Adaptations to Postural Perturbations in Patients With Freezing of Gait.

Kim Dockx,Surendar Devan,Sam Van Rossom,Elke Heremans,Esther M. J. Bekkers,Alice Nieuwboer,Sabine M. P. Verschueren

doi:10.3389/fneur.2018.00540

Abstract

Introduction: Freezing of gait (FOG) is a powerful determinant of falls in Parkinson's disease (PD). Automatic postural reactions serve as a protective strategy to prevent falling after perturbations. However, differences in automatic postural reactions between patients with and without FOG in response to perturbation are at present unclear. Therefore, the present study aimed to compare the response patterns and neuromuscular control between PD patients with and without FOG and healthy controls (HCs) after postural perturbations.Methods: 28 PD patients (15 FOG+, 13 FOG−) and 22 HCs were included. Participants stood on a moveable platform while random perturbations were imposed. The first anterior platform translation was retained for analysis. Center of pressure (CoP) and center of mass (CoM) trajectories and trunk, knee and ankle angles were compared between the three groups using the Statistical Parametric Mapping technique, allowing to capture changes in time. In addition, muscle activation of lower leg muscles was measured using EMG.Results: At baseline, FOG+ stood with more trunk flexion than HCs (p = 0.005), a result not found in FOG−. Following a perturbation, FOG+ reacted with increased trunk extension (p = 0.004) in comparison to HCs, a pattern not observed in FOG−. The CoM showed greater backward displacement in FOG− and FOG+ (p = 0.008, p = 0.027). Both FOG+ and FOG− showed increased co-activation of agonist and antagonist muscles compared to HCs (p = 0.010), with no differences between FOG+ and FOG−.Conclusions: Automatic postural reactions after a sudden perturbation are similar between PD subgroups with and without FOG but different from HCs. Reactive postural control, largely regulated by brain stem centers, seems to be modulated by different mechanisms than those governing freezing of gait. Greater differences in initial stance position, enhanced by joint stiffening, could however underlie maladaptive postural responses and increase susceptibility for balance loss in FOG+ compared to FOG−.

Highlights

Freezing of gait (FOG) is a powerful determinant of falls in Parkinson’s disease (PD)
PD patients were categorized as freezing of gait (FOG)+ (n = 16) if they scored 1 on item 1 of the new Freezing of Gait Questionnaire (NFOG−Q) or FOG− (n = 13) if they scored 0 on this item
Previous work using clinical balance assessments indicated that postural control is significantly worse in freezers and that this difference is most pronounced during reactive postural control in response to a leaning task [13]

Summary

Introduction

Freezing of gait (FOG) is a powerful determinant of falls in Parkinson’s disease (PD). When a stable posture is suddenly perturbed, the body must react and quickly adjust to recover balance These reactive postural adjustments are considered to be automatic responses, since the activation onset of muscle contraction is shorter than voluntary reaction times [1]. The release of automatic postural responses involves brainstem structures, including the mesencephalic locomotor region, as well as basal ganglia input, from the striatum [7,8,9]. These regions are known to be involved in freezing of gait (FOG) [10]. Larger impairments in reactive postural control may underlie the finding that when using clinical balance scales more severe balance deficiencies are apparent in FOG+ [12, 13]

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