Neural correlates of fatigue in multiple sclerosis: a combined neurophysiological and neuroimaging approach (R1)

Abstract

The present study is aimed at further exploring structural and functional correlates of fatigue in Relapsing- Remitting Multiple Sclerosis (RRMS) patients by using a combined approach by means of transcranial magnetic stimulation (TMS) and a Diffusion Tensor Imaging (DTI). The physiopathology of fatigue in MS is still poorly understood, although a variety of pathogenic mechanisms has been proposed. Our working hypothesis is that diffuse microstructural white matter damage may subtend the cortico-subcortical functional disconnection described in patients with MS and fatigue. We enrolled 30 RRMS patients (mean age 39±13; age range 24-63 years) with mild neurological impairment Expanded Disability Status Scale <3.5, divided into two groups on the basis of their fatigue severity scale (FSS) scoring (cutoff ≥ 4). All the patients underwent a neurological evaluation, a brain MRI acquisition (including DTI study) and a neurophysiological assessment by means of TMS in a pre-movement facilitation paradigm. Our data showed a significant mean diffusivity (MD) increase (p=0.036) in left thalamo-frontal reconstructions in the MS patients with fatigue compared to those classified as non-fatigued. Moreover, significant correlations were observed between FSS scale and MD as well as planar coefficient (CP) values extracted from frontal-thalamic connections bilaterally. Instead, the pre-movement facilitation showed a significant difference between the groups with particular regard to the Reaction Time- MEP50ms amplitude (p=0.03). Our work confirms that fatigue is associated with a disruption of brain networks involved in motor preparation processes, depending on several frontal-thalamic pathways. Such findings can have an important role when dealing with fatigue management in MS patients and could be eventually used as prognostic marker of MS course.