Quantifying motor symptoms in Parkinson's Disease: Limb tremor and postural sway interactions
ABSTRACT Background: Objectively quantifying the motor symptoms of Parkinson’s Disease (PD) is a prerequisite for determining disease progression and the effects of any treatment. Our research has combined clinical rating scales and movement recording technologies to develop reliable clinical and scientifically valid measures to quantify limb tremor and postural stability.
Method: The relation between resting tremor, postural tremor and postural sway was examined in 10 elderly and 8 PD subjects (on and off medication) who completed a unilateral and bilateral pointing task while standing on a force platform. Tremor was recorded from the hand and index finger segments of each arm using uniaxial accelerometers. All PD subjects were assessed using the UPDRS by direct examination and via video examination.
Results: Elderly subjects were able to dissociate the low frequency, high amplitude oscillations of whole body motion from tremor in the upper limb. Their frequency profile was characterized by a single peak between 0-1 Hz for postural sway and between 8-12 Hz for upper limb tremor. In contrast, upper limb tremor for PD subjects was between 5- 8 Hz and there was high coherence between upper limb tremor and postural sway which increased with tremor severity. PD subjects also exhibited increased coupling between the hand and finger of a single limb and between A/P and M/L sway. These measures are being correlated with standard UPDRS assessments of limb tremor and postural stability.
Conclusion: These objective measures in combination with video examination protocols will produce a systematic and objective instrument for research purposes.