Somatotopic effects of rTMS in neuropathic pain? A comparison between stimulation over hand and face motor areas

One session of repetitive transcranial magnetic stimulation induces mild and transient analgesic effects among female individuals with painful temporomandibular disorders

OBJECTIVE

Temporomandibular disorders (TMD) are characterised by chronic pain and dysfunction in the jaw joint and masticatory muscles. Repetitive transcranial magnetic stimulation (rTMS) has emerged as a potential non-invasive treatment for chronic pain; however, its effectiveness in individuals with TMD has not been thoroughly investigated. This study aimed to evaluate the immediate and sustained (over seven consecutive days) effects of a single session of active rTMS compared to sham stimulation on pain intensity and pain unpleasantness in individuals with TMD.

METHODS

A randomised, double-blind, sham-controlled trial enrolled 41 female participants with chronic TMD. Pain intensity and pain unpleasantness were assessed immediately pre- and post-intervention, as well as twice daily for 21 days using electronic diaries. Secondary outcomes included pain interference, sleep quality, positive and negative affect and pain catastrophizing. Adverse effects were monitored. Repeated measures ANOVA and multilevel modelling regression analyses were employed for data analysis.

RESULT

Active rTMS demonstrated a significant immediate mild reduction in pain intensity and pain unpleasantness compared to sham stimulation. However, these effects were not sustained over the 7-day post-intervention period. No significant differences were observed between interventions for pain interference, sleep quality and negative affect. A minority of participants reported minor and transient side effects, including headaches and fatigue.

CONCLUSION

A single session of active rTMS was safe and led to immediate mild analgesic effects in individuals with TMD compared to sham stimulation. However, no significant differences were observed between interventions over the 7-day post-intervention period. Based on this study, rTMS stimulation appears to be a promising safe approach to be tested in TMD patients with longer stimulation protocols.

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.

Research Trends and Hotspots of Neuromodulation in Neuropathic Pain: A Bibliometric Analysis

BACKGROUND

Neuropathic pain (NeuP), the result of a lesion or disease of the somatosensory nervous system, is tricky to cure clinically. Mounting researches reveal that neuromodulation can safely and effectively ameliorate NeuP. The number of publications associated with neuromodulation and NeuP increases with time. However, bibliometric analysis on the field is rare. The present study aims to analyze trends and topics in neuromodulation and NeuP research by using a bibliometric method.

METHODS

This study systematically collected the relevant publications on the Science Citation Index Expanded of Web of Science from January 1994 to January 17, 2023. CiteSpace software was used to draw and analyze corresponding visualization maps.

RESULTS

A total of 1404 publications were ultimately obtained under our specified inclusion criteria. The analysis showed that the focus of research on neuromodulation and NeuP had been developing steadily in recent years, with papers published in 58 countries/regions and 411 academic journals. The Journal of Neuromodulation and the author J.P. Lefaucheur published the most papers. The papers published in Harvard University and the United States contributed significantly. The cited keywords show that motor cortex stimulation, spinal cord stimulation, electrical stimulation, transcranial magnetic stimulation, and mechanism are the research hotspots in the field.

CONCLUSIONS

The bibliometric analysis showed that the number of publications on neuromodulation and NeuP are increasing rapidly, especially in the past 5 years. "Motor cortex stimulation," "electrical stimulation," "spinal cord stimulation," "transcranial magnetic stimulation" and "mechanism" catch the most attention among researchers in this field.

Beyond trial-and-error: Individualizing therapeutic transcranial neuromodulation for chronic pain

BACKGROUND AND OBJECTIVE

Repetitive transcranial magnetic stimulation (rTMS) applied to the motor cortex provides supplementary relief for some individuals with chronic pain who are refractory to pharmacological treatment. As rTMS slowly enters treatment guidelines for pain relief, its starts to be confronted with challenges long known to pharmacological approaches: efficacy at the group-level does not grant pain relief for a particular patient. In this review, we present and discuss a series of ongoing attempts to overcome this therapeutic challenge in a personalized medicine framework.

