ORIGINAL RESEARCH Diffusion Tensor Imaging in the Assessment of Normal-Appearing Brain Tissue Damage in

BACKGROUND AND PURPOSE: Normal-appearing brain tissue (NABT) damage was established in multiple sclerosis by histology, MR spectroscopy, magnetization transfer imaging and diffusion tensor imaging (DTI). However, whether this phenomenon can be detected in relapsing neuromyelitis optica (RNMO) remains unclear. The aim of this study was to use DTI to investigate the presence of NABT damage in RNMO patients and its possible mechanism. METHODS: Conventional MR imaging and DTI scans were performed in 16 patients with RNMO without visible lesions on brain MR imaging and in 16 sex- and age-matched healthy control subjects. Histogram analysis of mean diffusivity (MD) and fractional anisotropy (FA) was performed in entire brain tissue (BT), white matter (WM), and gray matter (GM). Region of interest (ROI) analysis of MD and FA was also performed in WM regions being the continuation of the spinal white matter tracts or optic nerve (including medulla oblongata, cerebral peduncle, internal capsule and optic radiation), in corpus callosum without direct connection with them, and in some GM regions. RESULTS: From histogram analysis, we found that RNMO group had a higher average MD of the BT, WM and GM, a lower average MD peak height and a higher average MD peak location of the GM, and a higher average FA peak height of the WM than did control group. From region of interest analysis