Clinicians at UCSF validate nTMS for non-invasive preoperative language mapping

nTMS is "of immediate interest in the clinical management of subjects with eloquent brain tumors"

HELSINKI, Finland – May 21, 2013 -- A paperLanguage Mapping with Navigated Repetitive TMS: Proof of Technique and Validation published in the journal Neuroimage by Tarapore et al. at the University of California, San Francisco, USA compared non-invasive nrTMS (navigated repetitive TMS), magnetoencephalographic imaging and direct cortical stimulation (DCS) for language mapping in 12 adult patients with lesions around cortical language areas. The nTMS device used in the study was the Nexstim NBS System.

When compared with intraoperative DCS results, the sensitivity of nTMS was found to be 90%, specificity was 98%, the positive predictive value was 69% and the negative predictive value was 99%. The authors conclude that maps of language function generated with nTMS correlate well with those generated by DCS. Negative nTMS mapping also correlates with negative DCS mapping.

Language mapping using nTMS was found to be safe and well-tolerated. In this study, the clinicians adjusted stimulation intensity to a level each patient found tolerable. The investigators did not find any correlation between stimulator intensity and the number of language disturbance sites identified. Additionally, the investigators used the field navigation features of the NBS System to avoid stimulating cranial and facial nerves.

The authors discuss that, "the real contribution of nTMS is in the preoperative preparation that it allows. By mapping a subject before surgery, the surgeon can generate a precise map of potentially positive language sites, which then may be swiftly interrogated with DCS during surgery. Additionally, if the preoperative nTMS map shows clear speech arrest sites distant from the region of surgical exposure, the surgeon may have increased confidence in the reliability of a negative intraoperative DCS map". Additionally, the authors found that nTMS mapping can help with patient-surgeon discussions and help patients prepare for the experience of intraoperative speech arrest in a comfortable, low-stress environment.

In their conclusion, the authors find that, "nTMS may offer a lesion-based method for noninvasively interrogating language pathways and be valuable in managing patients with peri-eloquent lesions." They also conclude that, "nTMS is a useful modality for generating language maps non-invasively. It is thus of immediate interest in the clinical management of subjects with eloquent brain tumors; it also has wide-ranging implications in basic science and translational studies of cortical language representation and physiology."