Utilizing Perceived Fatigability to Identify Cognitive and Mobility Impairments in Aging and Multiple Sclerosis.

BackgroundPerceived fatigability-subjective physical or mental energy depletion within specified activity contexts-is prevalent in aging and neurological conditions. Although the Pittsburgh Fatigability Scale (PFS) is validated for older adults and those with multiple sclerosis (OAMS), its subscale cut-offs and clinical relevance for cognitive and mobility outcomes have not been examined in neurologically affected aging populations.MethodsWe studied 224 older adults (≥60 years): 109 OAMS and 115 controls who completed the PFS, neuropsychological testing, the Short Physical Performance Battery (SPPB), and, for OAMS, the Patient Determined Disease Steps (PDDS). Receiver operating characteristic (ROC) analyses assessed PFS subscales' accuracy in discriminating MS, mild cognitive impairment (MCI), mobility impairment (SPPB ≤9), and worse MS-related disability (PDDS ≥2). Logistic regression adjusting for demographic and clinical covariates generated refined ROC curves and cut-offs.ResultsBoth PFS subscales demonstrated moderate accuracy (area under the curve 0.59-0.75) for discriminating MS, MCI, and mobility impairment when unadjusted, with accuracy often exceeding 0.80 after covariate adjustment. Among OAMS, mental fatigability more accurately identified MCI, whereas physical fatigability better detected worse MS-related disability. Cut-offs were higher in OAMS than in healthy controls, varying by subscale and clinical outcome. Adjusted analyses revealed nuances in cut-offs, with physical fatigability thresholds consistently higher than mental fatigability.ConclusionPFS subscales can identify MS, cognitive impairment, and mobility impairment in older adults. Cut-offs appear population- and outcome-specific, indicating that thresholds derived from healthy older cohorts may not apply directly to neurological populations. Covariate adjustment refines discriminative accuracy, potentially guiding need for further functional monitoring.