VT and not available for the remaining measures. Responsiveness was rarely evaluated. Evidence of measurement error, content validity or structural validity was not identified. Most measures provide a limited reflection of fatigue; the most comprehensive were the Multi-dimensional Assessment of Fatigue, Multi-dimensional Fatigue Inventory-20, Functional Assessment of Chronic Illness Therapy-fatigue and Fatigue Severity Scale. Conclusion. The limited content and often poor quality of the reviewed measures limit any clear recommendation for fatigue assessment in this population; assessments should be applied with caution until further robust evidence is established. Well-developed, patient-derived measures can provide essential evidence of the patient's perspective to inform clinical research and drive tailored health care. The collaborative engagement of key stakeholders must seek to ensure that future fatigue assessment is relevant, acceptable and of high quality.