Weekly diffusion-weighted imaging of normal-appearing white matter in MS.

To elucidate the dynamics and the nature of normal-appearing white matter (NAWM) changes preceding new lesion formation in MS, the authors obtained weekly diffusion-weighted images for 12 weeks from 6 patients. NAWM areas subsequently involved by enhancement had a significant increase in mean diffusivity values starting 6 weeks before the appearance of enhancement (p values ranging between < 0.0001 and 0.04). This suggests that focal edema and demyelination play a part in the NAWM changes preceding new lesion formation in MS.