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| Navigated Transcranial Magnetic Stimulation | |
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| Description: |
Navigated transcranial magnetic stimulation (nTMS) is a noninvasive method of mapping functional cortical areas before neurosurgery. The Nexstim navigated brain stimulation system integrates transcranial magnetic stimulation with magnetic resonance imaging (MRI)-based neuronavigation to localize motor or language-related cortical sites. Mapping data may be exported for surgical planning, neuronavigation, and diffusion tensor imaging tractography. In individuals with brain tumors involving or near eloquent cortex, the clinical purpose is to improve preoperative risk assessment, guide the surgical approach, and support maximal safe resection while reducing permanent neurologic deficits.
Background
Maximal safe resection is a central goal in brain tumor surgery. Greater extent of resection may improve tumor control and survival in selected gliomas and metastases, but neurologic injury can reduce quality of life, delay adjuvant therapy, and worsen outcomes. Lesions involving motor or language areas require individualized planning to balance resection goals against the risk of permanent deficit, which depends on accurate preoperative identification of functional cortex to guide the surgical approach, tailor craniotomy size, and counsel the patient. Mapping of brain function may be used to help determine the surgical approach, estimate the risk of resection, guide the size and location of the craniotomy, and counsel patients about potential postoperative deficits. Intraoperative direct cortical stimulation or direct electrical stimulation is generally considered the reference standard for identifying eloquent cortex, but it is performed during surgery. Preoperative mapping techniques may provide information before surgery, but intraoperative stimulation is still commonly used to confirm functional boundaries when clinically indicated.
Functional magnetic resonance imaging is commonly used for noninvasive localization of brain function. Functional magnetic resonance imaging identifies areas of altered blood oxygenation during performance of a task, such as movement or language testing. These signals indicate cortical regions involved in the task, but they do not necessarily establish that a region is essential for that function. Results may also be affected by patient cooperation, paresis, tumor-related vascular changes, edema, and task performance. Magnetoencephalography is another noninvasive mapping technique which records magnetic fields generated by neuronal activity and may be used to localize functional regions, including sensory or motor areas. Diffusion tensor imaging tractography may be used to estimate the course of white matter pathways, such as the corticospinal tract or language-related tracts. Tractography is an anatomic imaging technique and does not itself determine whether a cortical or subcortical site is functionally essential.
Navigated transcranial magnetic stimulation is an adjunctive noninvasive technique that combines transcranial magnetic stimulation with magnetic resonance imaging-based neuronavigation as a complement to intraoperative direct cortical or direct electrical stimulation. A magnetic coil delivers stimulation to targeted cortical regions while a navigation system estimates the location, direction, and strength of the electric field relative to the patient’s brain imaging. For motor mapping, single-pulse navigated transcranial magnetic stimulation is applied to cortical regions while motor evoked potentials are recorded from target muscles using electromyography. Sites where stimulation produces a reproducible motor response are considered motor-positive and may be exported to neuronavigation systems for surgical planning or used as seed regions for corticospinal tract tractography. For language mapping, repetitive navigated transcranial magnetic stimulation is delivered during a language task, commonly object naming. Stimulation-associated naming or speech errors are classified to identify cortical regions where stimulation disrupts language-task performance. Language-mapping protocols vary across studies, including stimulation frequency, number of pulses, intensity, picture-to-trigger interval, language task, and error-threshold rules.
Regulatory Status
Devices for nTMS have been cleared for marketing by the U.S. Food and Drug Administration (FDA) for diagnostic preprocedural mapping uses under the evoked response electrical stimulator classification. In December 2009, the Nexstim eXimia Navigated Brain Stimulation System received 510(k) clearance (K091457) for noninvasive mapping of the primary motor cortex of the brain to its cortical gyrus. The device provides information that may be used in the assessment of the primary motor cortex for preprocedural planning and is not intended for use during a surgical procedure.
In May 2012, the Nexstim Navigated Brain Stimulation System 4 and Nexstim NBS System 4 with NEXSPEECH received 510(k) clearance (K112881). The NBS System 4 was cleared for noninvasive mapping of the primary motor cortex for preprocedural planning. NEXSPEECH, when used with the NBS System 4, was cleared for noninvasive localization of cortical areas that do not contain essential speech function and provides information that may be used in presurgical planning for patients undergoing brain surgery. The FDA summary states that intraoperatively, localization information provided by NEXSPEECH is intended to be verified by direct cortical stimulation and that the device is not intended for use during a surgical procedure. Although Nexstim currently markets the NBS 6 System for diagnostic presurgical mapping, no additional FDA 510(k) clearances for NBS 6 diagnostic brain-mapping indications were identified beyond the predicate clearances.
Coding
There is not a specific CPT code for this procedure. It may be billed with CPT code 64999
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Policy/ Coverage: |
Effective April 22, 2026
Does Not Meet Primary Coverage Criteria Or Is Not Covered For Contracts Without Primary Coverage Criteria
Navigated transcranial magnetic stimulation for all purposes, including but not limited to the preoperative evaluation of individuals being considered for brain surgery when localization of eloquent areas of the brain (e.g., controlling verbal or motor function) is an important consideration in surgical planning, does not meet member benefit certificate Primary Coverage Criteria that there be scientific evidence of effectiveness in improving health outcomes and is not covered.
For members with contracts without Primary Coverage Criteria, navigated transcranial magnetic stimulation is considered Not Medically Necessary or is investigational and is not covered for all purposes, including but not limited to the preoperative evaluation of individuals being considered for brain surgery when localization of eloquent areas of the brain (e.g., controlling verbal or motor function) is an important consideration in surgical planning. Not Medically Necessary or Investigational services are specific contract exclusions in most member benefit certificates of coverage
Click the following link to view the InterQual® criteria:
Effective December 2013 - April 21, 2026
Does Not Meet Primary Coverage Criteria Or Is Investigational For Contracts Without Primary Coverage Criteria
Navigated transcranial magnetic stimulation for all purposes, including but not limited to the preoperative evaluation of patients being considered for brain surgery, when localization of eloquent areas of the brain (e.g., controlling verbal or motor function) is an important consideration in surgical planning does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
For members with contracts without primary coverage criteria, navigated transcranial magnetic stimulation is considered investigational for all purposes, including but not limited to the preoperative evaluation of patients being considered for brain surgery, when localization of eloquent areas of the brain (e.g., controlling verbal or motor function) is an important consideration in surgical planning. Investigational services are specific contract exclusions in most member benefit certificates of coverage.
