Intraoperative neurophysiologic mapping of the central cortical region for epidural electrode placement in the treatment of neuropathic pain by motor cortex stimulation

Targeting Lower Limb, Upper Limb, and Face Representation in the Primary Motor Cortex for the Practice of Neuronavigated Transcranial Magnetic Stimulation

OBJECTIVE

The primary motor cortex (M1) is a usual target for therapeutic application of repetitive transcranial magnetic stimulation (rTMS), especially the region of hand motor representation. However, other M1 regions can be considered as potential rTMS targets, such as the region of lower limb or face representation. In this study, we assessed the localization of all these regions on magnetic resonance imaging (MRI) with the aim of defining three standardized M1 targets for the practice of neuronavigated rTMS.

MATERIALS AND METHODS

A pointing task of these targets was performed by three rTMS experts on 44 healthy brain MRI data to assess interrater reliability (including the calculation of intraclass correlation coefficients [ICCs] and coefficients of variation [CoVs] and the construction of Bland-Altman plots). In addition, two "standard" brain MRI data were randomly interspersed with the other MRI data to assess intrarater reliability. A barycenter was calculated for each target (with x-y-z coordinates provided in normalized brain coordinate systems), in addition to the geodesic distance between the scalp projection of the barycenters of these different targets.

RESULTS

Intrarater and interrater agreement was good, according to ICCs, CoVs, or Bland-Altman plots, although interrater variability was greater for anteroposterior (y) and craniocaudal (z) coordinates, especially for the face target. The scalp projection of the barycenters between the different cortical targets ranged from 32.4 to 35.5 mm for either the lower-limb-to-upper-limb target distance or the upper-limb-to-face target distance.

CONCLUSIONS

This work clearly delineates three different targets for the application of motor cortex rTMS that correspond to lower limb, upper limb, and face motor representations. These three targets are sufficiently spaced to consider that their stimulation can act on distinct neural networks.

Positioning of epidural electrode for motor cortex stimulation in general anesthesia based on intraoperative electrophysiological monitoring to treat refractory trigeminal neuropathic pain

BACKGROUND

Motor cortex stimulation (MCS) represents a treatment option for refractory trigeminal neuralgia (TGN). Usually, patients need to be awake during surgery to confirm a correct position of the epidural electrode above the motor cortex, reducing patient's comfort.

METHOD

Epidural cortical mapping (ECM) and motor evoked potentials (MEPs) were intraoperatively performed for correct localization of motor cortex under general anesthesia that provided comparable results to test stimulation after letting the patient to be awake during the operation.

CONCLUSION

Intraoperative ECM and MEPs facilitate a confirmation of correct MCS-electrode position above the motor cortex allowing the MCS-procedure to be performed under general anesthesia.

Motor Evoked Potential Warning Criteria in Supratentorial Surgery: A Scoping Review

During intraoperative monitoring of motor evoked potentials (MEP), heterogeneity across studies in terms of study populations, intraoperative settings, applied warning criteria, and outcome reporting exists. A scoping review of MEP warning criteria in supratentorial surgery was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sixty-eight studies fulfilled the eligibility criteria. The most commonly used alarm criteria were MEP signal loss, which was always a major warning sign, followed by amplitude reduction and threshold elevation. Irreversible MEP alterations were associated with a higher number of transient and persisting motor deficits compared with the reversible changes. In almost all studies, specificity and Negative Predictive Value (NPV) were high, while in most of them, sensitivity and Positive Predictive Value (PPV) were rather low or modest. Thus, the absence of an irreversible alteration may reassure the neurosurgeon that the patient will not suffer a motor deficit in the short-term and long-term follow-up. Further, MEPs perform well as surrogate markers, and reversible MEP deteriorations after successful intervention indicate motor function preservation postoperatively. However, in future studies, a consensus regarding the definitions of MEP alteration, critical duration of alterations, and outcome reporting should be determined.

