What's special about task in dystonia? A voxel-based morphometry and diffusion weighted imaging study

Abstract

Numerous brain imaging studies have demonstrated structural changes in the basal ganglia, thalamus, sensorimotor cortex, and cerebellum across different forms of primary dystonia. However, our understanding of brain abnormalities contributing to the clinically well-described phenomenon of task specificity in dystonia remained limited. We used high-resolution magnetic resonance imaging (MRI) with voxel-based morphometry and diffusion weighted imaging with tract-based spatial statistics of fractional anisotropy to examine gray and white matter organization in two task-specific dystonia forms, writer's cramp and laryngeal dystonia, and two non-task-specific dystonia forms, cervical dystonia and blepharospasm. A direct comparison between both dystonia forms indicated that characteristic gray matter volumetric changes in task-specific dystonia involve the brain regions responsible for sensorimotor control during writing and speaking, such as primary somatosensory cortex, middle frontal gyrus, superior/inferior temporal gyrus, middle/posterior cingulate cortex, and occipital cortex as well as the striatum and cerebellum (lobules VI-VIIa). These gray matter changes were accompanied by white matter abnormalities in the premotor cortex, middle/inferior frontal gyrus, genu of the corpus callosum, anterior limb/genu of the internal capsule, and putamen. Conversely, gray matter volumetric changes in the non-task-specific group were limited to the left cerebellum (lobule VIIa) only, whereas white matter alterations were found to underlie the primary sensorimotor cortex, inferior parietal lobule, and middle cingulate gyrus. Distinct microstructural patterns in task-specific and non-task-specific dystonias may represent neuroimaging markers and provide evidence that these two dystonia subclasses likely follow divergent pathophysiological mechanisms precipitated by different triggers.

Keywords: brain imaging; focal dystonia; task specificity.

Figure 1. Gray matter volumetric abnormalities in TSD and NTSD

(A) Results of initial analysis of variance (ANOVA) comparing gray matter volume (GMV) between TSD, NTSD and healthy controls. (B) GMV differences between NTSD patients and healthy controls. (C) GMV differences between TSD patients and healthy controls. (D) Direct comparison of GMV differences between TSD and NTSD groups. (E) Significant inverse correlation between GMV (in liters) in the right premotor cortex and disorder duration (in years) in the TSD group. Brain abnormalities are shown on a series of axial, sagittal and coronal sections in the standard MNI space. The corresponding coordinates of peak changes are given in the Table 1. The color bars represent F score (A), t scores (B, C, D) and r_s score (E), respectively.

Figure 2. White matter abnormalities in TSD and NTSD

(A) Initial analysis of variance (ANOVA) comparing fractional anisotropy (FA) as a measure of white matter integrity and coherence between TSD, NTSD and healthy controls. (B) Abnormal FA in the NTSD group compared to healthy subjects. (C) Abnormal FA in the TSD group compared to healthy subjects. (D) Differences in FA between TSD and NTSD groups. Brain abnormalities are shown on a series of axial, sagittal and coronal sections in the standard MNI space. The corresponding coordinates of peak changes are given in the Table 2. The color bars represent F score (A) and t scores (B, C, D), respectively.