Diffusion kurtosis and quantitative susceptibility mapping MRI are sensitive to structural abnormalities in amyotrophic lateral sclerosis

Objective: To construct a clinical diagnostic biomarker using state-of-the-art microstructural MRI in the motor cortex of people with amyotrophic lateral sclerosis (ALS). Methods: Clinical and MRI data were obtained from 21 ALS patients (aged 54 +/- 14 years, 33% female) and 63 age- and gender-matched controls (aged 48 +/- 18 years, 43% female). MRI was acquired at 3T and included T1weighted scan (for volumetrics), arterial spin labelling (for cerebral blood flow), susceptibility-weighted angiography (for iron deposition) and multiband diffusion kurtosis imaging (for tissue microstructure). Group differences in imaging measures in the motor cortex were tested by general linear model and relationships to clinical variables by linear regression. Results: The ALS group had mild-to-moderate impairment (disease duration: 1.8 +/- 0.8 years; ALS functional rating scale 40.2 +/- 6.0; forced vital capacity 83% +/- 22%). No age or gender differences were present between groups. We found significant group differences in diffusion kurtosis metrics (apparent, mean, radial and axial kurtosis: p < .01) and iron deposition in the motor cortex (p = .03). Within the ALS group, we found significant relationships between motor cortex volume, apparent diffusion and disease duration (adjusted R-2 = 0.27, p = .011); and between the apparent and radial kurtosis metrics and ALS functional rating scale (adjusted R-2 = 0.25, p = .033). A composite imaging biomarker comprising kurtosis and iron deposition measures yielded a maximal diagnostic accuracy of 83% (81% sensitivity, 85% specificity) and an area-under-the-curve of 0.86. Conclusion: Diffusion kurtosis is sensitive to early changes present in the motor region in ALS. We propose a composite imaging biomarker reflecting tissue microstructural changes in early ALS that may provide clinically valuable diagnostic information.