Non pharmacological treatment for neuropathic pain: Invasive and non-invasive cortical stimulation

The use of medications in chronic neuropathic pain may be limited with regard to efficacy and tolerance. Therefore, non-pharmacological approaches, using electrical stimulation of the cortex has been proposed as an alternative. First, in the early nineties, surgically-implanted epidural motor cortex stimulation (EMCS) was proven to be effective to relieve refractory neuropathic pain. Later, non-invasive stimulation techniques were found to produce similar analgesic effects, at least by means of repetitive transcranial magnetic stimulation (rTMS) targeting the primary motor cortex (M1). Following "high-frequency" rTMS (e.g., stimulation frequency ranging from 5 to 20Hz) delivered to the precentral gyrus (e.g., M1 region), it is possible to obtain an analgesic effect via the modulation of several remote brain regions involved in nociceptive information processing or control. This pain reduction can last for weeks beyond the time of the stimulation, especially if repeated sessions are performed, probably related to processes of long-term synaptic plasticity. Transcranial direct current stimulation (tDCS), another form of transcranial stimulation, using low-intensity electrical currents, generally delivered by a pair of large electrodes, has also shown some efficacy to improve patients with chronic pain syndromes. The mechanism of action of tDCS differs from that of EMCS and rTMS, but the cortical target is the same, which is M1. Although the level of evidence of therapeutic efficacy in the context of neuropathic pain is lower for tDCS than for rTMS, interesting perspectives are opened by using at-home tDCS protocols for long-term management. Now, there is a scientific basis for recommending both EMCS and rTMS of M1 to treat refractory chronic neuropathic pain, but their application in clinical practice remains limited due to practical and regulatory issues.

Motor Cortex Stimulation for Deafferentation Pain

PURPOSE OF REVIEW

Since the early 1990s, motor cortex stimulation (MCS) has been a unique treatment modality for patients with drug-resistant deafferentation pain. While underpowered studies and case reports have limited definitive, data-driven analysis of MCS in the past, recent research has brought new clarity to the MCS literature and has helped identify appropriate indications for MCS and its long-term efficacy.

RECENT FINDINGS

In this review, new research in MCS, repetitive transcranial magnetic stimulation (rTMS), and transcranial direct current stimulation (tDCS) are analyzed and compared with historical landmark papers. Currently, MCS is effective in providing relief to 40-64% of patients, with decreasing analgesic effect over time addressed by altering stimulation settings. rTMS and tDCS, two historic, non-invasive stimulation techniques, are providing new alternatives for the treatment of deafferentation pain, with rTMS finding utility in identifying MCS responders. Future advances in electrode arrays, neuro-navigation, and high-definition tDCS hold promise in providing pain relief to growing numbers of patients. Deafferentation pain is severe, disabling, and remains a challenge for patients and providers alike. Over the last several years, the MCS literature has been revitalized with studies and meta-analyses demonstrating MCS effectiveness and providing guidance in identifying responders. At the same time, rTMS and tDCS, two time-honored non-invasive stimulation techniques, are finding new utility in managing deafferentation pain and identifying good MCS candidates. As the number of potential therapies grow, the clinician's role is shifting to personalizing treatment to the unique pain of each patient. With new treatment modalities, this form of personalized medicine is more possible than ever before.

Cortical neurostimulation for neuropathic pain: state of the art and perspectives

The treatment of neuropathic pain by neuromodulation is an objective for more than 40 years in modern clinical practice. With respect to spinal cord and deep brain structures, the cerebral cortex is the most recently evaluated target of invasive neuromodulation therapy for pain. In the early 90s, the first successes of invasive epidural motor cortex stimulation (EMCS) were published. A few years later was developed repetitive transcranial magnetic stimulation (rTMS), a noninvasive stimulation technique. Then, electrical transcranial stimulation returned valid and is currently in full development, with transcranial direct current stimulation (tDCS). Regarding transcranial approaches, the main studied and validated target was still the motor cortex, but other cortical targets are under investigation. The mechanisms of action of these techniques share similarities, especially between EMCS and rTMS, but they also have differences that could justify specific indications and applications. It is therefore important to know the principles and to assess the merit of these techniques on the basis of a rigorous assessment of the results, to avoid fad. Various types of chronic neuropathic pain syndromes can be significantly relieved by EMCS or repeated daily sessions of high-frequency (5-20 Hz) rTMS or anodal tDCS over weeks, at least when pain is lateralized and stimulation is applied to the motor cortex contralateral to pain side. However, cortical stimulation therapy remains to be optimized, especially by improving EMCS electrode design, rTMS targeting, or tDCS montage, to reduce the rate of nonresponders, who do not experience clinically relevant effects of these techniques.

