The
relationships between impairment, function, arm use and underlying
brain structure following stroke remain unclear. Although diffusion weighted imaging
is useful in broadly assessing white matter structure, it has limited
utility in identifying specific underlying neurobiological components,
such as myelin. The purpose of the present study was to explore relationships between myelination
and impairment, function and activity in individuals with chronic
stroke. Assessments of paretic upper-extremity impairment and function
were administered, and 72-hour accelerometer
based activity monitoring was conducted on 19 individuals with chronic
stroke. Participants completed a magnetic resonance imaging protocol
that included a high resolution T1 anatomical scan and a multi-component T2
relaxation imaging scan to quantify myelin water fraction (MWF). MWF
was automatically parcellated from pre- and post-central subcortical
regions of interest and quantified as an asymmetry ratio
(contralesional/ipsilesional). Cluster analysis was used to group more
and less impaired individuals based on Fugl-Meyer upper extremity
scores. A significantly higher precentral MWF asymmetry ratio was found
in the more impaired group compared to the less impaired group (p < 0.001). There were no relationships between MWF asymmetry ratio and upper-limb use. Stepwise multiple linear regression
identified precentral MWF asymmetry as the only variable to
significantly predict impairment and motor function in the upper
extremity (UE). These results suggest that asymmetric myelination in a
motor specific brain area is a significant predictor of upper-extremity
impairment and function in individuals with chronic stroke. As such,
myelination may be utilized as a more specific marker of the
neurobiological changes that predict long term impairment and recovery
from stroke.
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