Correlation of impaired subjective visual vertical and postural instability in Parkinson's disease.

Perception of verticality is essential for postural control. On the other hand, postural instability is one of the cardinal features in Parkinson's disease (PD). Thus, the objective of this study was to evaluate the vertical perception using the subjective visual vertical test in PD patients with different degrees of postural instability and in different stages of disease. Forty five idiopathic PD patients were evaluated using the Unified Parkinson's Disease Rating Scale (UPDRS), the Hoehn and Yahr Scale, the clinical test for postural instability, and the subjective visual vertical test. Forty-five healthy individuals were evaluated in the control group. PD patients had a compromised perception of verticality and a disturbed processing of graviceptive pathways. Good correlation was also found between subjective visual vertical and postural instability. Patients with the worst postural instability had greater deviations of subjective visual vertical. There was also a positive correlation between subjective visual vertical and scores on the UPDRS and Hoehn and Yahr Scale, with good and reasonable degree of intensity, respectively. These findings suggest that the perception of verticality is affected in PD patients and this abnormal vertical perception and disturbed processing of graviceptive pathways are associated with postural instability and to a lesser degree with disease severity.