Abstracts

Rationale: To discover a biomarker to predict seizure occurrence, intractable epilepsy and treatment response by using transcranial magnetic stimulation (TMS) in patients with brain tumour related epilepsy.Methods: Threshold tracking transcranial magnetic stimulation (TMS) was undertaken in 14 patients with primary brain tumours (PBT) following resection. The resting motor threshold (RMT), cortical silent period (CSP) and short interval intracortical inhibition (SICI) were measured in all patients. We stratified the data in four groups: focal hemisphere (tumour side) with epilepsy (Gr A), focal hemisphere without epilepsy (Gr B), non-focal hemisphere (normal side) with epilepsy (Gr C), non-focal hemisphere without epilepsy (Gr D). The results were compared between the groups and to 18 healthy controls.Results: The RMT was significantly reduced in Gr C (47.89± 2.01%, P<0.05) and Gr D (45.84 ±1.65%, P<0.01) when compared to healthy controls (55.74 ±1.83%). In addition, there was a significantly low averaged SICI, between interstimulus interval 1-7 ms, in Gr A (5.6 ± 3.83 %, P<0.05) and Gr C (10.1 ± 2.03%, P=0.085) when compared to healthy control (16.09± 2.05%). In contrast, there was no significant difference in the CSP duration between groups when compared to healthy controls.Conclusions: The findings in the present study reveal a significant reduction of inhibitory cortical functions in brain tumour patients with epilepsy; suggesting a dysfunction of GABAA mediated intracortical circuits. Importantly, these findings may be a predictor of intractable seizures in the “epileptic” group despite tumour resection. From a clinical perspective, the present study may be of therapeutic importance, providing guidance in the decision to continue antiepileptic medication despite resection of the tumour.