Objective: To compare spinal cord diffusion tensor imaging (DTI) between multiple sclerosis (MS) and neuromyelitis optica (NMO) subjects with a remote clinical episode of transverse myelitis (TM). Background: NMO is a relapsing neurologic disease similar to MS. NMO is associated with greater sustained disability, likely related to greater tissue destruction in the spinal cord. Methods: This case-control study examined 10 healthy controls (HC), 10 MS and 10 NMO subjects. All MS and NMO subjects were greater than 12 months from a clinical episode of TM. Subjects underwent spinal cord DTI (25 direction encoding) at 3T with a reduced field of view EPI sequence. Regions of interest (ROIs) included posterior column and lateral corticospinal white matter tracts, central gray matter regions and the entire axial cross-section of the cord. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) were compared between groups by linear mixed modeling. Disability was measured using the Expanded Disability Status Scale (EDSS) for correlation with DTI parameters by Kendall’s tau. Results: Median EDSS was slightly higher in NMO compared to MS (3.5 vs. 2.0). Within T2 affected white matter lesions, RD was increased in both MS and NMO compared to HC (p<0.001, respectively) and to a greater extent in NMO than MS (p<0.001). Conversely, AD was decreased in both MS (p=0.001) and NMO (p<0.001). Overall, MD was increased in both MS (p=0.001) and NMO (p<0.001). NMO displayed decreased FA compared to MS (p=0.002) and HC (p<0.001). When controlling for EDSS, statistical significance remained for all findings. Both FA and RD distinguished regions affected by T2 lesion from areas upstream and downstream of T2 lesions (p<0.001). Increased gray matter MD, but not decreased gray matter FA, was observed in both MS and NMO compared to HC. EDSS correlated with whole cord mean RD (tau=0.43, p=0.012), inversely with FA (tau=-0.47, p=0.006), but did not correlate with AD (tau=-0.10, p=0.567) or MD (tau=0.34, p=0.050). Discussion/Relevance: In subjects with a remote history of TM, spinal cord DTI distinguished NMO from MS even when controlling for disability, indicating greater tissue destruction in NMO. Differences between groups were greater in white matter than gray matter. Unaffected white matter regions upstream and downstream from lesions also showed DTI abnormalities. Spinal cord DTI parameters correlated with disability in these subjects.
Read More: Diffusion tensor imaging distinguishes multiple sclerosis from neuromyelitis optica