Postural control in Parkinson’s disease: subtype-specific effects of levodopa and the role of cognition and freezing of gait

Abstract

BACKGROUND:Levodopa effects on postural sway may vary between motor subtypes Parkinson’s disease (PD).

AIM:This study investigated the impact of Levodopa on postural sway and identified clinical predictors of postural sway in individuals with PD classified as either postural instability/gait difficulty (PIGD) or tremor dominant (TD).

METHODS:Thirty individuals with PD were classified as PIGD (n=12) or TD (n=18) subtypes. A subgroup of TD-participants without freezing of gait (FOG) was also analyzed (n=14) to control for FOG as a confounding factor. Participants stood as still as possible on a force plate for 30-seconds with closed-eyes both On- and Off-medication. Repeated-measures analyses of variance were used to compare groups and assess the effect of medication on postural sway. Backward regression analyses were conducted to identify the clinical predictors of postural sway in both medication states for each subtype.

RESULTS:Medication state significantly influenced postural sway in the PIGD group, with increased sway observed in the On-medication condition, while the sway in the TD group remained unchanged across medication states. In the TD group, postural sway under medication was predicted by disease duration and cognition performance. In the PIGD group, sway in the Off-medication state was predicted by motor severity and cognition performance. FOG was confirmed as a confounding factor in postural sway among TD participants.

INTERPRETATION:Levodopa affected postural balance only PIGD-subtype. Despite subtype differences in Levodopa effects, cognition emerged as a common predictor of postural sway between groups. Excluding participants with FOG strengthened the relationship between clinical characteristics and postural sway in the TD-subtype.