Perceived physical and mental fatigability in older adults with and without multiple sclerosis

Background: Fatigue stands out as a prevalent and debilitating symptom in both Multiple Sclerosis (MS) and the aging population. Traditional methods for measuring perceived fatigue may not adequately account for individual activity differences, leading to varied prevalence rates. Perceived fatigability anchors fatigue to specific activities with predetermined intensity and duration, thereby mitigating self-pacing bias. Despite its potential, perceived fatigability is poorly understood in older adults, particularly those with neurological conditions, including MS. This study thus aimed to (1) investigate whether, among older adults, MS was associated with worse perceived physical and mental fatigability; (2) evaluate whether, among older adults with MS (OAMS), greater patient-reported disease-related disability was associated with worse perceived physical and mental fatigability. Methods: Participants were 96 older adults with a physician-confirmed diagnosis of MS (mean age: 64.6 +/- 4.2) and 110 healthy controls (mean age: 68.2 +/- 7.2), all confirmed to be dementia-free through established case conference procedures. Physical and mental fatigability were measured using the Pittsburgh Fatigability Scale, a 10-item questionnaire (score range: 0 to 50) designed to assess fatigue levels that individuals expect to feel after engaging in a range of typical activities for older adults. MS disease-related disability was assessed with the Patient Determined Disease Steps scale, which ranges from 0 (normal) to 8 (bedridden), with scores >= 2 indicating worse MS-related disability after a median split. Separate linear regression models were performed to investigate associations between group status (MS vs. Control) as the predictor and perceived physical and mental fatigability scores as the outcome variables. Within the MS group, additional linear regression models were performed to explore the relationship between disease-related disability and fatigability levels. All models adjusted for age, sex, race, education, global health, general cognitive function, and depressive symptoms levels. Results: The fully adjusted models yielded the following key findings: OAMS reported significantly higher levels of perceived physical fatigability (M = 25.11 +/- 9.67) compared to controls (M = 17.95 +/- 8.35) (p = 0.003). Similarly, the perceived mental fatigability in OAMS (M = 16.82 +/- 11.79) was significantly greater than that in controls (M = 9.15 +/- 7.12) (p = 0.003). Within the MS group, individuals with greater disease-related disability reported significantly greater levels of both physical (M = 30.13 +/- 7.71 vs. 18.67 +/- 8.00, p < 0.001) and mental fatigability (M = 20.31 +/- 12.18 vs. 12.33 +/- 9.69, p = 0.009) compared to those with lower MS-related disability. Of note, the significance of these findings persisted in models that adjusted for depressive symptoms. Conclusion: Our study provides compelling evidence that OAMS exhibit significantly higher perceived physical and mental fatigability compared to healthy controls. Additionally, worse MS-related disability correlates with worse physical and mental fatigability. These results persist after adjusting for confounders including depressive symptoms. Our findings underscore the necessity of holistic management strategies that cater to both physical and psychological aspects of MS, laying a foundation for future studies to uncover the pathophysiological mechanisms of fatigability in older adults with and without MS.