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| Rationale: |
Test-retest reliability in healthy volunteers
In some studies, navigated transcranial magnetic stimulation (nTMS) has been repeated in subjects over a relatively short interval in time to evaluate whether the test is reliable; that is, produces a similar result. In these studies, it is assumed that nothing in the subject has changed, and any difference in result is due to variations in the testing procedure and any natural variability in the subject.
In a study by Forster et al., 12 healthy participants underwent nTMS in 2 different sessions, separated in time an average of 10 days (Forster, 2013). Five muscle groups in the upper and lower extremity in each subject were stimulated, and the hotspots (points of optimal stimulation) and center of gravity (amplitude-weighted center of area sensitive to stimulation) for each subject were identified. The mean distance between these points between sessions for each muscle were calculated. The intraclass coefficient in the x-axis (mediolateral) and the y-axis (anteroposterior) for each muscle was calculated. Overall, across all muscles, the mean difference in hotspot location between sessions was 0.79 +- 0.47 cm. The mean difference in center of gravity location was 0.57+-0.32 cm. The intraclass coefficients in the antero-posterior axis ranged from 0.54 to 0.89, consistent with moderate to excellent reliability. In the mediolateral axis, intraclass coefficients ranged from 0.11 to 0.89, with several of the coefficients less than 0.49, which is generally regarded as poor reliability.
A study by Weiss et al. also evaluated the reliability of nTMS and functional MRI in 10 healthy subjects (Weiss, 2013). Muscles in the hand, foot and face were evaluated. nTMS was not feasible in a high proportion of subjects for evaluating the face and tongue due to technical constraints and other artifacts. Functional magnetic resonance imaging (fMRI) on the other hand, produced interpretable findings for all muscle groups in all sessions. The mean difference in hotspot location, as identified by nTMS between sessions was 10.8 +- 1.9 mm. The mean difference in maximum activation, as identified by fMRI between sessions was 6.2+-1 mm, thus showing that fMRI was more reliable than nTMS in locating a specific point associated with a particular muscle. In another type of analysis in which the spatial extent of a particular muscle activity was mapped by either nTMS or fMRI, neither technique yielded reliable results. The extent of spatial overlap between sessions was very low for either technique (less than 32% for both) and the intraclass correlation coefficients were also both less than 50%, indicating poor reliability.
Studies of nTMS in brain tumor patients
Most studies of nTMS are small case series of brain tumor patients, which are not ideal studies to ascertain diagnostic characteristics. Due to the use of nTMS and/or other methods to identify the motor or language centers in the cortex and determine the surgical approach, the reference standard of direct cortical stimulation (DCS) may be biased. The DCS procedure may be limited or altered because of the tumor resection or other surgical factors. It is not possible to verify all the nTMS sites identified, because the surgical field is limited. Because of this necessarily limited verification, it is difficult to ascertain diagnostic characteristics of nTMS.
Comparisons to Direct Cortical Stimulation
Picht et al. evaluated 17 patients with brain tumors with both nTMS and DCS. Both techniques were used to elicit “hotspots,” the point at which either nTMS or DCS produced the largest electromyographic response in the target muscles (Picht, 2011). Target muscles were selected based on the needs of each particular patient in regard to tumor location and clinical findings. The intraoperative DCS locations were chosen independently of nTMS, and the surgeon was not aware of the nTMS hotspots. There were 37 muscles in the 17 patients for which both nTMS and DCS data were available. The mean (+- SEM) distance between the nTMS and DCS hotspots was 7.83 +- 1.18 mm for the abductor pollicis brevis muscle and 7.07 +- 0.88 mm for the tibialis anterior muscle. The 95% confidence interval (CI) for the mean distance was 5.31 to 10.36 mm. When DCS was performed during surgery, there was large variation in the number of stimulation points, and the distance between nTMS and DCS was much less when a larger number of points were stimulated.
Forster et al. performed a similar study in 11 patients (Forster, 2011). fMRI was also performed in these patients. The distance between corresponding nTMS and DCS hotspots was 10.49 +- 5.67 mm. The distance between the centroid of fMRI activation and DCS hotspots was 15.03+- 7.59 mm. However, it is not clear whether there were hotspots with either device that cannot be elicited with the other. There were at least 2 excluded patients in whom nTMS hotspots could not be elicited in which DCS elicited a response.
Another study by Tarapore et al. evaluated distance between nTMS and DCS hotspots (Tarapore, 2012). Among 24 patients who underwent nTMS,18 of whom underwent DCS, 8 motor sites in 5 patients were corresponding. The median distance between nTMS and DCS hotspots was 2.13+- 0.29 mm. In the craniotomy field in which DCS mapping was performed, DCS did not find any new motor sites that TMS failed to identify. The study also evaluated magnetoencephalography (MEG); the median distance between MEG motor sites and DCS was 12.1 ± 8.2 mm.
Mangravati et al. also evaluated the distance between nTMS and DCS hotspots in 7 patients (Mangraviti, 2012). It cannot be determined from the study report how many hotspots are compared and how many potential comparisons are not available due to failure of either device to find a particular hotspot. It appears that the mean distance between hotspots is based on the locations of hotspots for 3 different muscles. The overall mean difference between nTMS and DCS was 8.47 mm. This was smaller than the mean difference between the centroid of fMRI activation and DCS hotspots of 12.9 ± 5.7 mm.
Krieg et al. also evaluated nTMS in comparison to DCS in a study of 14 patients (Krieg, 2012). However, the navigation device employed appears to be different than the FDA-approved device. In addition, the comparison of nTMS to DCS uses a different methodology. Both nTMS and DCS were used to map out the whole volume of the motor cortex, and a mean difference between the borders of the edge of the mapped motor cortex was calculated. The mean distance between the two methods was 4.4 ± 3.4 mm. These studies assessing the distance between nTMS and DCS hotspots appear to show that stimulation sites in which responses can be elicited from both techniques tend to be mapped within 1 cm of each other. This distance tends to be less than the distance between fMRI centers of activation and DCS hotspots. It is difficult to assess the clinical significance of these data, in terms of the utility of the information, on presurgical planning.
