Objective: To determine how sensorimotor inhibition relates to objective measures of gait OFF and ON levodopa and how having Parkinson’s disease (PD) affects this relationship.

Background: Sensorimotor inhibition, as measured by short-latency afferent inhibition (SAI), is impaired in people with PD while ON levodopa. This interaction between levodopa and SAI remains poorly understood. For example, it is not known if giving levodopa to healthy controls also impairs SAI, nor if SAI relates to different gait characteristics in controls than PD. We hypothesize there is a drug-disease interaction that impairs sensorimotor inhibition, resulting in worsening of gait in PD while ON levodopa.

Method: 14 people with idiopathic PD and 15 healthy older adults had their sensorimotor inhibition assessed using the transcranial magnetic stimulation technique SAI. Six inertial sensors characterized gait during a two-minute walk. Participants were tested in both OFF and ON states. People with PD took their regular dose, controls took a single 25/100mg dose of carbidopa-levodopa. Independent and paired-samples t-tests compared between and within group differences for SAI. A repeated measures, general linear model compared gait characteristics between groups and conditions (OFF to ON). Spearman correlations assessed relationships between SAI and gait characteristics.

Results: The PD group had significantly worse SAI in their ON state (PD:83[21]; Control:64[16]; p=0.01) compared to controls. Neither group significantly changed SAI OFF to ON, though the change in states did have a moderate effect size for the PD group (OFF:74[26]; ON: 83[21]; Cohen’s d=0.50). Lateral trunk range of motion during walking was significantly smaller for PD than controls, both OFF (PD:6.2[2.0]; Control:7.9[1.9]; p=.03) and ON (PD:6.5[1.5]; Control:8.8[3.4]; p=.03). Levodopa did not change lateral trunk range in either group. SAI significantly related to lateral trunk range (ρ=-0.57; p=0.03) for the PD ON group.

Conclusion: Results showed that levodopa decreases sensorimotor inhibition in people with PD, but not control subjects and worse sensorimotor inhibition related to increased trunk rigidity, but only in people with PD. The interaction between SAI and dopaminergic pathways are altered in people with PD and this relationship may help explain fall risk while ON levodopa in people with PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/sensorimotor-inhibition-relates-to-gait-dysfunction-in-people-with-parkinsons-disease/