Corticospinal tract integrity measured using transcranial magnetic stimulation and magnetic resonance imaging in neuromyelitis optica and multiple sclerosis

Background:Both multiple sclerosis (MS) and neuromyelitis optica (NMO) can present with transverse myelitis; however, NMO symptoms are usually more severe and may present with more extensive axonal loss. Transcranial magnetic stimulation (TMS)-based input–output recruitment curves can quantitatively assess the excitability of corticospinal tract pathways and myelin water imaging can quantify the amount of myelin within this same pathway.Objective:To compare differential effects of MS and NMO on TMS recruitment curves and myelin water imaging.Methods:Ten healthy controls, 10 individuals with MS and 10 individuals with NMO completed clinical assessments, a TMS assessment and magnetic resonance imaging scan to measure recruitment curves and myelin water fraction in the corticospinal tract.Results:Individuals with NMO had lower recruitment curve slopes (mean 13.6±6 μV/%) than MS (23.6±11 μV/%) and controls (21.9±9 μV/%, analysis of variance (ANOVA) P=0.05). Corticospinal tract myelin water fraction was lower ...