Language mapping compared to Direct Cortical Stimulation
A study by Picht et al. attempted to evaluate the accuracy of nTMS for identifying language areas (Picht, 2013). Twenty patients underwent evaluation of language areas over the whole left hemisphere, which was divided into 37 regions. DCS was necessarily performed only in areas accessible in the craniotomy site. In a total of 160 regions in the 20 patients, data for both methods were available. Using DCS as the reference standard, there were 46 true positives, 83 false positives, 26 true negatives, and 5 false negatives. Considering the analysis as 160 independent data points for each brain region, nTMS had a sensitivity of 90.2%, specificity of 23.8%, positive predictive value of 35.6% and negative predictive value of 83.9%. An analysis of regions considered to be in the classic Broca’s area showed a sensitivity of 100%, specificity 13.0%, positive predictive value of 56.5%, and negative predictive value of 100%. Another study by Tarapore et al. of 12 subjects also evaluated nTMS for identifying language areas (Tarapore, 2013). In addition to nTMS, MEG was also evaluated. A total of 183 regions were evaluated with both nTMS and DCS. In these 183 regions, using DCS as the reference standard, there were 9 true positives, 4 false positives, 169 true negatives and 1 false negative. This translates to a sensitivity of 90%, specificity of 98%, a positive predictive value of 69% and a negative predictive value of 99%.
The study by by Picht et al. showing the very high number of false positives raises concerns about the utility of nTMS for identifying language areas. Even if nTMS is used to rule out areas in which language areas are unlikely, the sensitivity of 90.2% may result in some language areas not appropriately identified.
Studies of clinical utility
There are no formal comparison studies evaluating nTMS versus other strategies without nTMS in affecting health outcomes in patients being considered for surgical resection of brain tumors. Such studies would be difficult to design and may not be practical or ethical to carry out. Given that results of diagnostic workups of brain tumor patients may result in differences in which patients are operated on, the counseling given to patients, and the type of surgery performed, it would be difficult to compare outcomes of groups of patients with very qualitatively different outcomes. For example, it is difficult to compare the health outcome of a patient who ends up not being operated on, who conceivably has a shorter overall lifespan but a short period of very high quality of life, to a patient who undergoes operation but has some moderate disability afterward, but a much longer overall lifespan.
A study by Picht et al. attempts to determine the clinical utility of nTMS by assessing whether a change in management occurred as a result of knowledge of nTMS findings (Picht, 2012). In this study, surgeons first made a surgical plan based on all known information without nTMS findings. After being made aware of nTMS findings, the surgical plan was reformulated if necessary. According to this protocol, in 73 patients with brain tumors in or near the motor cortex, nTMS was judged to have changed the surgical indication in 2.7%, changed the planned extent of resection in 8.2%, modified the approach in 16.4%, added awareness of high-risk areas in 27.4%, added knowledge that was not used in 23.3%, and only confirmed the expected anatomy in 21.9%. The first 3 categories in which it was judged that the surgery was altered because of nTMS findings were summed up to determine “objective benefit,” which was 27.4%.
Summary
Overall, the literature on navigated transcranial magnetic stimulation (nTMS) is at a very preliminary stage of demonstrating effectiveness. Relatively small studies have demonstrated the distance between nTMS hotspots and direct cortical stimulation (DCS) hotspots for the same muscle. Although the average distance in most studies is 1 cm or less, this does not take into account the degree of error in this average distance, or whether there are missed hotspots. It is difficult to fully verify nTMS hotspots because only exposed cortical areas can be verified with DCS. Limited studies of nTMS to evaluate language areas show a very high rate of false positives, at least in one study. One study has attempted to demonstrate how clinical decision making has been changed as a result of nTMS results. This type of study does not provide strong evidence of the efficacy of nTMS.
2014 Update
A literature search conducted through November 2014 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
Schmidt et al (2014) in Germany designed a study to examine confounding factors that affect Ntms performance (Schmidt, 2014).
In a 3-part design, investigators differentiated variance due to physiological factors (eg, tissue conductivity, brain rhythms, cognitive state, peripheral sensory input, preinnervation, brain dysfunction) from physical variation of the nTMS device (ie, coil location, orientation, and tilt, stimulation strength). Twenty healthy volunteers participated in 2 experiments to compare targeted stimulation (optimal stimulus location, orientation, and tilt parameters) with nontarget-controlled stimulation. Four healthy volunteers participated in a third experiment of maximal physiological confounding variance (eg, patients were instructed to maximally contract the target muscle). Spatial resolution of nTMS (defined as variation in the area of cortical stimulation that leads to maximum muscle contraction) was found to be approximately 5 mm so that “even small physical fluctuations can confound the statistical comparison of corticospinal excitability measurements” (Schmidt, 2014).
The authors recommended step-wise regression to partition physical from physiological variance in nTMS results and to produce more interpretable data.
Studies in Patients with Brain Lesions
Most studies of nTMS are small case series of patients with brain tumors (Mangarviti, 2013; Opitz, 2014; Rizzo, 2014),
cavernous angiomas (Paiva, 2013), arteriovenous malformations (Kato, 2014)
or other brain lesions; these are not ideal studies to ascertain diagnostic
characteristics. Because of the use of nTMS and/or other methods to identify motor or language centers
in the cortex to determine surgical approach, the reference standard of direct cortical stimulation (DCS)
may be biased; that is, the DCS procedure may be limited or altered because of the tumor resection or
other surgical factors. It is not possible to verify all nTMS sites identified, because the surgical field is
limited. Because of this necessarily limited verification, it is difficult to ascertain diagnostic characteristics
of nTMS. nTMS is being studied as a technique to augment preoperative detection of motor corticospinal tracts (CSTs), which are currently identified using diffusion tensor imaging (DTI), an MRI technique (Conyi, 2014; Frey, 2014).
