But what sort of tired? Measuring fatigue in MS

<h3>Background</h3> Since 2019 the UK MS Register (UKMSR) has captured longitudinal patient reported outcomes in people with MS (pwMS). The Fatigue Severity Scale (FSS), a generic fatigue instrument, was selected as the UKMSR fatigue standard. A 2018 sub-study implemented the PROMIS-FATIGUE-MS-8a (PFS), an MS-specific fatigue outcome. <h3>Aim</h3> Characterise pwMS based on PFS level of fatigue. <h3>Method</h3> We identified 370 pwMS that completed four PFS, FSS and MSIS29v2 outcomes between 2021–2023, Using t-scores derived from PFS we grouped respondents at baseline into; no- fatigue (&lt;16, n=65), fatigue (≥16 &lt;26, n=130) and very fatigued (≥26, n=175). <h3>Results</h3> No-fatigue (mean-age 59.1, mean-onset-age 37.9, 64.6% RRMS), fatigue (mean-age 61.1, mean-onset-age 37.0, 45.4% RRMS) and very fatigued (mean-age 61.3, mean-onset-age 35.5, 37.7% RRMS) had stable fatigue over time in FSS and PFS with minor deviations. The most fatigued group were 1.5 standard deviations above the mean T-score. Normalised MSIS-29- Phys scores varied between no-fatigue (19.4), fatigued (41.2), and very fatigued (62.5). <h3>Discussion</h3> PFS is a valid metric for assessing MS fatigue in a UK population, there is a relationship between amount of disability and persistent fatigue. The most fatigued group were more than 1.5 standard deviations above mean with higher disability at all times.