DATABASES AND DATA TREATMENT

Relevant scientific publications published in main databases such as PubMed and EMBASE from inception until March 2023 were systematically assessed, as well as a wide number of studies dedicated to the exploration of the mechanistic grounds of rTMS analgesic effects in humans, primates and rodents.

RESULTS

The main strategies reported to personalize cortical neuromodulation are: (i) the use of rTMS to predict individual response to implanted motor cortex stimulation; (ii) modifications of motor cortex stimulation patterns; (iii) stimulation of extra-motor targets; (iv) assessment of individual cortical networks and rhythms to personalize treatment; (v) deep sensory phenotyping; (vi) personalization of location, precision and intensity of motor rTMS. All approaches except (i) have so far low or moderate levels of evidence.

CONCLUSIONS

Although current evidence for most strategies under study remains at best moderate, the multiple mechanisms set up by cortical stimulation are an advantage over single-target 'clean' drugs, as they can influence multiple pathophysiologic paths and offer multiple possibilities of individualization.

SIGNIFICANCE

Non-invasive neuromodulation is on the verge of personalised medicine. Strategies ranging from integration of detailed clinical phenotyping into treatment design to advanced patient neurophysiological characterisation are being actively explored and creating a framework for actual individualisation of care.

Non-invasive cortical stimulation for drug-resistant pain

PURPOSE OF REVIEW

Neuromodulation techniques are being increasingly used to alleviate pain and enhance quality of life. Non-invasive cortical stimulation was originally intended to predict the efficacy of invasive (neurosurgical) techniques, but has now gained a place as an analgesic procedure in its own right.

RECENT FINDINGS

Repetitive transcranial magnetic stimulation (rTMS): Evidence from 14 randomised, placebo-controlled trials (~750 patients) supports a significant analgesic effect of high-frequency motor cortex rTMS in neuropathic pain. Dorsolateral frontal stimulation has not proven efficacious so far. The posterior operculo-insular cortex is an attractive target but evidence remains insufficient. Short-term efficacy can be achieved with NNT (numbers needed to treat) ~2-3, but long-lasting efficacy remains a challenge.Like rTMS, transcranial direct-current stimulation (tDCS) induces activity changes in distributed brain networks and can influence various aspects of pain. Lower cost relative to rTMS, few safety issues and availability of home-based protocols are practical advantages. The limited quality of many published reports lowers the level of evidence, which will remain uncertain until more prospective controlled studies are available.

SUMMARY

Both rTMS and tDCS act preferentially upon abnormal hyperexcitable states of pain, rather than acute or experimental pain. For both techniques, M1 appears to be the best target for chronic pain relief, and repeated sessions over relatively long periods of time may be required to obtain clinically significant benefits. Patients responsive to tDCS may differ from those improved by rTMS.

Application of Repetitive Transcranial Magnetic Stimulation in Neuropathic Pain: A Narrative Review

Neuropathic pain, affecting 6.9-10% of the general population, has a negative impact on patients' quality of life and potentially leads to functional impairment and disability. Repetitive transcranial magnetic stimulation (rTMS)-a safe, indirect and non-invasive technique-has been increasingly applied for treating neuropathic pain. The mechanism underlying rTMS is not yet well understood, and the analgesic effects of rTMS have been inconsistent with respect to different settings/parameters, causing insufficient evidence to determine its efficacy in patients with neuropathic pain. This narrative review aimed to provide an up-to-date overview of rTMS for treating neuropathic pain as well as to summarize the treatment protocols and related adverse effects from existing clinical trials. Current evidence supports the use of 10 Hz HF-rTMS of the primary motor cortex to reduce neuropathic pain, especially in patients with spinal cord injury, diabetic neuropathy and post-herpetic neuralgia. However, the lack of standardized protocols impedes the universal use of rTMS for neuropathic pain. rTMS was hypothesized to achieve analgesic effects by upregulating the pain threshold, inhibiting pain impulse, modulating the brain cortex, altering imbalanced functional connectivity, regulating neurotrophin and increasing endogenous opioid and anti-inflammatory cytokines. Further studies are warranted to explore the differences in the parameters/settings of rTMS for treating neuropathic pain due to different disease types.