Conti et al (2014) compared the size and location of (cortical) motor maps determined by the cortical end of CSTs, identified using DTI only and nTMS-DTI, to nTMS maps (Conti, 2014).
Twenty patients who underwent brain surgery at a single center in Italy were prospectively enrolled. All brain lesions (70% brain tumors [glioma, astrocytoma, glioblastoma multiforme], 20% cavernous angioma, 10% metastasis) were located within 10 mm of the motor cortex. nTMS-DTI was performed the day before surgery, and standard DTI was obtained after surgery using preoperative imaging data. Direct subcortical stimulation (functional tractography) was applied to confirm tract location. Overlap between nTMS cortical maps and cortical end-regions of CSTs was greater with nTMS-DTI compared with standard DTI (90% vs 58%). Direct subcortical stimulation confirmed CST location in all patients. A potential limitation of the study is lack of DCS to confirm nTMS-determined motor maps. Larger comparative studies with clinical outcomes are needed to assess the clinical relevance of these results.
nTMS for Language Mapping
A research group in Germany published 2 studies of nTMS for mapping cortical language sites, one in healthy volunteers
and one in patients with brain tumors (Krieg, 2014).
In a case series of 10 healthy volunteers, nTMS test-retest reliability varied across error type (eg, neologism, semantic error) and cortical region (ie, anterior or posterior), but overall, both intra- and interobserver reliability were low (range of concordance correlation coefficients: intraobserver, –0.222-0.505; interobserver, –0.135-0.588) (Sollmann, 2013).
In a case report of 3 patients with language-eloquent brain tumors who underwent nTMS and DCS for both initial surgery and repeat surgery for recurrence, nTMS performance characteristics varied by definition of a positive nTMS finding (ie, a language error made in response to stimulation) (Krieg, 2014). For positivity defined by error rates (percentage of stimulations that produced errors) ranging from 5% to 25%, sensitivity was 90% to 10%, specificity was 28% to 89%, PPV was 21% to 17%, and NPV was 93% to 82%. Plasticity of language areas in both healthy volunteers and in patients with brain lesions was identified as a source of variation in nTMS studies across time. As noted in one review, the language network appears to spread over both hemispheres, increasing the complexity of presurgical language mapping (Picht, 2014).
The Nexstim website21 lists 2 single-center studies from Germany that compared clinical outcomes in patients with motor-eloquent brain tumors who underwent surgical resection with or without preoperative nTMS (Frey, 2014; Kreig, 2014). Both studies used historical controls. Frey et al (2014) enrolled 250 consecutive patients who underwent nTMS preoperative mapping and identified 115 similar historical controls (Frey, 2014).
Fifty-one percent of the nTMS group and 48% of controls had WHO grade II to IV gliomas; remaining patients had brain metastases from other primary cancers or other lesions. Intraoperative motor cortical stimulation to confirm nTMS findings was performed in 66% of the nTMS group. British Medical Research Council and Karnofsky scales were used to assess muscle strength and performance status, respectively. Outcomes were assessed at postoperative day 7 and then at 3-month intervals. At 3 months follow-up, 6.1% of the nTMS group and 8.5% of controls had new postoperative motor deficits (chi-square test, p=NS); changes in performance status postoperatively also were similar between groups. Other outcomes were reported for patients with glioma only (n=128 nTMS patients, n=55 controls). Based on postoperative MRI, gross total resection was achieved in 59% of nTMS patients and in 42% of controls (chi-square test, p<0.05). At mean follow-up of 22 months (range, 6-62) in the nTMS group and 25 months (range, 9-57) in controls, mean PFS was similar between groups (mean PFS, 15.5 months [range, 3-51] nTMS vs 12.4 months [range, 3-38] controls; statistical test for survival outcomes not specified, p=NS). In the subgroup of patients with low-grade (grade II) glioma (n=38 nTMS patients, n=18 controls), mean PFS was longer in the nTMS group (mean PFS, 22.4 months [range, 11-50] nTMS vs 15.4 months [range, 6-42] controls; p<0.05), and new postoperative motor deficits were similar (7.5% vs 9.5%, respectively; chi-square test, p=NS). Overall survival did not differ statistically between treatment groups. Interpretation of these findings is limited by: the single-center setting (because nTMS is an operator-dependent technology, applicability may be limited), use of historical controls (surgeon technique and practice likely improved over time), selective outcome reporting (survival outcomes in glioma patients only), and uncertain validity of statistical analyses (primary outcome not identified, no correction for multiple testing, statistical tests not identified). In an accompanying editorial, Jensen outlined the following additional issues complicating interpretation of the study results (Jensen, 2014):
Although groups were similar in adjuvant chemotherapy and radiation treatments received, molecular tumor profiles that could impact survival outcomes were not reported.
In the second study from Germany, Krieg et al (2014) enrolled 100 consecutive patients who underwent nTMS preoperative mapping and identified 100 historical controls who were matched for tumor location, preoperative paresis, and histology (Krieg, 2014). Most patients had glioblastoma (37%), brain metastasis (24%), or astrocytoma (29%). Data analysis was performed blinded to group assignment. The primary efficacy outcome was not specified. Median follow-up was 7.1 months (range, 0.2–27.2) in the nTMS group and 6.2 months (range, 0.1–79.4) in controls. Incidence of residual tumor by postoperative MRI was less in the nTMS group compared with controls (22% vs 42%; odds ratio [OR]=0.38 [95% CI, 0.21 to 0.71]). Incidence of new surgery-related transient or permanent paresis did not differ between groups. However, “when also including neurological improvement [undefined] in the analysis,” more patients in the nTMS group improved (12% nTMS vs 1% controls), and similar proportions of patients worsened (13% nTMS vs 18% controls) or remained unchanged (75% nTMS vs 81% controls; Mann-Whitney-Wilcoxon test, p=0.006). Limitations of this study include the single-center setting, use of historical control, uncertain outcome assessments (“neurological improvement” not defined), and uncertain validity of statistical analyses (primary outcome not identified, no correction for multiple testing).
