Ankle proprioception and the relationship to rigidity in Parkinsons disease

IntroductionProprioceptive mechanoreceptor afferents form the basis for the perception of body position and muscle tone regulation. Parkinsons disease (PD) is associated with proprioceptive dysfunction. Proprioceptive dysfunction at the ankle impairs balance and gait. No comprehensive data exist characterizing the extent of ankle position sense dysfunction in PD and its relationship with abnormal muscle tone. Objectives(1) Quantify ankle position sense acuity in PD. (2) Determine the relationship between ankle position sense and muscle rigidity. MethodsSixteen people with mild to moderate PD and 16 age-matched controls participated. PD participants were OFF medication during testing. Using a 2-forced-choice psychophysical paradigm, a participants ankle was passively rotated to two distinct positions - a reference of 15{degrees} 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 (item 3.3). ResultsBoth median JND threshold (PD: 2.1{degrees}, controls: 1.5{degrees}) and UA (PD: 1.7{degrees}, controls: 1.1{degrees}) were significantly elevated in the PD group compared to controls (p < 0.05). Seven participants with PD (44%) had thresholds above the control group maximum. JND threshold correlated positively with lower extremity rigidity ({rho} = 0.50, p = 0.047). ConclusionPD 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.