Twenty-Three Months Repetitive Transcranial Magnetic Stimulation of the Primary Motor Cortex for Refractory Trigeminal Neuralgia: A Single-Case Study

Treatment refractory or recurrent trigeminal neuralgia (TN) is a severe chronic pain illness. Single-session repetitive transcranial magnetic stimulation (rTMS) has been shown to elicit analgesic effects in several craniofacial pain syndromes, including TN. However, the safety and long-term effect of multi-session rTMS for TN have yet to be fully explored. In this study, we present a case of a patient with medical treatment-refractory TN after microvascular decompression. The patient volunteered to undergo 73 sessions of 10 Hz rTMS over 23 months. Neurovagination was used for precise localization and stimulation of the hand and face representation at the left motor cortex. The numeric pain intensity scores derived using the visual analog scale served as a daily index of treatment efficacy. The patient experienced a significant weekly reduction in pain scores, cumulating in 70.89% overall pain relief. The medication dosages were reduced and then discontinued toward the end of the intervention period. No severe adverse events were reported. From our results, we can conclude that the longitudinal multi-session application of rTMS over the hand and face area of M1 is a safe and effective method for producing long-lasting pain relief in TN. Using rTMS may thus prove helpful as an adjunct to conventional methods for treating pain in TN.

The effect of theta burst stimulation over the primary motor cortex on experimental hamstring pain: A randomised, controlled study

Theta burst stimulation (TBS) over the primary motor cortex (M1) is an emerging technique that may have utility in the treatment of musculoskeletal pain. However, previous work exploring the analgesic effects of noninvasive brain stimulation has been limited largely to the arm or hand, despite 80% of acute musculoskeletal injuries occurring in the lower limb. This is a pertinent point, given the functional and neurophysiological differences between upper and lower limb musculature, as well as evidence suggesting that reorganization of corticomotor pathways is region-specific. This study investigated the effect of excitatory TBS on pain, function, and corticomotor organization during experimentally induced lower limb pain. Twenty-eight healthy participants attended 2 experimental sessions. On Day 0, participants completed 10 sets of 10 maximal eccentric contractions of the right hamstring muscles to induce delayed onset muscle soreness. Four consecutive blocks of either active or sham TBS were delivered on Day 2. Measures of mechanical sensitivity, pain (muscle soreness, pain intensity, pain area) function (single-leg hop distance, maximum voluntary isometric contraction, lower extremity functional scale), and corticomotor organization were recorded before and after TBS on Day 2. Pain and function were also assessed daily from Days 2 to 10. Active TBS reduced mechanical sensitivity compared to sham stimulation (P = .01). Corticomotor organization did not differ between groups, suggesting that improvements in mechanical sensitivity were not mediated by changes in M1. Subjective reports of pain intensity and function did not change following active TBS, contrasting previous reports in studies of the upper limb. PERSPECTIVE: M1 TBS reduces mechanical sensitivity associated with experimentally induced hamstring pain. Though further work is needed, these findings may hold important implications for those seeking to expedite recovery or reduce muscle sensitivity following hamstring injury.

