Quality and acceptability of patient-reported outcome measures used to assess fatigue in axial spondyloarthritis (axSpA): a systematic review (protocol)

Axial spondyloarthritis (axSpA) is an inflammatory disease that primarily affects the spine and pelvis, impairing mobility to the detriment of the patient’s physical wellbeing [1]. It is characterised by widespread back and joint pain and stiffness [2]. axSpA and ankylosing spondylitis (AS) are two facets of a single disease distinguished by whether radiographic sacroiliitis is observable by X-ray examination (AS) or not (axSpA) [2]. Up to 75% of axSpA patients report experiencing fatigue [3‐7], and for many, this is both severe and frequent [7]. Patients with AS have highlighted the relative importance of seeking to better understand the fatigue associated with their illness [8], underlining the need for an appropriate fatigue assessment that really captures what matters to patients. As exemplified in rheumatoid arthritis (RA), a review of methods of fatigue assessment [9] and qualitative research with patients highlighted both the multi-faceted nature of RA fatigue [10] and the inadequacy of current methods of assessment. The result was the development of a patient-reported outcome measure (PROM) specific to RA fatigue—the Bristol Rheumatoid Arthritis Fatigue Multidimensional Questionnaire (BRAF-MDQ) [11, 12]. PROMs are single- or multi-item questionnaires which seek to provide a patient-derived assessment of how they feel, what they can and cannot do and how well they are living their lives as a consequence of their health and associated health care [13].

Current assessment guidance for AS exists in the form of a core outcome set (COS) [14]. The COS provides guidance for the minimum number of outcomes to include in future clinical practice and clinical trials: that is, pain, stiffness, function, global wellbeing and spinal mobility [14, 15]. A recent update recommends the assessment of fatigue severity with a single-item visual analogue scale (VAS) [16]. However, evidence from a large UK cohort of AS patients highlighted significant limitations with a single-item assessment of fatigue, including the failure to identify some patients with major fatigue, to detect important change in fatigue, to reflect the multi-dimensional nature of fatigue or to detail the nuances of fatigue essential to driving tailored healthcare.

A growing number of multi-item fatigue-specific (for example, the Multidimensional Fatigue Inventory (MFI-20) [17] and Fatigue Severity Scale [18]) and condition-fatigue-specific (for example, the BRAF-MDQ [12] and Functional Assessment of Cancer Therapy scale [19]) PROMs are now available. This growth in availability reflects the importance of capturing the multi-faceted, often condition-specific, nature of fatigue [20] and the importance of seeking to reflect the outcomes that really matter to patients [21]. However, it is unclear how well these measures perform in the axSpA population; it cannot be assumed that the measurement and practical properties of measures are consistent across different patient populations. Confidence in the use of PROM-based assessment is underpinned by evidence of performance in the population of interest [22], and structured reviews of PROM quality and acceptability provide essential evidence to inform selection.

The proposed systematic review will evaluate the quality (measurement properties), relevance (measures what is important) and acceptability (simplicity and convenience) of clearly defined and reproducible multi- and single-item PROMs which purport to measure fatigue and have been completed by the axSpA population. A short list of ‘best’ measures of fatigue for use with the axSpA population will be developed to inform recommendations for use in both routine clinical practice and research.

The review will include published studies reporting evidence of the development, measurement and/or practical properties of clearly defined and reproducible measures of fatigue evaluated following completion by patients with axSpA. The review will be completed and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [23].

Study methodological quality will be assessed against the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) guidelines [24, 25]. The measurement and/or practical properties of included measures will be assessed against a transparent appraisal framework informed by current international standards for PROM quality [22, 26‐29].

Awareness of the importance of fatigue in inflammatory conditions has grown over the past decade [20]. Whilst patients report fatigue as one of the key symptoms of their condition, there is limited evidence of an improved understanding of fatigue in axSpA and its impact on patients’ lives [3, 38, 39]. Moreover, growing evidence suggests that the experience of fatigue is not homogeneous across conditions [10, 40] and hence a generic approach to assessment may miss important aspects of fatigue for particular patient groups.

This study will provide the first robust and transparent evaluation of patient-reported measures of fatigue used in the axSpA population, synthesising evidence of quality, relevance and acceptability. The findings of this review will inform the selection of patient-reported fatigue assessment, thus impacting future research which seeks to better understand the nature of axSpA fatigue. Improving the assessment of fatigue in routine practice, service evaluation and research will enhance our understanding of the way in which fatigue impacts upon the lives of people with axSpA, and the way in which their fatigue responds to fatigue-management strategies.