Motor outcome after subcortical stroke: MEPs correlate with hand strength but not dexterity
Introduction
Previous studies employing transcranial magnetic stimulation (TMS) have shown that motor evoked potential (MEP) threshold and amplitude in the early stages after hemispheric stroke are predictors of motor recovery and functional outcome (Heald et al., 1993, Catano et al., 1995, Catano et al., 1996, Rapisarda et al., 1996, Escudero et al., 1998). Longitudinal studies have shown that recovery is associated with a reduction in MEP threshold and an increase in MEP amplitude and with improvement in MEP latency and central conduction time (Heald et al., 1993, Turton et al., 1996, Cicinelli et al., 1997, D'Olhaberriiague et al., 1997, Traversa et al., 2000, Byrnes et al., 1999, Byrnes et al., 2001, Boniface, 2001). Most of the previous follow-up studies have been carried out within the first few weeks or months after the stroke (Rapisarda et al., 1996, Turton et al., 1996, Cicinelli et al., 1997, Escudero et al., 1998, Traversa et al., 2000), or at 12 months (Heald et al., 1993, Turton et al., 1996), and there have been few longer-term TMS studies of motor recovery (Byrnes et al., 1999). In general, previous studies have relied upon Medical Research Council grading and functional scales to assess motor outcome and few studies have used quantitative measures of muscle strength and dexterity to assess the eventual degree of recovery (Turton et al., 1996).
In the present study we have investigated the relationship between MEP parameters and motor outcome in a group of patients with subcortical stroke who had experienced substantial clinical recovery of motor function. The aims of the study were to determine whether there is a correlation between MEP amplitude and threshold and motor performance, and whether MEP parameters after recovery correlate best with muscle strength or motor dexterity in the affected hand.
Section snippets
Subjects
Twenty-three patients (24–76 years of age, 6 female) who had suffered a single subcortical mono-hemispheric ischaemic stroke 1 month to 23 years previously (mean 6.3 years) were included in the study (Table 1). In all the responsible lesion was identified by computerized tomography or magnetic resonance imaging and was in the internal capsule in 15, striato-capsular in 3 and corona radiata or centrum semiovale in 5. Prior to entry into the study all subjects had a complete neurological
Results
The mean grip strength ratio (affected/unaffected hand) and McCarron ratio were both ∼0.9 (grip ratio mean 0.94, range 0.6–1.22; McCarron ratio mean 0.91, range 0.75–1.09), which were consistent with the significant degree of recovery in the strength and dexterity of the affected hand as shown by MRC grading and MAS scores. The McCarron and grip strength ratios were significantly correlated (r=0.38, P=0.036, Fig. 1A).
MEP threshold on the affected side was higher than on the unaffected side in 9
Discussion
The principal finding of the present study is that, in this group of substantially recovered subjects who had suffered a subcortical stroke, parameters of corticospinal excitability and conduction (viz. MEP threshold and amplitude) correlate well with hand strength but correlate poorly with measures of manual motor dexterity.
The importance of the corticospinal tract for the execution of voluntary movement and motor dexterity has been established on the basis of electrophysiological studies in
Acknowledgements
The authors are grateful to the neurologists who referred patients for the study, and to Dr S. Ghosh for helpful discussion. The study was supported by Project Grant 139048 from the National Health and Medical Research Council of Australia.
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