Motor Cortex Stimulation for Neuropathic Pain: A Randomized Cross-over Trial

BACKGROUND

Chronic motor cortex stimulation (MCS) has been used to treat medically refractory neuropathic pain over the past 20 years. We investigated this procedure using a prospective multicentre randomized blinded crossover trial.

METHODS

Twelve subjects with three different neuropathic pain syndromes had placement of MCS systems after which they were randomized to receive low ("subtherapeutic") or high ("therapeutic") stimulation for 12 weeks, followed by a crossover to the other treatment group for 12 weeks. The primary outcome measure was the pain visual analogue scale (VAS). Secondary outcome measures included McGill Pain Questionnaire (MPQ), Beck Depression Inventory-II, medication log, work status, global impression of change, and SF-36 quality of life scale.

RESULTS

The trial was halted early due to lack of efficacy. One subject withdrew early due to protocol violation and five subjects withdrew early due to transient adverse events. Six subjects with upper extremity pain completed the study. There was no significant change in VAS with low or high stimulation and no significant improvement in any of the outcome measures from low to high stimulation. SF-36 role physical and mental health scores were worse with high compared to low stimulation (p=0.024, p=0.005).

CONCLUSIONS

We failed to show that MCS is an effective treatment for refractory upper extremity neuropathic pain and suggest that previous studies may have been skewed by placebo effects, or ours by nocebo. We suggest that a healthy degree of skepticism is warranted when considering this invasive therapy for upper extremity pain syndromes.

Neuropathic pain: transcranial electric motor cortex stimulation using high frequency random noise. Case report of a novel treatment

Objectives

Electric motor cortex stimulation has been reported to be effective for many cases of neuropathic pain, in the form of epidural stimulation or transcranial direct current stimulation (tDCS). A novel technique is transcranial random noise stimulation (tRNS), which increases the cortical excitability irrespective of the orientation of the current. The aim of this study was to investigate the effect of tRNS on neuropathic pain in a small number of subjects, and in a case study explore the effects of different stimulation parameters and the long-term stability of treatment effects.

Methods

The study was divided into three phases: (1) a double-blind crossover study, with four subjects; (2) a double-blind extended case study with one responder; and (3) open continued treatment. The motor cortex stimulation consisted of alternating current random noise (100–600 Hz), varying from 0.5 to 10 minutes and from 50 to 1500 μA, at intervals ranging from daily to fortnightly.

Results

One out of four participants showed a strong positive effect (also compared with direct-current-sham, P = 0.006). Unexpectedly, this effect was shown to occur also for very weak (100 μA, P = 0.048) and brief (0.5 minutes, P = 0.028) stimulation. The effect was largest during the first month, but remained at a highly motivating level for the patient after 6 months.

Discussion

The study suggests that tRNS may be an effective treatment for some cases of neuropathic pain. An important result was the indication that even low levels of stimulation may have substantial effects.

Pain

Invasive stimulation of the motor (precentral) cortex using surgically implanted epidural electrodes is indicated for the treatment of neuropathic pain that is refractory to medical treatment. Controlled trials have demonstrated the efficacy of epidural motor cortex stimulation (MCS), but MCS outcome remains variable and validated criteria for selecting good candidates for implantation are lacking. Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive approach that could be used as a preoperative tool to predict MCS outcome and also could serve as a therapeutic procedure in itself to treat pain disorders. This requires repeated rTMS sessions and a maintenance protocol. Other studies have also demonstrated the efficacy of transcranial direct current stimulation (tDCS) in relieving chronic pain syndromes. The most studied target is the precentral cortex, but other targets, such as the prefrontal and parietal cortices, could be of interest. The analgesic effects of cortical stimulation relate to the activation of various circuits modulating neural activities in remote structures, such as the thalamus, limbic cortex, insula, or descending inhibitory controls. In addition to the treatment of refractory neuropathic pain by epidural MCS, new developments of this type of strategy are ongoing, for other types of pain syndrome and stimulation techniques.

