Functional magnetic resonance imaging correlates of fatigue in multiple sclerosis

Although fatigue is a common and troublesome symptom of multiple sclerosis (MS), its pathogenesis is poorly understood. In this study, we used functional magnetic resonance imaging (fMRI) to test whether a different pattern of movement-associated cortical and subcortical activations might contribute to the development of fatigue in patients with MS. We obtained fMRI during the execution of a simple motor task with completely normally functioning hands from 15 MS patients with fatigue (F), 14 MS patients without fatigue (NF), and 15 sex- and age-matched healthy volunteers. F and NF MS patients were also matched for major clinical and MRI variables. FMRI data were analyzed using statistical parametric mapping. In all patients, severity of fatigue was rated using the Fatigue Severity Scale (FSS). Compared to healthy subjects, MS patients showed more significant activations of the contralateral primary somatomotor cortex, the contralateral ascending limb of the Sylvian fissure, the contralateral intraparietal sulcus (IPS), the contralateral supplementary motor area, and the ipsilateral and contralateral cingulate motor area (CMA). Compared to F MS patients, NF patients showed more significant activations of the ipsilateral cerebellar hemisphere, the ipsilateral rolandic operculum, the ipsilateral precuneus, the contralateral thalamus, and the contralateral middle frontal gyrus. In contrast, F MS patients had a more significant activation of the contralateral CMA. Significant inverse correlations were found between FSS scores and relative activations of the contralateral IPS (r = -0.63), ipsilateral rolandic operculum (r = -0.61), and thalamus (r = -0.62). This study provides additional evidence that fatigue in MS is related to impaired interactions between functionally related cortical and subcortical areas. It also suggests that fMRI might be a valuable tool to monitor the efficacy of treatment aimed at reducing MS-related fatigue.