In his editorial, Jensen challenged the assertion that randomized trials of nTMS would be unethical, suggesting instead that equipoise exists about the best among several noninvasive mapping techniques (fMRI, magnetoencephalography, nTMS) (Jensen, 2014). Krieg et al concurred, stating that “a randomized trial on the comparison with the gold standard of intraoperative mapping seems mandatory to gain level I evidence for this modality” (Krieg, 2014).
Ongoing and Unpublished Clinical Trials
A search of online site ClinicalTrials.gov, found 1 ongoing RCT of nTMS, the NICHE trial (NCT02089464), sponsored by Nexstim (Helsinki, Finland). NICHE compares active with sham nTMS for the treatment of post-stroke motor impairment. Expected enrollment is 200 patients, and estimated completion date is July 2016.
2016 Update
A literature search conducted through October 2016 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
Safety of nTMS
Tarapore and colleagues evaluated the safety of nTMS in a large multicenter series of 733 patients (Tarapore, 2016).
Patients had tumors in eloquent or perieloquent regions of the brain and underwent nTMS as part of presurgical planning. nTMS frequencies of 5, 7 and/or 10 Hz were used. A total of 537 patients underwent single pulse motor mapping, 38 had repetitive-pulse language mapping, and 158 had both of these. nTMS was successfully completed in all patients. No seizures (focal, complex or generalized) were reported and no patients reported hearing changes, cognitive or neuropsychological changes, or other transient adverse effects. Headache, reported by 28 patients (6%). was the most commonly reported adverse effect. A total of 141 of 196 patients (72%) completed questionnaires after the procedure and 131 of these (93%) reported discomfort during the procedure. Using a visual analogue scale (VAS) of 1 to 10, 33 of 131 (25%) patients reported a VAS of 1-3 and the remaining 98 (75%) reported a VAS >3.
Clinical Utility
The ideal study would be a randomized controlled trial (RCT) comparing health outcomes after nTMS versus other strategies without nTMS in patients being considered for surgical resection of brain tumors. There are challenges in the design and interpretation of such studies.
A second study by this research group, with some overlap in enrolled patients, was published by Krieg and colleagues (Krieg, 2015).
This study prospectively enrolled 70 patients who underwent nTMS and matched them with a historical control group of 70 patients who did not have preoperative nTMS. All patients had motor eloquently located supratentorial high-grade gliomas (HGG) and they all underwent craniotomy in the single department by the same group of surgeons. As in the 2014 study by Krieg and colleagues, patients were matched by tumor location, preoperative paresis and histology, and the primary outcome was not specified. Outcome assessment was blinded. Craniotomy size was 25.3 cm2
(SD: 9.7cm) in the nTMS group and 30.8 cm2 (SD: 13.2) in the non-nTMS group; the difference in size was statistically significant, p=0.006. There was not a statistically significant difference between groups in the rate of surgery-related paresis, rate of surgery-related complications on MRI or the degree of motor impairment during follow-up. Median overall survival was 15.7 months (SD: 10.9) in the nTMS group and 11.9 months (SD: 10.3) in the non-nTMS group which was not significantly different between groups (p=0.131). Mean survival at 3, 6 and, 9 months was significantly higher in the nTMS group compared with the non-nTMS group and mean survival at 12 months did not differ significantly between groups.
One study used concurrent controls, but did not randomize patients to treatment group. Sollman and colleagues matched 25 prospectively enrolled patients who underwent preoperative nTMS but whose results were not available to the surgeon during the operation (group 1) to 25 patients who underwent preoperative nTMS and results were available to the surgeon (group 2) (Sollman, 2015).
All patients had language eloquently located brain lesions within the left hemisphere. Primary outcomes were not specified. Three months after surgery, 21 patients in group 1 had no or mild language impairment and 4 patients had moderate to severe language deficits. In group 2, 23 patients had no or mild language impairment and 2 patients had moderate to severe deficits. The difference between groups in post-operative language deficits was statistically significant (p=0.0153). Other outcomes, including duration of surgery, post-operative scores on the Karnofsky performance status scale, percent residual tumor, and peri- and postoperative complication rates did not differ significantly between groups.
Limitations of all of the studies discussed above in this section, include the single-center setting (because nTMS is an operator-dependent technology, applicability may be limited), lack of randomization and/or use of historical controls (surgeon technique and practice likely improved over time), selective outcome reporting (survival outcomes in glioma patients only), and uncertain validity of statistical analyses (primary outcome not identified and no correction for multiple testing). In addition, studies either matched patients to controls on a few variables or used controls who met similar eligibility criteria. These techniques may not adequately control for differences in patient groups that may affect outcomes.
For individuals who have brain lesions undergoing preoperative evaluation for localization of eloquent areas of the brain who receive navigated transcranial magnetic stimulation, the evidence includes controlled observational studies and case series. Relevant outcomes are overall survival, test accuracy, morbid events and functional outcomes. Several small studies have evaluated the distance between nTMS hotspots and direct cortical stimulation (DCS) hotspots for the same muscle. Although the average distance in most studies is 1 cm or less, this does not take into account the degree of error in this average distance, or whether there are missed hotspots. It is difficult to fully verify nTMS hotspots because only exposed cortical areas can be verified with DCS. Limited studies of nTMS to evaluate language areas show a high false positive rate (low specificity) and sensitivity that may be insufficient for clinical use.
Several controlled observational studies compared outcomes in patients undergoing nTMS versus other mapping techniques. Most outcomes were similar between groups, such as post-surgical motor impairment, paresis and surgical complication rates. Overall survival did not differ significantly between groups. One study found significantly higher mean survival rates in the nTMS group at 3, 6 and 9 months (but not 12 months) post-surgery. The controlled observational studies had various methodological limitations and, being non-randomized, may not adequately control for differences in patient groups that may affect outcomes. The evidence is insufficient to determine the effects of the technology on health outcomes.
2017 Update
A literature search was conducted using the MEDLINE database through November 2017. There was no information identified that would prompt a change in the coverage statement.
2018 Update
A literature search was conducted through October 2018. There was no new information identified that would prompt a change in the coverage statement.
2019 Update
Annual policy review completed with a literature search using the MEDLINE database through October 2019. No new literature was identified that would prompt a change in the coverage statement.
