Postural sway in patients with early Parkinson's disease performing cognitive tasks while standing

Objectives: We investigated postural sway in patients with early Parkinson's disease (PD) to test the hypothesis that the postural control system was affected already at an early stage of PD. Moreover, we identified cases of dysfunction of stereopsis in PD patients.

Methods: We examined 23 patients with early PD and 23 healthy, sex- and age-matched control subjects. Postural sway was measured with an accelerometer at the center of mass at the lower spine. Subjects were asked to stand quietly for 30 s under two usual conditions (eyes open and eyes closed) and two dual tasks conditions (eyes open with dual task, eyes closed with dual task). Stereopsis was assessed using the Titmus fly test.

Results: In the usual conditions, no differences were found between the control group and PD group. With increasing task difficulty, PD patients showed an increase of RMS values of sway acceleration, compared to control subjects. These differences reached significance during cognitive task performance. PD patients showed larger JERK values with increasing difficulty of the sway task which also reached significance during cognitive task performance. Relative to controls, PD patients showed decreased stereopsis function. But, there were no statistically significant correlations between log seconds of arc of the Titmus test and JERK, even during cognitive task performance.

Conclusion: Our results indicate that patients with early PD have subtle signs of postural instability when their attention is diverted or reduced. In addition, deficits of stereopsis may be common in early PD patients. St Abbreviations: ACC: Accelerometers; ANOVA: Analysis of variance; AP: Antero-posterior; COP: Center of pressure; EC: Eyes closed; ECDT: eyes closed with dual task; EO: Eyes open; EODT: Eyes open with dual task; GDS: Geriatric depression scale; JERK: Jerkiness of sway; ML: Medio-lateral; MMSE: Mini mental state examination; MoCA: Montreal cognitive assessment; PD: Parkinson's disease; PDAbS: PD Patients with abnormal stereopsis; PDNrS: PD Patients with normal stereopsis; PIGD: Postural instability and gait disorder; RMS: Root mean square; UPDRS: Unified Parkinson's disease rating scale.