Evaluation of Changes in Preoperative Cortical Excitability by Navigated Transcranial Magnetic Stimulation in Patients With Brain Tumor

Abstract

<b>Background:</b> This prospective study aimed to evaluate the cortical excitability (CE) of patients with brain tumors surrounding or directly involving the <b>corticospinal tract</b> (CST) using navigated transcranial magnetic stimulation (nTMS). <b>Methods:</b> We recruited 40 patients with a single brain tumor surrounding or directly involving the CST as well as 82 age- and sex-matched healthy controls. The patients underwent standard nTMS and CE evaluations. Single and paired pulses were applied to the primary motor area (M1) of both affected and unaffected cerebral hemispheres 1 week before surgery. The CE parameters included resting motor threshold (RMT), motor evoked potential (MEP) ratio for 140 and 120% stimulus (MEP 140/120 ratio), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Motor outcome was evaluated on hospital discharge and on 30-day and 90-day postoperative follow-up. <b>Results:</b> In the affected hemispheres of patients, SICI and ICF were significantly higher than in the unaffected hemispheres (<i>p</i>=0.002 and <b><i>p</i></b> =0.009, respectively). The 140/120 MEP ratio of patients' unaffected hemispheres was lower than that in controls (<i>p</i>=0.001). Patients with glioblastomas (GBM) had a higher interhemispheric RMT ratio than patients with grade II and III gliomas ( <b><i>p</i></b> = 0.018). A weak correlation was observed among the RMT ratio and the preoperative motor score (<i>R</i> ² = 0.118, <i>p</i> = 0.017) and the 90-day follow-up ( <b><i>R</i></b> ^<b>2</b> = 0.227, <i>p</i> = 0.016). <b>Conclusion:</b> Using preoperative nTMS, we found that brain hemispheres affected by tumors had abnormal CE and that patients with GBM had a distinct pattern of CE. These findings suggest that tumor biological behavior might play a role in CE changes.