Repetitive transcranial magnetic stimulation (rTMS) may accelerate stroke recovery by modulating plasticity mechanisms. However, individual response variability currently limits its therapeutic potential. This study explored routine clinical neuroimaging to identify markers of response to rTMS early after stroke. Retrospective clinical imaging data were obtained within 3 days of stroke and analysed lesion characteristics from anatomical and diffusion weighted imaging. A form of rTMS, known as continuous theta-burst stimulation, was used as a plasticity probe to repeatedly activate synaptic connections in the ipsilesional motor cortex within weeks of stroke. The change in cortical excitability was quantified by measuring the amplitude of motor evoked potentials from the paretic hand. Clinical imaging data were evaluated in a regression model to identify significant predictors of change in cortical excitability following rTMS. Twenty-seven people with stroke (19 male) were evaluated. Apparent diffusion coefficient of the ipsilesional corticospinal tract was associated with the physiological response to rTMS. Covariates of baseline corticospinal excitability did not influence this association. Lower apparent diffusion coefficient of the ipsilesional corticospinal tract was associated with stronger suppression of corticospinal excitability. In contrast, higher values were associated with facilitation, potentially reflecting a metaplastic response. These findings suggest corticospinal tract integrity biases the direction and magnitude of the physiological response to rTMS. Neuroimaging may have value for explaining variability in rTMS response and should be considered in study design and interpretation.
Chau et al. (Wed,) studied this question.