2020 Update
Annual policy review completed with a literature search using the MEDLINE database through October 2020. No new literature was identified that would prompt a change in the coverage statement.
2021 Update
Annual policy review completed with a literature search using the MEDLINE database through October 2021. No new literature was identified that would prompt a change in the coverage statement. The key identified literature is summarized below.
Jeltema et al published a systematic review of articles that compared nTMS to intraoperative DCS for mapping of motor or language function (Jeltema, 2020). Among 8 articles which evaluated mapping language function, sensitivity ranged from 10 to 100% and specificity ranged from 13.3 to 98% when nTMS was compared to DCS. The positive predictive value (PPV) ranged from 17 to 75% and the negative predictive value ranged from 57 to 100%.
Raffa et al (2019) published a systematic review and meta-analysis of observational studies in patients with motor-eloquent brain tumors who underwent presurgical nTMS motor mapping compared to patients without nTMS (Raffa, 2019). Eight observational studies with 1031 patients were included in the analysis (n=593 with preoperative nTMS mapping and n=438 without nTMS mapping). Included patients had low and high grade gliomas, glioblastoma, brain metastasis, vascular malformations, and cavernous and artero-venous malformations. In pooled analyses, use of nTMS was associated with a lower risk of postoperative new permanent motor deficits (odds ratio, 0.54; 95% confidence interval, 0.37 to 0.79; p =.001), a higher probability of achieving the gross total resection rate (removal of 100% of tumor tissue at early postoperative magnetic resonance scan) (odds ratio, 2.32; 95% confidence interval, 1.73 to 3.1; p <.001), and reduced craniotomy size (-6.24 cm2; p <.001). Length of surgery was non-significantly lower with nTMS (-10.3 minutes; P =.38).
2022 Update
Annual policy review completed with a literature search using the MEDLINE database through October 2022. No new literature was identified that would prompt a change in the coverage statement.
2023 Update
Annual policy review completed with a literature search using the MEDLINE database through October 2023. No new literature was identified that would prompt a change in the coverage statement. The key identified literature is summarized below.
A retrospective cohort study evaluated pediatric and adult patients with epilepsy or brain tumor who underwent TMS language mapping and functional MRI language mapping as part of a presurgical evaluation (Schiller, 2020).
There were 106patients with complete TMS language maps that were identified; of those patients, 84 also underwent functional MRI language mapping. The overall accuracy of TMS across all language areas when compared to functional MRI was 71% (which was mainly due to its high specificity of 83%), with a diagnostic odds ratio of 1.27; TMS was more accurate in determining the dominant hemisphere for language as well (diagnostic OR, 6). TMS was able to reliably localize cortical areas that are not essential for speech function, however, TMS demonstrated only slight concordance between TMS and functional MRI-derived language areas, which demonstrated low accuracy in localization of specific language cortices.
Observational Studies and Case Series
Most studies of nTMS are small case series or cohort studies evaluating patients with brain tumors, cavernous angiomas, arteriovenous malformations, gliomas (Baro and Ille), or other brain lesions; case series are not ideal studies to ascertain diagnostic characteristics. A number of small nTMS studies have also evaluated healthy volunteers but they do not add substantially to the evidence base (Schramm, 2019). Studies comparing nTMS with DCS, MEG, and/or fMRI and/or using DCS as the reference standard are described next.
2024 Update
Annual policy review completed with a literature search using the MEDLINE database through June 2024. No new literature was identified that would prompt a change in the coverage statement.
2025 Update
Annual policy review completed with a literature search using the MEDLINE database through June 2025. No new literature was identified that would prompt a change in the coverage statement.
2026 Update
Annual policy review completed with a literature search using the MEDLINE database through June 2026. No new literature was identified that would prompt a change in the coverage statement.
Additional 2026 Update
Annual policy review completed with a literature search using the MEDLINE database through August 2026. No new literature was identified that would prompt a change in the coverage statement. The key identified literature is summarized below.
Raffa et al conducted a meta-analysis evaluating the impact of nTMS-based motor mapping on surgery of motor-eloquent brain tumors (Raffa, 2019). Eight studies comparing nTMS-guided surgery to surgery without nTMS were included. The pooled analysis showed that nTMS motor mapping significantly reduced the risk of new permanent motor deficits (Odds Ratio [OR], 0.54; p=.001) and increased the gross total resection rate (OR, 2.32; p less than .001). Craniotomy size was reduced by 6.24 cm2 (p less than .001) in the nTMS group.
Indharty et al conducted a meta-analysis comparing nTMS with direct cortical stimulation in brain tumor surgery (Indharty, 2023). Fourteen comparative studies from 2010 to 2023 were included, comprising 1011 patients undergoing nTMS-based mapping and 732 patients undergoing DCS-based mapping. Outcomes included postoperative motor deficits or paresis and language deficits or aphasia. For motor outcomes, nTMS was not significantly different from DCS (Risk Ratio [RR], 0.85; 95% Confidence Interval [CI], 0.53 to 1.36; p=.50).
Primary motor-mapping studies included 19 comparative studies after excluding studies with less than 20 participants and noncomparative studies. These included 8 technical-validation studies, 10 clinical outcome studies comparing nTMS-informed surgery with no-nTMS, historical, matched, or intraoperative only mapping controls, and 1 motor-deficit prediction study comparing nTMS-seeded with functional magnetic resonance imaging (fMRI)-seeded tractography. Patients were generally adults with lesions in or near motor cortex or corticospinal pathways, including glioma, glioblastoma/high-grade glioma, metastasis, cavernoma, meningioma, arteriovenous malformation, and mixed supratentorial motor-eloquent lesions. Individual study sample sizes ranged from 20 to 365 patients, with clinical outcome cohorts generally larger than the same-patient validation cohorts.
