Studies of relapsing neuromyelitis optica (RNMO) using advanced MRI techniques are limited compared with those done on multiple sclerosis (MS). The present study used diffusion tensor imaging (DTI) to investigate whether occult brain damage exists in RNMO patients. DTI scans using a 3.0T MRI scanner were performed in 24 clinically confirmed RNMO patients whose conventional brain MRI results were normal, and also in 24 age- and sex-matched healthy control subjects. DTI data were processed to generate fractional anisotropy (FA) and mean diffusivity (MD) maps, and region of interest (ROI) analyses were performed to obtain these parameters in white matter (including medulla oblongata, cerebral peduncle, optic radiation, genu of corpus callosum, splenium of corpus callosum, and internal capsule) and gray matter (including thalamus and putamen). Regional measures from patients at stable and acute phases were compared with healthy controls. Both acute and stable NMO patients had a higher average FA in ROIs of the thalamus and putamen. Acute NMO patients had significantly higher average MDs than controls in the genu of corpus callosum and optic radiation, and significantly lower average MDs in the medulla oblongata. Stable NMO patients had increased MDs in the genu of corpus callosum and optic radiation, but lower MDs in the medulla oblongata, internal capsule and thalamus. The DTI findings confirm the presence of occult tissue damage in normal-appearance white and gray matter, especially deep gray matter, in RNMO patients. This study adds further to the evidence that DTI is suitable as a tool for characterizing subtle brain tissue damage.
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