Qualitative postural control differences in Idiopathic Parkinson’s Disease vs. Progressive Supranuclear Palsy with dynamic-on-static platform tilt

Objectives: We aimed to assess whether postural abnormalities in Progressive Supranuclear Palsy (PSP) and Idiopathic Parkinson’s Disease (IPD) are qualitatively different by analysing spontaneous and reactive postural control. Methods: We assessed postural control upon platform tilts in 17 PSP, 11 IPD patients and 18 healthy control subjects using a systems analysis approach. Results: Spontaneous sway abnormalities in PSP resembled those of IPD patients. Spontaneous sway was smaller, slower and contained lower frequencies in both PSP and IPD as compared to healthy subjects. The amount of angular body excursions as a function of platform angular excursions (GAIN) in PSP was qualitatively different from both IPD and healthy subjects (GAIN cut-off value: 2.9, sensitivity of 94%, specificity of 72%). This effect was pronounced at the upper body level and at low as well as high frequencies. In contrast, IPD patients’ stimulusrelated body excursions were smaller compared to healthy subjects. Using a systems analysis approach, we were able to allocate these different postural strategies to differences in the use of sensory information as well as to different error correction efforts. Conclusions: While both PSP and IPD patients show abnormal postural control, the underlying pathology seems to be different. Significance: The identification of disease-specific postural abnormalities shown here may be helpful for diagnostic as well as therapeutic discriminations of PSP vs. IPD.