Background and purpose: Diffusion tensor imaging (DTI) was used as a noninvasive method to evaluate the anatomy of the corticospinal tract (CST) and the pattern of its degeneration in amyotrophic lateral sclerosis (ALS).
Methods: Fourteen patients with ALS and 15 healthy controls underwent DTI. Parameters reflecting coherence of diffusion (fractional anisotropy, FA), bulk diffusion (apparent diffusion coefficient, ADC), and directionality of diffusion (eigenvalues) parallel to (lambda( parallel)) or perpendicular to (lambda( perpendicular)) fiber tracts were measured along the intracranial course of the CST.
Results: FA and lambda( parallel) increased, and ADC and lambda( perpendicular) decreased progressively from the corona radiata to the cerebral peduncle in all subjects. The most abnormal finding in patients with ALS was reduced FA in the cerebral peduncle contralateral to the side of the body with the most severe upper motor neuron signs. lambda( parallel) was increased in the corona radiata. Internal capsule FA correlated positively with symptom duration, and cerebral peduncle ADC positively with the Ashworth spasticity score.
Conclusion: There is a spatial dependency of diffusion parameters along the CST in healthy individuals. Evidence of intracranial CST degeneration in ALS was found with distinct diffusion changes in the rostral and caudal regions.