Dataset Information

Stroke subtype and motor impairment influence contralesional excitability.

ABSTRACT:

Objective

The nonlesioned motor cortex (M1NL) is thought to be hyperexcitable in patients with subacute or chronic stroke and offers a promising therapeutic target. However, whether M1NL excitability behaves the same for subcortical and cortical strokes is unknown. The aim of the present study was to determine whether cortical, or purely subcortical, strokes have a different effect on M1NL excitability.

Methods

We looked for correlations between the Fugl-Meyer (FM) score and M1NL resting motor threshold (RMTNL) in 34 stroke survivors classified according to lesion location (cortico-subcortical or purely subcortical). In addition to the FM, the Wolf Motor Score and motor power were measured.

Results

FM correlated with RMTNL for subcortical (r = 0.82; p = 0.001) but not for cortical strokes (r = 0.11; p = 0.62). Likewise, Wolf Motor Score (r = -0.62; p = 0.03) and motor power (r = 0.64; p = 0.023) were correlated with RMTNL for the subcortical group, but not for the cortical group.

Conclusion

We show that the impact on M1NL depends on lesion location and conclude that protocols aimed at reducing M1NL cortical excitability may be worth exploring for subcortical but not for cortical stroke.

SUBMITTER: Thickbroom GW

PROVIDER: S-EPMC4540249 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature

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Publications

Stroke subtype and motor impairment influence contralesional excitability.

Thickbroom Gary W GW Cortes Mar M Rykman Avrielle A Volpe Bruce T BT Fregni Felipe F Krebs H Igo HI Pascual-Leone Alvaro A Edwards Dylan J DJ

Neurology 20150717 6

<h4>Objective</h4>The nonlesioned motor cortex (M1NL) is thought to be hyperexcitable in patients with subacute or chronic stroke and offers a promising therapeutic target. However, whether M1NL excitability behaves the same for subcortical and cortical strokes is unknown. The aim of the present study was to determine whether cortical, or purely subcortical, strokes have a different effect on M1NL excitability.<h4>Methods</h4>We looked for correlations between the Fugl-Meyer (FM) score and M1NL ...[more]

PMID: 26187228

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Project description:The standard approach to brain stimulation in stroke is based on the premise that ipsilesional M1 (iM1) is important for motor function of the paretic upper limb, while contralesional cortices compete with iM1. Therefore, the approach typically advocates facilitating iM1 and/or inhibiting contralesional M1 (cM1). But, this approach fails to elicit much improvement in severely affected patients, who on account of extensive damage to ipsilesional pathways, cannot rely on iM1. These patients are believed to instead rely on the undamaged cortices, especially the contralesional dorsal premotor cortex (cPMd), for support of function of the paretic limb. Here, we tested for the first time whether facilitation of cPMd could improve paretic limb function in severely affected patients, and if a cut-off could be identified to separate responders to cPMd from responders to the standard approach to stimulation.In a randomized, sham-controlled crossover study, fifteen patients received the standard approach of stimulation involving inhibition of cM1 and a new approach involving facilitation of cPMd using repetitive transcranial magnetic stimulation (rTMS). Patients also received rTMS to control areas. At baseline, impairment [Upper Extremity Fugl-Meyer (UEFMPROXIMAL, max=36)] and damage to pathways [fractional anisotropy (FA)] was measured. We measured changes in time to perform proximal paretic limb reaching, and neurophysiology using TMS.Facilitation of cPMd generated more improvement in severely affected patients, who had experienced greater damage and impairment than a cut-off value of FA (0.5) and UEFMPROXIMAL (26-28). The standard approach instead generated more improvement in mildly affected patients. Responders to cPMd showed alleviation of interhemispheric competition imposed on iM1, while responders to the standard approach showed gains in ipsilesional excitability in association with improvement.A preliminary cut-off level of severity separated responders for standard approach vs. facilitation of cPMd.Cut-offs identified here could help select candidates for tailored stimulation in future studies so patients in all ranges of severity could potentially achieve maximum benefit in function of the paretic upper limb.

Project description:Background Spinal motoneurons may become hyperexcitable after a stroke. Knowledge about motoneuron hyperexcitability remains clinically important as it may contribute to a number of phenomena including spasticity, flexion synergies, and abnormal limb postures. Hyperexcitability seems to occur more often in muscles that flex the wrist and fingers (forearm flexors) compared to other upper limb muscles. The cause of hyperexcitability remains uncertain but may involve plastic changes in motoneurons and their axons. Aim To characterize intrinsic membrane properties of flexor carpi radialis (FCR) motor axons after stroke using nerve excitability testing. Methods Nerve excitability testing using threshold tracking techniques was applied to characterize FCR motor axon properties in persons who suffered a first-time unilateral cortical/subcortical stroke 23 to 308 days earlier. The median nerve was stimulated at the elbow bilaterally in 16 male stroke subjects (51.4 ± 2.9 y) with compound muscle action potentials recorded from the FCR. Nineteen age-matched males (52.7 ± 2.4 y) were also tested to serve as controls. Results Axon parameters after stroke were consistent with bilateral hyperpolarization of the resting potential. Nonparetic and paretic side axons were modeled by a 2.6-fold increase in pump currents (IPumpNI) together with an increase (38%–33%) in internodal leak conductance (GLkI) and a decrease (23%–29%) in internodal H conductance (Ih) relative to control axons. A decrease (14%) in Na+ channel inactivation rate (Aah) was also needed to fit the paretic axon recovery cycle. “Fanning out” of threshold electrotonus and the resting I/V slope (stroke limbs combined) correlated with blood potassium [K+] (R = −0.61 to 0.62, p< 0.01) and disability (R = −0.58 to 0.55, p < 0.05), but not with spasticity, grip strength, or maximal FCR activity. Conclusion In contrast to our expectations, FCR axons were not hyperexcitable after stroke. Rather, FCR axons were found to be hyperpolarized bilaterally post stroke, and this was associated with disability and [K+]. Reduced FCR axon excitability may represent a kind of bilateral trans-synaptic homeostatic mechanism that acts to minimize motoneuron hyperexcitability.

Dataset Information

Stroke subtype and motor impairment influence contralesional excitability.

Objective

Methods

Results

Conclusion

Publications

Stroke subtype and motor impairment influence contralesional excitability.

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