Brain white matter diffusion tensor metrics from clinical 1.5T MRI distinguish between ALS phenotypes

Patients with amyotrophic lateral sclerosis (ALS) can present with varying degrees of upper motor neuron (UMN) and lower motor neuron dysfunction. Previous diffusion tensor imaging (DTI) studies, in which ALS patients were not separated by the degree of UMN dysfunction, have resulted in conflicting or inconclusive results. We hypothesized that (1) categorizing ALS patients by their clinical phenotype can reveal differences in DTI abnormalities along the corticospinal tract (CST), and (2) data obtained from routine clinical DTI scans can provide this type of information. Clinical DTI scans were obtained at 1.5T in 87 ALS patients (categorized into four subgroups based on clinical phenotype) and in 12 neurologic controls. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity values from the CST were compared between ALS subgroups and controls. Significantly reduced FA and elevated MD values were observed in ALS patients compared to controls at the subcortical motor cortex level. Significant differences in AD values were not only seen between control and ALS patients but also between the ALS subgroups, suggesting divergent pathologies in these ALS patients. Classifying ALS patients by phenotype reveals differences in CST abnormalities between subgroups and may provide novel insights into disease mechanisms. The close similarity of our results from routine clinical scans with published research studies suggests wider accessibility to useful DTI metrics.