200 Section - Pupillary Responses to Transcranial Magnetic Stimulation can Persist Post Stroke and may be Sensitive to Spasticity Treatment with Botulinum Toxins

Botulinum neurotoxin (BoNT) injections for spasticity have been shown to affect cortical physiology by dampening the amplitude of transcranial magnetic stimulation (TMS) motor evoked potentials (MEP). However, when a stroke lesion interrupts the corticospinal tract, MEPs are not evocable (MEP-), presenting a challenge for studying cortical physiology. Previous work has demonstrated the nexus between pupil dilations after TMS and cortical excitability, though these pupillary responses to TMS have not been documented in patients with stroke. We aimed to assess if pupillary responses to TMS persist post stroke, even among MEP- patients, and to determine if this measure of cortical excitability is sensitive to spasticity treatment.


Design:

Participants with elbow and wrist spasticity treated with BoNT were recruited as part of a larger study. TMS was delivered over the ipsilesional hemisphere, at the first dorsal interossei (FDI) hotspot at 120% of their resting motor threshold. For MEP- participants, stimulation was delivered over the hand knob of the ipsilesional hemisphere at the maximal stimulator output. Pupil size was measured for 2-2.5 seconds before stimulation, and for 2 seconds following stimulation. Participants were assessed before, and six weeks after treatment.


Results:

Six participants completed assessments, four were MEP-. All demonstrated pupil dilation with TMS. Before treatment, participants had a mean maximal pupil dilation z-score of 4.12 (SD 1.09) with TMS. After six weeks, the mean maximal pupil dilation z-score reduced to 2.72 (SD 0.54). This reduction was significant and large (p=0.03, Cohen’s D=1.64).


Conclusion:

TMS induced pupil dilations occurred in every participant in the sample, including those without an evocable MEP. The large reduction in pupil dilation indicates that this measure of cortical excitability may be sensitive to spasticity treatments and may present a novel method for studying cortical physiology in patients with stroke affecting the corticospinal tract.