The addition of the MEP amplitude of finger extension muscles to clinical predictors of hand function after stroke: A prospective cohort study.

BACKGROUND: Within the first 72 hours after stroke, active finger extension is a strong predictor of long-term dexterity. Transcranial magnetic stimulation may add prognostic value to clinical assessment, which is especially relevant for patients unable to follow instructions. OBJECTIVE: The current prospective cohort study aims at determining whether amplitude of motor evoked potentials of the extensor digitorum communis (EDC) can improve clinical prediction after stroke when added to clinical tests. METHODS: the amplitude of motor evoked potentials of the affected EDC muscle at rest was measured in 18 participants within 4 weeks after stroke, as were the ability to perform finger extension and the Fugl-Meyer Motor Assessment of the upper extremity (FMA_UE). These three determinants were related to the FMA_UE at 26 weeks after stroke (FMA_UE26), both directly, and via the proportional recovery prediction model. The relation between amplitude of the motor evoked potentials and FMA_UE26 was evaluated for EDC. For comparison, also the MEP amplitudes of biceps brachii and adductor digiti minimi muscles were recorded. RESULTS: Patients' ability to voluntarily extend the fingers was strongly related to FMA_UE26, in our cohort there were no false negative results for this predictor. Our data revealed that the relation between amplitude of motor evoked potential of EDC and FMA_UE26 was significant, but moderate (rs = 0.58) without added clinical value. The other tested muscles did not correlate significantly to FMA_UE26. CONCLUSIONS: Our study demonstrates no additional value of motor evoked potential amplitude of the affected EDC muscle to the clinical test of finger extension, the latter being more strongly related to FMA_UE26.

Can forearm muscle activity be selectively recorded using conventional surface EMG-electrodes in transcranial magnetic stimulation? A feasibility study.

OBJECTIVES: This feasibility study evaluates the effect of varying the position of conventional surface EMG-electrodes on the forearm when using Transcranial Magnetic Stimulation (TMS). The aim was to find optimal bipolar electrode positions for forearm extensor muscles, which would be clinically relevant to predict motor recovery after stroke. METHODS: In a healthy female subject, three rings of surface EMG-electrodes were placed around the dominant forearm, leading to 200 different electrode pairs. Both peripheral electrical stimulation and TMS were applied at suprathreshold intensities. RESULTS: With electrical stimulation of the median and radial nerve, similar waveform morphology was found for all electrode pairs, covering both flexors and extensors. Also with TMS, remarkable similarities between all electrode pairs were found, suggesting minimal selectivity. In both peripheral electrical stimulation and TMS, the curves became more irregular with decreasing inter-electrode distances. CONCLUSION: Neither with peripheral electrical stimulation nor with TMS it was possible to selectively record extensor or flexor forearm muscle activity using conventional surface EMG-electrodes. SIGNIFICANCE: Despite this negative result, the important role of the forearm extensor muscles in the prognosis of motor recovery after stroke warrants further research into novel methods for selectively recording muscle activity in TMS other than by conventional surface EMG.