Fig. 2.

DT MRI measures of the CST and motor callosal tracts. Mean FA and MD values of the CST bilaterally and motor callosal tracts are plotted per study group (healthy controls and patients with ALS, PUMN and ALS-mimic disorders). The dashed horizontal line indicates the mean value minus 2 standard deviations of the healthy control group. MD values are in × 10^− 3 mm² s^− 1. *p < 0.05, **p < 0.001 (ANOVA model followed by pair-wise comparisons, false-discovery rate-corrected for multiple comparisons and adjusted for subject's age). Abbreviations: ALS = amyotrophic lateral sclerosis; CC-precentral = callosal fibers linking the primary motor cortices; CC-SMA = callosal fibers linking the supplementary motor areas; CST = corticospinal tract; FA = fractional anisotropy; HC = healthy controls; MD = mean diffusivity; PUMN = predominantly upper motor neuron.