Ankle proprioception and the relationship to rigidity in Parkinson's disease

Proprioceptive mechanoreceptor afferents form the basis for the perception of body position and muscle tone regulation. Parkinson's disease (PD) is associated with proprioceptive dysfunction. This study aimed to characterize the extent of ankle position sense dysfunction in PD and its relationship with abnormal muscle tone.

Sixteen people with PD and 16 controls participated. Using a 2-forced-choice psychophysical paradigm, a participant's ankle was passively rotated to two positions - a reference of 15° plantarflexion and a smaller amplitude comparison position. Subsequently, the user verbally indicated which position was perceived as more plantarflexed. From the stimulus-response data a just-noticeable-difference (JND) threshold and uncertainty area (UA) were derived as measures of ankle position sense acuity. Muscle rigidity was assessed using the MDS-UPDRS III scale.

Both median JND threshold and UA were significantly elevated in the group with PD compared to controls (p < 0.05). JND threshold correlated positively with lower extremity rigidity (p = 0.047).

PD can lead to reduced ankle position sense acuity. Lower proprioceptive acuity tended to be associated with higher rigidity, suggesting that PD broadly alters proprioceptive signal processing affecting both perception and regulation of muscle tone.

Impairments in proprioceptive processing contribute to both proprioceptive dysfunction and rigidity in PD.