Pyramidal tract lesions and movement-associated cortical recruitment in patients with MS

Cortical functional changes, with the potential to limit the functional consequences of tissue injury, have been shown in patients with multiple sclerosis (MS). In this study, we assessed the influence of MS-related tissue damage of the brain portion of the left pyramidal tract on the corresponding movement-associated patterns of cortical recruitment in a large sample of MS patients when performing a simple motor task with their fully normal functioning right upper limbs. We investigated 76 right-handed patients with definite MS. In each subject, functional magnetic resonance imaging (fMRI) was acquired during the performance of a simple motor task with the dominant, right upper limb. During the same session, dual-echo, magnetization transfer (MT) and diffusion tensor (DT) MRI sequences were also obtained to quantify the extent and the severity of pyramidal tract damage. Lesions along the left pyramidal tract were identified in 43 patients. Compared to patients without pyramidal tract lesions, patients with such lesions had more significant activations of the contralateral primary sensorimotor cortex (SMC), secondary sensorimotor cortex (SII), inferior central sulcus, and cingulate motor area (CMA). They also showed more significant activations of several regions of the ipsilateral hemisphere, including the primary SMC and the precuneus. In these patients, T2 lesion load of left pyramidal tract was correlated with the extent of activation of the contralateral primary SMC (r2 = 0.25, P < 0.0001), whereas no correlations were found between the extent of fMRI activations and the severity of intrinsic lesion damage, as well as with left pyramidal tract normal-appearing white matter damage. This study shows that, in patients with MS, following injury of the motor pathways, there is an increased recruitment of a widespread sensorimotor network, which is likely to contribute to limit the appearance of overt clinical deficits.