Case report: The feasibility of rTMS with intrathecal baclofen pump for the treatment of unresolved neuropathic pain following spinal cord injury

The main objective of this study was to assess the efficacy and safety of 10 Hz repetitive transcranial magnetic stimulation (rTMS) for the treatment of unresolved neuropathic pain in an individual with spinal cord injury and an intrathecal baclofen pump. A 62-year-old male presented with drug resistant neuropathic pain as a result of a complete spinal cord lesion at T8 level. Pain was classified into four types: pressure pain in the left foot, burning pain in buttocks, burning pain in sternum, and electrical attacks in the trunk. The treatment period involved 6 weeks of rTMS stimulation performed 5 days per week, a 6-week follow up period with no stimulation, and an 8-week top up session period which began 5-weeks after the end of the follow up period. 2004 pulses were delivered at 10Hz over the right-hand representation of the left primary motor cortex at 80% resting motor threshold during each session. Assessments were based on the numerical rating scale (NRS), neuropathic pain scale (NPS), Hamilton Depression and Anxiety rating scales. Following the treatment period there was a 30, 13, and 29% reduction in sternum, buttocks, and left foot pain respectively, as reported by the NRS. During this time, electrical attacks were abolished following the third week of treatment. These changes corresponded to a 38% decrease in NPS scores and a 65 and 25% reduction in anxiety and depressions scores respectively. The changes in sternum, buttocks, and left foot pain reported on the NRS persisted for 1 week following treatment. Top up sessions delivered 11 weeks after the end of the treatment period were unsuccessful in reducing pain to the level achieved during the treatment period. A 13% reduction in NPS was seen during these 8-weeks. Anxiety and depression scores decreased 78 and 67% respectively. The frequency of electrical attacks was zero during this time. rTMS stimulation delivered throughout this study did not cause any interference with the functioning of the intrathecal baclofen pump. This case study illustrates that rTMS may be effective at reducing drug resistant neuropathic pain with certain pain types exhibiting greater propensity for change.

Repetitive Transcranial Magnetic Stimulation of the Primary Motor Cortex beyond Motor Rehabilitation: A Review of the Current Evidence

Transcranial magnetic stimulation (TMS) has emerged as a novel technique to stimulate the human brain through the scalp. Over the years, identifying the optimal brain region and stimulation parameters has been a subject of debate in the literature on therapeutic uses of repetitive TMS (rTMS). Nevertheless, the primary motor cortex (M1) has been a conventional target for rTMS to treat motor symptoms, such as hemiplegia and spasticity, as it controls the voluntary movement of the body. However, with an expanding knowledge base of the M1 cortical and subcortical connections, M1-rTMS has shown a therapeutic efficacy that goes beyond the conventional motor rehabilitation to involve pain, headache, fatigue, dysphagia, speech and voice impairments, sleep disorders, cognitive dysfunction, disorders of consciousness, anxiety, depression, and bladder dysfunction. In this review, we summarize the latest evidence on using M1-rTMS to treat non-motor symptoms of diverse etiologies and discuss the potential mechanistic rationale behind the management of each of these symptoms.

Analgesic Effects of Repetitive Transcranial Magnetic Stimulation at Different Stimulus Parameters for Neuropathic Pain: A Randomized Study

OBJECTIVES

The aim of the present study was to investigate the analgesic effects of repetitive transcranial magnetic stimulation over the primary motor cortex (M1-rTMS) using different stimulation parameters to explore the optimal stimulus condition for treating neuropathic pain.

MATERIALS AND METHODS

We conducted a randomized, blinded, crossover exploratory study. Four single sessions of M1-rTMS at different parameters were administered in random order. The tested stimulation conditions were as follows: 5-Hz with 500 pulses per session, 10-Hz with 500 pulses per session, 10-Hz with 2000 pulses per session, and sham stimulation. Analgesic effects were assessed by determining the visual analog scale (VAS) pain intensity score and Short-Form McGill Pain Questionnaire 2 (SF-MPQ2) score immediately before and immediately after intervention.

RESULTS

We enrolled 22 adults (age: 59.8 ± 12.1 years) with intractable neuropathic pain. Linear-effects models showed significant effects of the stimulation condition on changes in VAS pain intensity (p = 0.03) and SF-MPQ2 (p = 0.01). Tukey multiple comparison tests revealed that 10-Hz rTMS with 2000 pulses provided better pain relief than sham stimulation, with greater decreases in VAS pain intensity (p = 0.03) and SF-MPQ2 (p = 0.02).

