Axial perturbations evoke increased postural reflexes in Parkinson's disease with postural instability

To measure axially-evoked postural reflexes in 11 Parkinson's disease (PD) subjects, both stable and unstable, and to compare these with 13 age-matched controls.

We measured the short-latency electromyography (EMG) reflex effects of brief impulsive displacements applied to the upper sternum or C7 for tibialis anterior (TA) and soleus. Our subjects were studied standing normally and when leaning both forwards and backwards.

The initial mechanical effects of the stimuli were similar but the reflex responses for the unstable PD group were increased, even after allowing for the increased levels of tonic activation. For TA, unstable PD subjects had significantly larger responses than the stable PD group whose responses were in turn significantly larger than controls. For soleus, unstable PD subjects had significantly greater responses than controls.

These findings are consistent with previous evidence that exaggerated postural responses are characteristic of unstable PD subjects.

Increased postural reflexes are characteristic of unstable PD subjects and may contribute to the instability seen for these patients in response to larger perturbations.