Decreased fractional anisotropy (FA) demonstrated by diffusion tensor MR imaging (DTI) in areas of white matter (WM) damage is generally associated with increase of radial diffusivity, while axial diffusivity is reported to be decreased, unchanged, or increased. Aiming to better define the type of axial diffusivity change occurring in a typical human neurodegenerative disease, we investigated axial and radial diffusivity in Friedreich's ataxia (FRDA) which is characterized by selective neuronal loss of the dentate nuclei and atrophy and decreased FA of the superior cerebellar peduncles (SCPs).

Axial diffusivity is increased in the degenerating superior cerebellar peduncles of Friedreich's ataxia