Is fatigue associated with exercise tolerance among patients suffering from multiple sclerosis?

Valet, Maxime [UCL] Stoquart, Gaëtan [UCL] Glibert, Yumiko [UCL] Hakizimana, Jean-Claude [UCL] Lejeune, Thierry [UCL]

Objective: Fatigue is the most common and disabling symptom among patients suffering from Multiple Sclerosis (MS). Its underlying mechanisms are poorly understood. From the initial stages of the disease, a physical deconditioning is also observed among these patients. The aim of this study is to assess the cardiorespiratory endurance (i.e. exercise tolerance functions) and self-reported fatigue, as well as their associations, among patients suffering from MS with mild disability (Expanded Disability Status Scale ≤ 4), in order to progress in the comprehensive management of this symptom. Material and methods: Twenty one patients with MS (15 women; age: 26-64 years, median 46 years; duration of disease: 0.33-48 years, median 7.25 years; EDSS 0-4, median 2.5; clinical forms: Relapsing –Remitting: 16, Primary Progressive: 4, Secondary Progressive: 1) were evaluated. Cardiorespiratory endurance was assessed by a maximal exercise test on a cycle ergometer, from which different indices were extracted: VO2-max, Oxygen Uptake Efficiency Slope (OUES) at different points and Physical Working Capacity at 75% of maximal heart rate (PWC75%). The Timed Up-and-Go (TUG) test was performed to assess functional mobility. Perceived fatigue, anxiety and depression and quality of life were respectively assessed by the following questionnaires: Modified Fatigue Impact Scale (MFIS), Fatigue Severity Scale (FSS), Hospital Anxiety and Depression Scale (HADS) and Short Form Health Survey (SF-36v2). Results: The majority of the patients (n = 13, 62%) presented a pathological level of perceived fatigue, based on the FSS criterion (FSS>5). The cardiorespiratory endurance indices are decreased among the patients, compared with the normative values from the general population. Low-to-moderate negative correlations (p < 0.05) are observed between perceived fatigue and VO2-max (FSS: r = -0.59; MFIS: r = -0.43). The OUES is weakly correlated with the MFIS (r = -0.40). Functional mobility (TUG) is moderately correlated to exercise tolerance (VO2-max: r= -0.56) and fatigue (MFIS: r = 0.64). Discussion: Our data show that our patients are deconditioned and most have pathological level of fatigue. This fatigue is correlated to physical deconditioning. This suggests that improving exercise tolerance functions could help reducing fatigue and improving functional mobility among patients suffering from MS with mild neurological disability.