Coupling BCI and cortical stimulation for brain-state-dependent stimulation: methods for spectral estimation in the presence of stimulation after-effects

Brain-state-dependent stimulation (BSDS) combines brain-computer interfaces (BCIs) and cortical stimulation into one paradigm that allows the online decoding for example of movement intention from brain signals while simultaneously applying stimulation. If the BCI decoding is performed by spectral features, stimulation after-effects such as artefacts and evoked activity present a challenge for a successful implementation of BSDS because they can impair the detection of targeted brain states. Therefore, efficient and robust methods are needed to minimize the influence of the stimulation-induced effects on spectral estimation without violating the real-time constraints of the BCI. In this work, we compared four methods for spectral estimation with autoregressive (AR) models in the presence of pulsed cortical stimulation. Using combined EEG-TMS (electroencephalography-transcranial magnetic stimulation) as well as combined electrocorticography (ECoG) and epidural electrical stimulation, three patients performed a motor task using a sensorimotor-rhythm BCI. Three stimulation paradigms were varied between sessions: (1) no stimulation, (2) single stimulation pulses applied independently (open-loop), or (3) coupled to the BCI output (closed-loop) such that stimulation was given only while an intention to move was detected using neural data. We found that removing the stimulation after-effects by linear interpolation can introduce a bias in the estimation of the spectral power of the sensorimotor rhythm, leading to an overestimation of decoding performance in the closed-loop setting. We propose the use of the Burg algorithm for segmented data to deal with stimulation after-effects. This work shows that the combination of BCIs controlled with spectral features and cortical stimulation in a closed-loop fashion is possible when the influence of stimulation after-effects on spectral estimation is minimized.

Motor cortex stimulation for facial chronic neuropathic pain: A review of the literature

Background:

Facial chronic neuropathic pain (FCNP) is a disabling clinical entity, its incidence is increasing within the chronic pain population. There is indication for neuromodulation when conservative treatment fails. Motor cortex stimulation (MCS) has emerged as an alternative in the advanced management of these patients. The aim of this work is to review the worldwide literature on MCS for FCNP.

Methods:

A PubMed search from 1990 to 2012 was conducted using established MeSH words. A total of 126 relevant articles on MCS focused on chronic pain were selected and analysed. Series of cases were divided in (1) series focused on MCS for FCNP, and (2) MCS series of FCNP mixed with other chronic pain entities.

Results:

A total of 118 patients have been trialed for MCS for FCNP, 100 (84.7%) pursued permanent implantation of the system, and 84% of them had good pain control at the end of the study. Male: female ratio was about 1:2 in the whole group of studies; mean age was 58 years (range, 28–83), and mean pain duration was 7 years (range, 0.6–25). Four randomized controlled studies have been reported, all of them not focused on MCS for FCNP. The most common complication was seizure followed by wound infection. Preoperative evaluation, surgical techniques, and final settings varied among the series.

Conclusion:

MCS for FNCP is a safe and efficacious treatment option when previous managements have failed; however, there is still lack of strong evidence (larger randomized controlled multicentre studies) that MCS can be offered in a regular basis to FNCP patients.

The emerging use of brain stimulation treatments for psychiatric disorders

OBJECTIVE

The aim of this study was to review the current state of development and application of a wide range of brain stimulation approaches in the treatment of psychiatric disorders.

METHOD

The approaches reviewed include forms of minimally invasive magnetic and electrical stimulation, seizure induction, implanted devices and several highly novel approaches in early development.

