Subjective postural vertical in Parkinson's disease with lateral trunk flexion

Patients with Parkinson's disease (PD) and associated lateral trunk flexion (LTF) cannot accurately perceive their own verticality.

We measured the subjective postural vertical in coronal plane (SPVc) angle on patients' ipsilateral and contralateral sides and combined to clarify the effects of SPVc on LTF. We also investigated effects of the SPVc angle on LTF severity.

Thirty-nine patients (aged 74.1 ± 7.6 years) were divided between those with mild LTF (LTF angle < 10°, n = 34) and those with moderate to severe LTF (LTF angle ≥ 10°, n = 5) for comparison of the LTF angle, SPVc angle on both sides, inter-measurement variation in the SPVc angle, and the LTF to SPVc angle ratio (SPVc ratio).

We found significant positive correlation between LTF and the SPVc angle on the combined (r = .54, P = .001), ipsilateral (r = .51, P = .002), and contralateral (r = .50, P = .002) sides. We found significant negative correlation between the LTF angle and the SPVc ratio on the combined SPVc (r = -.82, P = .001), ipsilateral (r = -.69, P = .001), and contralateral (r = -.75, P = .001) sides and between the LTF and ipsilateral side coefficient of variation (r = -.34, P = .038). SPVc angles on ipsilateral and contralateral sides were significantly greater in cases of moderate to severe LTF than in cases of mild LTF (P < .01).

Subjective postural vertical in coronal plane assessment may be useful for assessing patients with PD and associated LTF.