Discordance between measured postural instability and absence of clinical symptoms in Parkinson's disease patients in the early stages of the disease

We compared postural performances in early stage Parkinson's disease (PD) patients and healthy subjects, and to determine if PD patients have infraclinical postural instability. Nine PD patients and 18 age- and sex-matched control subjects were recorded with open eyes (OE) and closed eyes (CE) using a force platform in static and dynamic conditions with a mobile platform allowing antero posterior and medio lateral oscillations. Oscillations of the mobile platform and balance strategy were quantified using both a force platform and the Vicon system. Under static conditions with both OE and CE, PD patients had a larger center foot pressure sway area than the control subjects (P = 0.007 and P = 0.04, respectively). Under dynamic conditions, the PD patients' sway area was greater than that of the control subjects in the CE antero posterior position (P = 0.04). Oscillations of the mobile platform were not different between the two groups. Lastly, all subjects used an ankle strategy, but PD patients had larger head oscillations than the control subjects. Early stage PD patients have an infraclinical postural instability which is compensated when it is more difficult to maintain good balance, suggesting that the neurological mechanisms of balance are partially still operating at this stage of the disease.