Impact of lesion damages along the whole motor pathways on disability in multiple sclerosis

Abstract

International audienceIntroduction: The anatomical substrate of motor disability in MS patients is not fully understood. Studyingthe distribution of corticospinal tracts (CST) lesions per side, from the brain to the end of the thoracic spinal cord (SC) couldprovide a better association with patient motor deficits evaluated per limb.Objectives: i) To describe lesion preferential location along the CST; ii) To investigate the association between CST lesionsand motor functional consequences, as measured using the EDSS, and the ASIA motor scores and electrophysiology (Centralmotor conduction time (CMCT)) per limb.Methods: 21 relapsing remitting MS (median EDSS=2.5) and 9 progressive MS patients (median EDSS=5.2) with clinicalpyramidal symptoms were scanned on a 3T Siemens MRI scanner. White matter lesions were segmented on 3D FLAIR for thebrain, on T2* for cervical SC and T2 for thoracic SC. For each patient, registration to an atlas was computed using Anima andSCT toolboxes. Lesion volume fraction along the CST (defined as "lesion volume along the CST"/"overall CST volume") wascalculated separately for the both sides on 3 regions: brain including brainstem, C1 to C7 (C1C7) and T1 to T10 (T1T10).Finally, the relationships between lesion volume fraction and the associated lateralized disability scores were assessed usingmultiple linear models, adjusting for age and disease duration.Results: In MS patients, lesion volume fraction was higher in the C1C7 portion compared to the brain and T1T10 portion (allp’s.6; all p’s<.005). Finally, we observed a mild positive association betweenlesion volume fraction in T1T10 and CMCT for inferior limbs on the left side (std-beta=.53; p=.02).Conclusions: CST damage is not homogeneous along the tract and predominates in the cervical portion. It has clearconsequences on motor conduction velocities measured using electrophysiology. Future work will include an assessment oflesion severity to better explain lesion consequences on motor disability