A novel TMS framework for assessing neurophysiological recovery at the subacute stage after stroke

Abstract

Objective

To use peri-threshold transcranial magnetic stimulation (TMS) intensities to elicit motor evoked potentials (MEPs) during the subacute stage after stroke and assess their association with upper limb motor recovery.

Methods

Twenty-five MEP+ patients participated in three sessions at 1, 3, and 6 months post-stroke. Single-pulse TMS across a range of stimulation intensities was used to elicit MEPs in four muscles of the paretic and non-paretic upper limb. At each timepoint, threshold matrices were constructed based on MEP amplitude and persistence. A matrix element was suprathreshold if five out of ten stimulations elicited MEPs ≥ 50 μV. A subthreshold element produced MEPs below this criterion. Dexterity was assessed using the nine hole peg test.

Results

There were fewer suprathreshold, and more subthreshold elements on the paretic compared to the non-paretic side. The number of suprathreshold elements on the paretic side increased between 1 and 6 months post-stroke. Neither sub- nor supra-threshold elements were associated with dexterity recovery.

Conclusion

The proportion of sub- and supra-threshold elements reflect neurophysiological recovery during the subacute stage after stroke. A threshold matrix framework can identify patients with stable versus dynamic neurophysiology post-stroke.

Significance

A compositional analysis framework can quantify neurophysiological recovery after stroke.