Increased radial diffusivity in spinal cord lesions in neuromyelitis optica compared with multiple sclerosis

Background: Multiple sclerosis (MS) and neuromyelitis optica (NMO) both affect spinal cord with notable differences in pathology. Objective: Determine the utility of diffusion tensor imaging (DTI) to differentiate the spinal cord lesions of NMO from MS within and outside T2 lesions. Methods: Subjects greater than or equal to 12 months from a clinical episode of transverse myelitis underwent a novel transaxial cervical spinal cord DTI sequence. Ten subjects with NMO, 10 with MS and 10 healthy controls were included. Results: Within T2 affected white matter regions, radial diffusivity was increased in both NMO and MS compared with healthy controls (p<0.001, respectively), and to a greater extent in NMO than MS (p<0.001). Axial diffusivity was decreased in T2 lesions in both NMO and MS compared with controls (p<0.001, p=0.001), but did not differ between the two diseases. Radial diffusivity and fractional anisotropy within white matter regions upstream and downstream of T2 lesions were different from controls in each disease. Conclusions: Higher radial diffusivity within spinal cord white matter tracts derived from diffusion tensor imaging were appreciated in NMO compared with MS, consistent with the known greater tissue destruction seen in NMO. DTI also detected tissue alterations outside T2 lesions and may be a surrogate of anterograde and retrograde degeneration.