gms | German Medical Science

Objective: Preoperative assessment of motor and language function using navigated transcranial magnetic stimulation (nTMS) is becoming increasingly popular in neurosurgical practice. The resting motor threshold (RMT) represents the cortical excitability and has been identified as predictor for the postoperative motor outcome. Thus, a reliable assessment of the RMT is crucial to integrate nTMS results into preoperative planning, but many neurosurgical patients take CNS-effective drugs that can potentially impact the accurate assessment of the RMT. The aim of the present study was to examine the effect of common drugs on the RMT in neurosurgical patients.

Methods: 648 patients (age: 53.1 ± 15.7, range 19-85 years; 296 females) were investigated preoperatively using nTMS due to brain tumors affecting the motor cortex and/or the corticospinal tract. Histologies included metastases (n = 167), gliomas (n = 373), meningiomas (n = 34), cavernomas (n = 19), AVMs (n = 17) and other (n = 38). The RMTs for both hands were recorded resulting in a sample size of 1298 observations. Linear mixed models were used to analyse the effect of drug intake on the RMT in a between-subjects design. Besides medication (antiepileptic drugs, benzodiazepines, corticoids or antidepressants), age, gender, hemisphere (tumor or healthy) and histology of the tumor were included in the analyses.

Results: There was considerable variation in the RMT across subjects (mean 35.7 ± 9.0, range 15-97%). There was no difference in RMTs between patients that took antiepileptic drugs compared to those that did not (p = 0.149), but RMTs increased when more than one antiepileptic drug was taken (p = 0.034). When looking at the specific drugs, only Carbamazepine led to a significant increase in the RMT (p < 0.001) and this effect was dependent on the dose (p = 0.027). Further, increased RMTs were observed under benzodiazepine intake (p < 0.001) and this effect did not vary between different benzodiazepines (p = 0.175). Corticoids (p = 0.245) or antidepressants (p = 0.235) did not influence the RMT. None of the previous effects was influenced by the histology.

Conclusion: Our results contrast with previous studies showing an effect of antiepileptic drugs on cortical excitability measured by the RMT. Only intake of Carbamazepine and benzodiazepines was associated with higher RMT values, while no other drug influenced the RMT. These results are strengthened by the large sample size of the present study.