Fatigue is common to all the rheumatic conditions, in varying degrees, and is a frequent, often severe problem that has major consequences on patients' lives (1–4). In response to these concerns, a body of research subsequently led to international consensus that fatigue must be evaluated in all clinical trials of rheumatoid arthritis and potentially all fibromyalgia syndrome trials (5, 6). The 12 fatigue patient-reported outcome measures (PROMs) reviewed in this section have been selected because they are currently or have recently been used in rheumatology populations. Fatigue PROMs in rheumatology were identified from previous reviews (7), then Medline, Cumulative Index to Nursing and Allied Health Literature, and PsycINFO searched for each PROM name plus each major rheumatologic condition. Not all articles could be evaluated and reported in this overview; therefore, those that evidenced strengths and weaknesses were included where possible. However, a full systematic review with meta-analysis would be welcome, as a limitation of this overview is that some articles contributing useful data may have been omitted. The fatigue PROMs are reviewed in alphabetical order. Three additional scales with fatigue components are reviewed elsewhere in this edition: the Bath Ankylosing Spondylitis Disease Activity Index in the Measures of Ankylosing Spondylitis article, the Fibromyalgia Impact Questionnaire in the Measures of Fibromyalgia article, and the Nottingham Health Profile in the Adult Measures of General Health and Health-Related Quality of Life article.
When selecting a fatigue PROM, researchers and clinicians should consider whether their needs are best served by a single-item PROM as a screening tool, by multi-item PROMs that explore broader fatigue issues to create a global score, or by multidimensional PROMs that produce subscale scores for a range of different facets or domains of fatigue (e.g., cognitive and physical fatigue). Multi-dimensional PROMs with subscales may be useful for informing or evaluating interventions or exploring fatigue causality. Some fatigue PROMs relate to severity only, while others include items of both severity and consequence or impact.
Fatigue PROMs should differentiate between rheumatology populations and healthy controls. Many studies have shown that association between fatigue PROMs and inflammatory markers is not strong, and that fatigue is likely to have multicausal pathways of clinical variables (e.g., pain, disability) and psychosocial variables (e.g., mood, beliefs) combined in varying amounts (1, 8–10). Fatigue PROMs should therefore show moderate correlation (r = 0.3–0.49) or large correlation (r = >0.5) with these variables (11). Very strong associations (e.g., >0.75) might be expected when examining criterion validity with other fatigue scales. Fatigue in rheumatologic conditions can be constant and persistent, but can also appear without warning as an overwhelming event (2–4). Reliability of fatigue PROMs can therefore be problematic to evaluate due to the fluctuating and unpredictable nature of fatigue itself. Some fatigue PROMs have therefore been tested for stability over several weeks, and some over a matter of hours, both attempting to capture patients during a stable episode. Test–retest correlations of ≥0.7 are considered acceptable (12). Evaluation data are presented for rheumatology populations, but where these could not be found, data are presented from the original condition in which the PROM was developed.