Cortical involvement of lateral trunk flexion and verticality misperception in Parkinson's disease

Lateral trunk flexion is a common form of postural abnormality in Parkinson's disease and could be associated with verticality misperception. However, the mechanisms underlying lateral trunk flexion and verticality misperception in Parkinson's disease remain unclear. In the current study, we examined whether lateral trunk flexion is associated with verticality misperception in patients with Parkinson's disease. We also identified the brain regions involved in lateral trunk flexion and altered verticality perception. In this cross-sectional study, we evaluated the verticality perception using the subjective visual vertical test in 81 patients with Parkinson's disease and 14 age-matched healthy controls. According to the 97.5th percentile upper reference limit of the body tilt angle in the healthy controls, patients with Parkinson's disease were grouped into 37 patients with lateral trunk flexion and 44 patients without lateral trunk flexion. The mean of absolute subjective visual vertical angles was compared between patients with Parkinson's disease with lateral trunk flexion, those without lateral trunk flexion, and the healthy controls, and the impact of verticality misperception on lateral trunk flexion was evaluated using multivariate logistic regression models. We further performed a voxel-wise comparison of regional cerebral blood flow using N-isopropyl-p-[¹²³I] iodoamphetamine single-photon emission computed tomography (height threshold of P < 0.001, uncorrected for multiple comparisons, extent threshold of 100 voxels) to identify the brain regions associated with lateral trunk flexion, and to investigate the relationship between verticality misperception and regional hypoperfusion. The mean of absolute subjective visual vertical angles was larger in patients with Parkinson's disease with and without lateral trunk flexion than in healthy controls (P < 0.001 and P < 0.001). Additionally, the subjective visual vertical angle was associated with the presence of lateral trunk flexion (odds ratio 2.25, 95% confidence interval 1.51-3.36, P < 0.001). The regional cerebral blood flow in patients with Parkinson's disease with lateral trunk flexion was decreased in the right inferior parietal lobule, right superior parietal lobule, right superior temporal gyrus, and right dorsal posterior cingulate cortex compared with those without lateral trunk flexion. The subjective visual vertical angle was inversely correlated with regional cerebral blood flow in these regions, except for the dorsal posterior cingulate cortex. Our study reveals that hypofunction in the right temporoparietal association cortices is involved in verticality misperception and the development of lateral trunk flexion in patients with Parkinson's disease. These results provide insights into potential therapeutic targets for addressing lateral trunk flexion.