Extensive and Strong Increase of Radial Diffusivity in Human Hypomyelinating Disorders

Marjan Steenweg¹, Nicole Wolf¹, Frederik Barkhof², Marjo van der Knaap¹, Petra Pouwels³

DTI-TBSS analysis of 25 patients with hypomyelinating disorders showed significantly reduced FA compared to 44 controls in almost the whole WM skeleton. This was co-localized with the extensive and large increase of radial diffusivity RD, while axial diffusivity AD was increased to a much smaller extent. In areas without change in AD the observed decrease in FA and increase in MD were only due to the increase in RD. These results strongly support the relationship between RD and myelin density also in humans, since histopathology in hypomyelinating disorders have shown severely impaired myelination, while axons are relatively well preserved.