Combined structural and neurochemical evaluation of the corticospinal tract in amyotrophic lateral sclerosis

Our objective was to characterize the structural and metabolic changes of the corticospinal tract (CST) in ALS patients using combined diffusion tensor imaging (DTI) and magnetic resonance spectroscopic imaging (MRSI). Fourteen patients (male:female, 6:8; mean age, 54 years) and 14 controls (male:female, 8:6; mean age, 53 years) underwent imaging. Four regions of the CST were evaluated: precentral gyrus, corona radiata, posterior limb of the internal capsule, and cerebral peduncle. DTI and MRSI indices tested included fractional anisotropy (FA), apparent diffusion coefficient (ADC), and the ratio of N-acetylaspartate to choline (NAA/Cho) and creatine (NAA/Cr). In the precentral gyrus, NAA/Cho was reduced 18% (p < 0.001), NAA/Cr was reduced 9% (p=0.01), and FA was reduced 3% (p=0.02). NAA/Cho and NAA/Cr were reduced in the corona radiata (p < 0.001). Reduced NAA/Cho in the precentral gyrus correlated with shorter symptom duration (r=0.66, p=0.02) and faster disease progression (r=-0.65, p=0.008). Increased spasticity correlated with higher ADC in the precentral gyrus (R=0.52, p=0.005). In conclusion, both MRSI and DTI provided in vivo evidence of intracranial degeneration of the CST in ALS that was most prominent rostrally in the precentral gyrus.