RESULTS

An extensive range of brain stimulation approaches are now being widely used in the treatment of patients with psychiatric disorders, or actively investigated for this use. Both vagal nerve stimulation (VNS) and repetitive transcranial magnetic stimulation (rTMS) have been introduced into clinical practice in some countries. A small body of research suggests that VNS has some potentially long-lasting antidepressant effects in a minority of patients treated. rTMS has now been extensively investigated for over 15 years, with a large body of research now supporting its antidepressant effects. Further rTMS research needs to focus on defining the most appropriate stimulation methods and exploring its longer term use in maintenance protocols. Very early data suggest that magnetic seizure therapy (MST) has promise in the treatment of patients referred for electroconvulsive therapy: MST appears to have fewer side effects and may have similar efficacy. A number of other approaches including surgical and alternative forms of electrical stimulation appear to alter brain activity in a promising manner, but are in need of evaluation in more substantive patient samples.

CONCLUSIONS

It appears likely that the range of psychiatric treatments available for patients will grow over the coming years to progressively include a number of novel brain stimulation techniques.

Predictive value of rTMS in the identification of responders to epidural motor cortex stimulation therapy for pain

This study was designed to assess the value of repetitive transcranial magnetic stimulation (rTMS) to predict the efficacy of epidural motor cortex stimulation (EMCS) to treat neuropathic pain. We have included 59 patients treated by EMCS for more than 1 year and in whom active and sham 10Hz-rTMS sessions were performed as preoperative tests, targeted over the cortical representation of the painful area. Analgesic effects were rated on a visual analogue scale. The real rTMS efficacy was determined by subtracting the effect of the sham stimulation on pain scores from that of the active stimulation (active-sham calculation). Pain scores were significantly reduced by active rTMS and EMCS, but not by sham rTMS. Twenty-six of the 33 patients (79%) who responded to active rTMS and all the 21 patients (100%) who responded for active-sham calculation also responded to EMCS. The response observed in active-sham calculation had a positive predictive value of 1.0, but a negative predictive value of .6 regarding EMCS outcome. The analgesic effect of rTMS or EMCS was not influenced by the side, origin, or duration of pain or by the presence of motor or sensory deficit in the painful area. Poorer results were observed in case of lower limb pain for rTMS and in older patients for EMCS. This study confirms that neuropathic pain can be significantly relieved by motor cortex rTMS or EMCS. A positive outcome of EMCS can be predicted by a real response to rTMS, but not on clinical grounds.

PERSPECTIVE

Single sessions of sham-controlled preoperative rTMS tests can be used to confirm the indication of EMCS therapy but have no value to exclude patients from this therapy. New rTMS protocols remain to be assessed to improve the usefulness of preoperative rTMS in EMCS practice.

Treatment of poststroke pain by epidural motor cortex stimulation with a new octopolar lead

BACKGROUND

Chronic, drug-resistant neuropathic pain can be treated by surgically implanted motor cortex stimulation (MCS). The leads used for MCS have not been specifically designed for this application.

OBJECTIVE

To study the value of a new 8-contact lead for MCS therapy in a series of 6 patients with refractory central poststroke pain.

METHODS

The study comprised a 1-month randomized phase, starting 1 month after implantation, during which the neurostimulator was switched on in one-half of the patients or remained off in the other half, followed by an open phase of 10 months, during which the stimulator was switched on in all patients. Clinical assessment was performed at baseline and 1, 2, 3, 6, and 12 months after implantation with the following scales: Visual Analog Scale, Verbal Rating Scale, Brief Pain Inventory, McGill Pain Questionnaire, Sickness Impact Profile, and Medication Quantification Scale.

RESULTS

In the randomized phase, clinical scores were found to be globally reduced in the on- vs off-stimulation condition. In the open follow-up phase, all clinical scores improved significantly over time. The ratio between affective and sensory McGill Pain Questionnaire subscores decreased, suggesting a preferential effect of MCS on the affective component of pain. Compared with preoperative baseline, 2 patients were totally relieved of central poststroke pain, 3 patients were very much relieved, and 1 patient remained unchanged at the final examination.

CONCLUSION

A good clinical outcome was observed in all patients except 1, suggesting that this new octopolar lead could be used for MCS therapy to treat refractory central poststroke pain.