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


METHODS
Axial and radial diffusivity of the whole-brain WM were evaluated in 14 patients with FRDA and 14 healthy volunteers using DTI at 1.5 T and the tract-based spatial statistics (TBSS) method, part of FSL software.


RESULTS
TBSS analysis showed a single area in the central midbrain corresponding to the decussation of the SCPs which exhibited lower FA in patients than in controls. In this area, a significant increase of both axial and radial diffusivity was observed. No clusters of significantly decreased axial diffusivity were observed, while additional clusters of increase of radial diffusivity were present throughout the brain.


CONCLUSIONS
The selective decrease of FA in SCPs of FRDA patients reflecting chronic WM tract damage is associated with increase of both the axial and radial diffusivity, the latter more pronounced than the former. The ultrastructural and biophysical bases of the increased axial diffusivity in chronically degenerating WM tracts deserve further studies.
S. Giuseppe Hospital, Radiodiagnostic Section, Empoli, Italy.
Riccardo
R
Della Nave
Andrea
A
Ginestroni
Stefano
S
Diciotti
Elena
E
Salvatore
Andrea
A
Soricelli
Mario
M
Mascalchi
D000328:Adult; D016880:Anisotropy; D001921:Brain / Q000473:pathology; D016022:Case-Control Studies; D002531:Cerebellum / Q000473:pathology*; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D005621:Friedreich Ataxia / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D009410:Nerve Degeneration / Q000473:pathology*