In mapping-validation studies, nTMS generally showed spatial concordance with intraoperative direct cortical stimulation (DCS)/direct electrical stimulation (DES). Six studies reported nTMS to DCS/DES distance outcomes, with reported distances ranging from approximately 2.13 mm to 11.4 mm (Picht, 2011; Krieg, 2012; Tarapore, 2012; Jung, 2019; Weiss Lucas, 2020, Paiva, 2024). Studies comparing nTMS with other noninvasive modalities generally favored nTMS over fMRI or magnetoencephalography (MEG) for motor localization: Krieg et al reported larger nTMS-to-fMRI deviations than nTMS-to-DCS deviations, Tarapore et al reported larger MEG-to-DCS than nTMS-to-DCS distances, and Weiss Lucas et al reported smaller nTMS-to-DCS than fMRI-to-DCS distances and greater nTMS-DCS overlap (Krieg, 2012; Tarapore, 2012; Weiss Lucas, 2020). Coburger et al also reported better feasibility for nTMS than fMRI, while Conti et al found greater overlap between nTMS-seeded corticospinal tract diffusion tensor imaging (DTI) tractography and motor cortex than standard DTI tractography (Coburger, 2013; Conti, 2014).
In clinical outcome studies, resection-related outcomes generally favored nTMS-informed planning. Five studies reported explicit GTR rates (Frey, 2014; Picht, 2016; Raffa, 2019; Hendrix, 2021; Weiss Lucas, 2022). Across those studies, GTR ranged from approximately 59% to 81.9% in nTMS groups versus 42% to 69.5% in comparator groups. Three studies reported residual tumor rates, which ranged from 7.7% to 34.3% with nTMS versus 21.6% to 54.3% in controls. Three studies reported unexpected residual tumor, ranging from 3.4% to 15.7% with nTMS versus 18.4% to 32.9% in controls (Krieg, 2014; Krieg, 2015; Krieg, 2017). Additional volumetric resection outcomes were reported, including lower residual volume, greater degree of resection, or more favorable tumor-volume change with nTMS-informed strategies (Picht, 2013; Picht, 2016; Raffa, 2019; Weiss Lucas, 2022).
Motor function outcomes were less consistent than resection outcomes. Nine clinical outcome studies reported postoperative motor deficit, paresis, or motor worsening outcomes (Frey, 2014; Krieg, 2014; Krieg, 2014; Krieg, 2016; Picht, 2016; Raffa, 2018; Hendrix, 2021; Weiss Lucas, 2022). Across these studies, permanent or long-term motor deficit/worsening rates in nTMS groups ranged approximately from 2.9% to 17.1%, depending on whether nTMS alone or nTMS+DTI-fiber tracking subgroups were reported. Comparator-group rates ranged from 0% to 29.3%.
Operational outcomes favored nTMS in some but not all studies. Three studies reported numeric craniotomy-size, with mean craniotomy size ranging from approximately 22.4 to 25.3 cm2 in nTMS groups versus 26.7 to 32.0 cm2 in controls (Krieg, 2014; Krieg, 2015; Raffa, 2017)., Survival or PFS outcomes were reported in several studies but these outcomes were heterogeneous and confounded by tumor type, treatment era, radiotherapy/chemotherapy differences, extent of resection, and multimodal surgical strategy (Frey, 2014; Krieg, 2015; Hendrix, 2021; Weiss Lucas, 2022).
Safety reporting was inconsistent and generally not systematic. Across the mapping studies, nTMS was usually described as tolerated with few or no attributed serious adverse events to nTMS (Picht, 2013; Coburger, 2013; Conti, 2014; Krieg, 2014; Krieg, 2014). Reported nTMS tolerability events included unpleasantness without pain in some patients. In contrast, intraoperative stimulation and surgery carried expected risks: Paiva et al reported DES seizure activity in 16.6% of procedures and surgical complications in 10%, while Raffa et al reported postoperative seizures of 17.1% with nTMS, 14.3% with nTMS+DTI-FT, and 40% in controls (Paiva, 2024; Raffa, 2018). Several clinical studies reported postoperative complications, infections, hemorrhage, revision, or neurologic worsening, but attribution to nTMS itself was usually not possible because nTMS was embedded in broader surgical workflows.
Two systematic reviews were identified. Jeltema et al found broad variability across language mapping studies (Jeltema, 2021). All language-mapping studies used Nexstim systems and object-naming tasks. Compared with direct cortical stimulation (DCS), sensitivity ranged from 10% to 100%, specificity from 13.3% to 98%, positive predictive value (PPV) from 17% to 75%, and negative predictive value (NPV) from 57% to 100%. No adverse events were mentioned in the language-mapping studies, and pediatric language mapping was reported as well tolerated in 1 included study. Indharty et al also compared TMS with direct cortical stimulation in brain tumor surgery and included mixed motoric and lingual outcomes (Indharty, 2023). The review reported no significant differences between of nTMS and DCS for lingual outcomes (Risk ratio, 1.32; 95% CI, 0.79 to 2.2).
Primary language-mapping evidence included 9 retained studies with approximately 527 patients. These included 4 mapping-validation studies comparing nTMS with direct cortical stimulation (DCS), functional magnetic resonance imaging (fMRI), or intraoperative speech arrest (N=140), 3 comparative clinical/workflow studies evaluating maps-available, historical-control, or awake-direct electrical stimulation (DES) comparator workflows (N=237) (Picht, 2013; Ille, 2015; Muir, 2022; Jung, 2025; Sollmann, 2015; Hendrix, 2017; Ille, 2021). Patients were generally adults with left-sided, dominant-hemisphere, perisylvian, or language-eloquent gliomas or mixed language-eloquent lesions; reported mean ages ranged from the mid-40s to 60s, and cohorts included glioblastoma multiforme, anaplastic astrocytoma, diffuse astrocytoma, low-grade glioma, metastasis, cavernoma, and other lesions.
In the diagnostic-validation studies, 3 studies reported conventional nTMS diagnostic performance against DCS using sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) (Picht, 2013; Ille, 2015; Muir, 2022). Across these studies, nTMS sensitivity generally ranged from approximately 83% to 91%, specificity from 24% to 67%, PPV from 16% to 36%, and NPV from 84% to 99%, depending on task, threshold, and analysis unit. The most consistent signal was high NPV/rule-out value, while specificity and PPV were low or variable, limiting confidence in positive nTMS language sites as definitive markers of essential cortex. Picht et al reported overall sensitivity 90%, specificity 24%, PPV 36%, and NPV 84%; Muir et al reported TMS sensitivity 83% to 87%, specificity 67%, PPV 16%, and NPV 99% compared with DCS (Picht, 2013; Muir, 2022).
