Rationale: Repetitive transcranial magnetic stimulation (rTMS) is used alone or in combination with physiotherapy for rehabilitation of stroke patients. TMS mapping can also quantify the excitability of the motor area in both the ipsilesional (IL) and contralateral (CL) hemisphere.
Objective: This study is the first to measure the dynamics of cortical excitability by TMS mapping before and after treatment with low-frequency (LF) rTMS in the contralesional hemisphere at three different timepoints. Furthermore, the patients were clinically evaluated during the same visit as the mapping to establish both short and long-term outcomes after rTMS treatment.
Methods and results: A total of 16 participants with acute ischemic stroke were assessed 10 days post-stroke by TMS mapping. The patients were randomized into two equal groups: a real rTMS group and a sham group. The rTMS group received LF-rTMS to the contralesional hemisphere for 10 days, starting on the first day after the first mapping. Each subject was also evaluated by mapping on days 45 and 90 after stroke onset. The primary clinical outcome measured was the Fugl-Meyer Assessment for Upper Extremity (FMA-UE) on days 10, 45 and 90 post-stroke. At 10 days after stroke onset, both groups presented low excitability in the lesion side and high excitability in the non-affected side. In the real rTMS group, at 45 days after stroke, a downward trend in the excitability of the contralesional hemisphere and an upward trend in the excitability of the lesioned side were observed. At 90 days after stroke, a tendency toward balanced excitability between both hemispheres was observed. In the sham group, at both 45 and 90 days, we observed increased excitability in the non-affected side compared to the side with the lesioned motor area. At 45 days, the real rTMS group demonstrated a better recovery of the upper limb motor function than the sham group, but at 90 days, there was no significant difference between the two groups.
Discussion: These results demonstrated that LF-rTMS treatment enhances rebalance of the excitability patterns in both hemispheres and led us to question the "one size fits all" approach widely used in rTMS interventions.
Abbreviations: Amax = maximum amplitude, Amean = AM = averaged amplitude, APB = abductor pollicis brevis, CL = contralesional, DTI = diffusion tensor imaging, EEG = electroencephalography, EMG = electromyography, FMA-UE = Fugl-Meyer Assessment for Upper Extremity, HS = hot spot, IHC = interhemispheric functional connectivity, IL = ipsilesional, LF-rTMS = low-frequency repetitive transcranial magnetic stimulation, MCA = middle cerebral artery, MEP(s) = motor evoked potential(s), NIBS = non-invasive brain stimulation, rMT = resting motor threshold, RP = responsive points, rTMS = repetitive transcranial magnetic stimulation, TMS = transcranial magnetic stimulation.
Keywords: cortical excitability; low-frequency rTMS; subacute ischemic stroke.