Abstract
Background.
After stroke, recovery of movement in proximal and distal upper
extremity (UE) muscles appears to follow different time courses,
suggesting differences in their neural substrates. Objective. We
sought to determine if presence or absence of motor evoked potentials
(MEPs) differentially influences recovery of volitional contraction and
strength in an arm muscle versus an intrinsic hand muscle. We also
related MEP status to recovery of proximal and distal interjoint
coordination and movement fractionation, as measured by the Fugl-Meyer
Assessment (FMA). Methods. In 45 subjects in the year following
ischemic stroke, we tracked the relationship between corticospinal tract
(CST) integrity and behavioral recovery in the biceps (BIC) and first
dorsal interosseous (FDI) muscle. We used transcranial magnetic
stimulation to probe CST integrity, indicated by MEPs, in BIC and FDI.
We used electromyography, dynamometry, and UE FMA subscores to assess
muscle-specific contraction, strength, and inter-joint coordination,
respectively. Results. Presence of MEPs resulted in higher
likelihood of muscle contraction, greater strength, and higher FMA
scores. Without MEPs, BICs could more often volitionally contract, were
less weak, and had steeper strength recovery curves than FDIs; in
contrast, FMA recovery curves plateaued below normal levels for both the
arm and hand.
Conclusions. There are shared and separate
substrates for paretic UE recovery. CST integrity is necessary for
interjoint coordination in both segments and for overall recovery. In
its absence, alternative pathways may assist recovery of volitional
contraction and strength, particularly in BIC. These findings suggest
that more targeted approaches might be needed to optimize UE recovery.
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