Diffusion Tensor Imaging of Vascular Parkinsonism:  Structural Changes in Cerebral White Matter and the Association With Clinical Severity

Figure 1. Demonstration of selected fiber tract involvement on a standard brain T1-weighted magnetic resonance imaging template. Red (arrow 1) indicates tracts passing through the genu of the corpus callosum; yellow (arrow 2), tracts from the frontal lobe passing through the anterior limb of the internal capsule; orange (arrow 3), tracts from the premotor area to the brainstem (premotor); green (arrow 4), tracts from the motor cortex to the brainstem (pyramidal); cyan (arrow 5), arcuate fasciculus; blue (arrow 6), tracts from the supplementary motor area to the brainstem; purple (arrow 7), superior longitudinal fasciculus; deep sky blue (arrow 8), tracts passing through the splenium of the corpus callosum.

Figure 2. Maps showing significant intergroup differences in fractional anisotropy (FA) and mean diffusivity (MD). A, Voxel-based significance maps of the decreased FA in patients with vascular parkinsonism (VP), as computed by statistical parametric mapping (SPM) t tests. The color scale represents the t value significance for the FA decreases. B, Voxel-based significance maps of the increased MD in VP patients, as computed by SPM t tests. The color scale represents the t value significance for the MD increases. The number indicates the z -axis coordinate in the Montreal Neurological Institute space (given in millimeters). L indicates left side; R, right side.

Figure 3. Correlation between the Unified Parkinson's Disease Rating Scale modified postural instability gait difficulty (PIGD) scores and diffusion tensor imaging variables for regions with significant group difference. A, Mean fractional anisotropy (FA) values (0.42 + 7.13 × 10⁻⁴ × age − 0.16 × modified PIGD score part III) from significantly lower FA regions in vascular parkinsonism (VP) vs the modified PIGD score part III (P = .001; adjusted R² = 0.77). B, Mean FA values (0.45 + 6.80 × 10⁻⁴ × age + 0.012 × modified PIGD score parts II and III) from significantly lower FA regions in VP vs the modified PIGD scores parts II and III (P = .009; adjusted R² = 0.65). C, Mean mean diffusivity (MD) values (82.3 × 10⁻⁵ − 6.3 × 10⁻⁷ × age + 0.17 × 10⁻⁵ × modified PIGD score part III) from significantly higher MD regions in VP vs the modified PIGD score part III (P = .04; adjusted R² = 0.51). D, Mean MD values (73.4 × 10⁻⁵ − 4.1 × 10⁻⁷ × age + 1.4 × 10⁻⁵ × modified PIGD score parts II and III) from significantly higher MD regions in VP vs the score derived from modified PIGD scores parts II and III (P = .03; adjusted R² = 0.55).

Figure 4. Correlation between the Unified Parkinson's Disease Rating Scale modified postural instability gait difficulty (PIGD) scores and diffusion tensor imaging variables for specific white matter fiber bundles. A, Mean fractional anisotropy (FA) of the tracts from the frontal lobe passing through the anterior limb of the internal capsule (0.55 + 0.0015 × age − 0.015 × modified PIGD score part III) vs the modified PIGD score part III (P = .02; R² = 0.59). B, Mean FA of the tracts from the frontal lobe passing through the anterior limb of internal capsule (0.59 + 0.0015 × age − 0.011 × modified PIGD score parts II and III) vs the modified PIGD score parts II and III (P = .03; R² = 0.54). C, Mean mean diffusivity values of the tracts that pass through the genu of the corpus callosum (59.9 × 10⁻⁵ + 1.83 × 10⁻⁶ × age + 5.05 × 10⁻⁵ × modified PIGD score part III) vs the modified PIGD score part III (P = .01; R² = 0.61).