Dual Encoded MT and Diffusion Provides Microstructural Insight in ARSACS Disease

Motivation: ARSACS is a genetic disease characterized by spasticity and ataxia corresponding to involvement of the corticospinal tracts (CST) and cerebellum. Goal(s): Previous reports suggest that the abnormally enlarged transverse pontine fibers (TPF) compress the CST where they cross, causing their developmental impairment. Approach: To test this hypothesis, advanced techniques that combine diffusion and magnetization transfer imaging were used to glean tract-specific microstructural properties. Results: Results indicate lower fiber density and axon caliber in the CST compared to controls, but relatively unaffected TPF, suggesting that geometry and crossing fibers could have driven the DTI-based previous hypothesis. Impact: Our results obtained through advanced MR techniques are in contrast with the previous hypothesis that the TPF 'squeeze' the CST in ARSACS, thus causing their abnormal development. Our observations have a direct impact on the understanding of this disease.