Ille et al compared nTMS and fMRI with DCS and showed that diagnostic performance depended heavily on the nTMS threshold/protocol (Ille, 2015). For rTMS using a picture to trigger interval (PTI) of 0 ms and the 2-out-of-3 error classification rule, PPV was 30%, NPV 97%, sensitivity 91%, and specificity 56%. Combined nTMS+fMRI protocols produced different tradeoffs rather than one unified classifier: the AND-type protocol had PPV 51%, NPV 76%, sensitivity 41%, and specificity 83%, while the OR-type protocol had PPV 34%, NPV 95%, sensitivity 98%, and specificity 13%. fMRI comparator data in Ille et al and Muir et al suggest that fMRI may be more specific in some settings but less sensitive, while nTMS generally provides stronger rule-out performance (Ille, 2015; Muir, 2022).
Three studies evaluated language outcomes using historical-control, or awake-DES comparator designs (Sollmann, 2015; Hendrix, 2017; Ille, 2021). Early postoperative language outcomes sometimes favored nTMS-informed workflows: Sollmann et al reported postoperative medium/severe language deficits of 16% when nTMS maps were available versus 48% when maps were unavailable (p=.0153), and Hendrix et al reported improvement of preoperative language deficit by postoperative day 5 to 7 in 57.1% of nTMS-guided cases versus 7.7% of historical controls (p=.013) (Sollmann, 2015; Hendrix, 2017). However, durable differences were not consistently shown: Sollmann et al reported follow-up medium/severe deficits of 8% versus 16% (p=.3841), and Hendrix et al found better language performance at 6 weeks but no significant difference at 3 months (Sollmann, 2015; Hendrix, 2017).
Resection-related outcomes were reported in 3 studies, but the endpoints varied. Two studies reported GTR rates: Hendrix et al reported 65% GTR in both nTMS and historical-control groups, while Ille et al reported GTR 87% in the nTMS asleep-surgery group versus 72% in the awake-DES group (p=.04) (Hendrix, 2017; Ille, 2021). Sollmann et al reported unexpected residual tumor of 16% with maps available versus 32% with maps unavailable (p=.1853), as well as smaller craniotomy measures when nTMS maps were available: anterior-posterior craniotomy extent 6.5 +/- 1.3 cm versus 7.5 +/- 1.4 cm (p=.0117) and craniotomy size 41.6 +/- 10.4 cm2 versus 50.1 +/- 16.8 cm2 (p=.0373). These results suggest possible workflow and surgical-planning benefit, but they are not consistent evidence of durable language benefit.
Postoperative language morbidity varied widely across cohorts and was difficult to pool because studies used different definitions and follow-up intervals. In Ille et al, across 147 language-eloquent glioma cases, no new postoperative language deficit occurred in 67.3%, transient new deficit in 21.8%, permanent new deficit in 4.1%, and 6.8% were not assessable because of decreased vigilance (Ille, 2021) In Muir et al, a high-risk diagnostic-validation cohort, transient worsened postoperative aphasia occurred in 17/28 (61%), and worsened aphasia beyond 30 days occurred in 9/24 (38%) with available follow-up (Muir, 2022).
Two studies evaluated nTMS-seeded language tractography or multimodal tractography for predicting permanent or long-term aphasic decline. Muir et al reported that resection of cortical nTMS points alone did not predict permanent language deficits (Muir, 2025). Patient-specific colocalization of nTMS tracts with normative language-associated tracts predicted permanent deficits with 94% accuracy, 80% sensitivity, 97% specificity, 80% PPV, and 97% NPV. Muir et al reported that resection of nTMS-seeded tracts predicted long-term aphasic decline at 50% normalized fractional anisotropy (FA) (OR, 11; 95% CI, 1.31 to 92.35; p=.027) and 75% normalized FA (OR, 51; 95% CI, 3.25 to 492.92; p less than .001), while fMRI-seeded tracts did not predict outcomes at any FA threshold (Muir, 2026). Across these 2 studies, TMS-tractography sensitivity ranged from 80% to 90%, specificity from 85% to 97%, PPV from 50% to 80%, and NPV from 97% to 98%.
Safety reporting was limited and inconsistent. Picht et al reported no adverse events related to nTMS speech mapping, although DCS-induced seizures occurred in 2 patients during awake intraoperative mapping and were terminated intraoperatively (Picht, 2013). Sollmann et al reported no nTMS adverse events (Sollmann, 2015). Hendrix et al reported perioperative complications in 3 (15%) nTMS patients versus 2 (10%) controls (p=1.0), but these were surgical complications rather than clearly nTMS-related events (Hendrix, 2017). Jung et al reported postoperative hemorrhage, ischemic stroke, and infection requiring return to theatre, each in 1/57 (2%); again, these were perioperative/surgical events rather than nTMS-specific safety signals (Jung, 2025).
The International Federation of Clinical Neurophysiology published an updated committee report on the clinical diagnostic utility of nTMS in neurologic disorders in 2023 (Vucic, 2023). The report describes nTMS as a diagnostic and monitoring technique in neurologic disease and states that TMS can be used to perform functional mapping of eloquent brain regions during preoperative assessment before surgical resection of brain tumors. This guidance supports the clinical role of TMS as a preoperative functional mapping modality but does not provide Nexstim-specific coverage criteria or evidence-graded recommendations for motor versus language mapping.
The NCCN Guidelines for Central Nervous System Cancers discuss preoperative functional MRI and/or diffusion tensor imaging fiber tracking, awake craniotomy, and motor and/or speech mapping as surgical adjuncts that may facilitate safe brain tumor surgery (NCCN, 2026). The guidelines describe fMRI as a noninvasive pre-treatment tool for evaluating eloquent brain regions in relation to tumors, while noting limitations related to patient task performance and availability of specialized expertise. The guidelines do not specifically address navigated transcranial magnetic stimulation for presurgical mapping.
Some currently ongoing and unpublished trials that might influence this review are listed below.
Ongoing
Unpublished
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