Abstract
Mobility and balance impairments are a hallmark of multiple sclerosis (MS), affecting nearly half of patients at presentation and resulting in decreased activity and participation, falls, injuries, and reduced quality of life. A growing body of work suggests that balance impairments in people with mild MS are primarily the result of deficits in proprioception, the ability to determine body position in space in the absence of vision. A better understanding of the pathophysiology of balance disturbances in MS is needed to develop evidence-based rehabilitation approaches. The purpose of the current study was to (1) map the cortical proprioceptive pathway in vivo using diffusion-weighted imaging and (2) assess associations between proprioceptive pathway white matter microstructural integrity and performance on clinical and behavioral balance tasks. We hypothesized that people with MS (PwMS) would have reduced integrity of cerebral proprioceptive pathways, and that reduced white matter microstructure within these tracts would be strongly related to proprioceptive-based balance deficits. We found poorer balance control on proprioceptive-based tasks and reduced white matter microstructural integrity of the cortical proprioceptive tracts in PwMS compared with age-matched healthy controls (HC). Microstructural integrity of this pathway in the right hemisphere was also strongly associated with proprioceptive-based balance control in PwMS and controls. Conversely, while white matter integrity of the right hemisphere’s proprioceptive pathway was significantly correlated with overall balance performance in HC, there was no such relationship in PwMS. These results augment existing literature suggesting that balance control in PwMS may become more dependent upon (1) cerebellar-regulated proprioceptive control, (2) the vestibular system, and/or (3) the visual system.
Highlights
Multiple sclerosis (MS) is the most common chronic, nontraumatic neurological disorder of young adults, affecting approximately 400,000 people in the United States (Zwibel, 2009)
Participants were well matched for age and weekly physical activity; the people with MS (PwMS) group had significantly more females compared to the healthy controls (HC) group (χ2 = 4.5; P < 0.05)
Particular deficits in PwMS were observed within the anticipatory postural adjustment, sensory orientation, and dynamic gait domains, whereas reactive postural control performance was quite similar between groups
Summary
Multiple sclerosis (MS) is the most common chronic, nontraumatic neurological disorder of young adults, affecting approximately 400,000 people in the United States (Zwibel, 2009). Proprioceptive (somatosensory) feedback, principally supplied by primary muscle spindles (Ia), is critically important for balance control. Patients with peripheral neuropathy affecting 1a and 1b afferents show large body sway with eyes closed and delayed postural response latencies (Dickstein et al, 2001). Studies comparing balance control under different sensory feedback conditions (e.g., eyes closed, standing on a compliant surface, etc.) estimate that proprioception contributes 58–69% to body sway in standing (Lord et al, 1991). Ankle joint proprioception appears to be of particular importance, as it provides the most salient information regarding standing body sway (Fitzpatrick et al, 1994) and is a sensory feedback system significantly degraded in PwMS (Horak et al, 1990; Wylezinska et al, 2003; Cameron et al, 2008)
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