Decreased grey matter in the postural control network is associated with lateral flexion of the trunk in Parkinson's disease

Abstract

Background: Disruption of central networks, particularly of those responsible for integrating multimodal afferents in a spatial reference frame, were proposed in the pathophysiology of lateral trunk flexion in Parkinson's disease (PD). Knowledge about the underlying neuroanatomical structures is limited.

Objective: To investigate if decreased focal grey matter (GM) is associated with trunk flexion to the side and if the revealed GM clusters correlate with a disturbed perception of verticality in PD.

Methods: 37 PD patients with and without lateral trunk flexion were recruited. Standardized photos were taken from each patient and trunk orientation was measured by a blinded rater. Voxel-based morphometry (VBM) was used to detect associated clusters of decreased GM. The subjective visual vertical (SVV) was assessed as a marker for perception of verticality and SVV estimates were correlated with GM clusters.

Results: VBM revealed clusters of decreased GM in the right posterior parietal cortex and in the right thalamus were associated with lateral trunk flexion. The SVV correlated with the extent of trunk flexion, and the side of the SVV tilt correlated with the side of trunk flexion. GM values from the thalamus correlated with the SVV estimates.

Conclusions: We report an association between neurodegenerative changes within the posterior parietal cortex and the thalamus and lateral trunk flexion in PD. These brain structures are part of a network proposed to be engaged in postural control and spatial self-perception. Disturbed perception of verticality points to a shifted egocentric spatial reference as an important pathophysiological feature.

Keywords: Lateral trunk flexion; MRI; Parkinson’s disease; Pisa syndrome; Subjective visual vertical.

Fig. 1

Illustration of the trunk measurement in the sitting and standing position.

Fig. 2

Clusters of decreased grey matter associated with lateral flexion of the trunk in PD. Multiple axial slices of a T2-weighted MRI scan of the brain with their respective z-coordinates are shown. The clusters (cluster-forming threshold p < 0.001, FWE correction at the cluster-level) that correlated with lateral flexion of the trunk in our voxel-based morphometry model are superimposed in red. The lower row of slices shows the results from the approach in which scans from patients leaning to the left were right-left flipped (#). A color bar with the coding of the p-values (1-p) is provided at the bottom of the figures. Abbreviations: AnG – angular gyrus; IPL – inferior lobule; IPS – intraparietal sulcus; PPC – posterior parietal cortex; TPC – temporoparietal cortex. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)