CONCLUSIONS

The results of this study suggest that high-dose stimulation (specifically, 10-Hz rTMS at 2000 pulses) is more effective than lower-dose stimulation for treating neuropathic pain.

Prolonged Continuous Theta Burst Stimulation Can Regulate Sensitivity on Aβ Fibers: An Functional Near-Infrared Spectroscopy Study

Objective

High-frequency repetitive transcranial magnetic stimulation (rTMS) induces analgesic effects in both experimental pain and clinical pain conditions. However, whether rTMS can modulate sensory and pain thresholds on sensory fibers is still unclear. Here, we compared the effects of three rTMS paradigms on sensory and pain thresholds conducted by different sensory fibers (Aβ, Aδ, and C fibers) with sham stimulation and investigate the potential brain activation using functional near-infrared spectroscopy (fNIRS).

Methods

Forty right-handed healthy subjects were randomly allocated into one of four groups. Each subject received one session rTMS [prolonged continuous theta-burst stimulation (pcTBS), intermittent theta-burst stimulation (iTBS), 10 Hz rTMS or sham]. Current perception threshold (CPT), pain tolerance threshold (PTT), and fNIRS were measured at baseline, immediately after stimulation, and 1 h after stimulation, respectively.

Results

Significant differences between treatments were observed for changes for CPT 2,000 Hz between baseline and 1 h after rTMS (F = 6.551, P < 0.001): pcTBS versus sham (P = 0.004) and pcTBS versus 10 Hz rTMS (P = 0.007). There were significant difference in average HbO μm in the right frontopolar cortex (FPC) [channel 23: P = 0.030 (pcTBS versus sham: P = 0.036)], left dorsolateral prefrontal cortex (DLPFC) [channel 7: P = 0.006 (pcTBS versus sham: P = 0.004)], left FPC [channel 17: P = 0.014 (pcTBS versus sham: P = 0.046), channel 22: P = 0.004 (pcTBS versus sham: P = 0.004)] comparing four group in 1 h after stimulation in PTT 2000 Hz (Aβ-fiber).

Conclusion

Prolonged continuous theta-burst stimulation can regulate sensitivity on Aβ fibers. In addition, single-session pcTBS placed on left M1 can increase the excitability of DLPFC and FPC, indicating the interaction between M1 and prefrontal cortex may be a potential mechanism of analgesic effect of rTMS. Studies in patients with central post-stroke pain are required to confirm the potential clinical applications of pcTBS.

Cortical stimulation for chronic pain: from anecdote to evidence

Epidural stimulation of the motor cortex (eMCS) was devised in the 1990's, and has now largely supplanted thalamic stimulation for neuropathic pain relief. Its mechanisms of action involve activation of multiple cortico-subcortical areas initiated in the thalamus, with involvement of endogenous opioids and descending inhibition toward the spinal cord. Evidence for clinical efficacy is now supported by at least seven RCTs; benefits may persist up to 10 years, and can be reasonably predicted by preoperative use of non-invasive repetitive magnetic stimulation (rTMS). rTMS first developed as a means of predicting the efficacy of epidural procedures, then as an analgesic method on its own right. Reasonable evidence from at least six well-conducted RCTs favors a significant analgesic effect of high-frequency rTMS of the motor cortex in neuropathic pain (NP), and less consistently in widespread/fibromyalgic pain. Stimulation of the dorsolateral frontal cortex (DLPFC) has not proven efficacious for pain, so far. The posterior operculo-insular cortex is a new and attractive target but evidence remains inconsistent. Transcranial direct current stimulation (tDCS) is applied upon similar targets as rTMS and eMCS; it does not elicit action potentials but modulates the neuronal resting membrane state. tDCS presents practical advantages including low cost, few safety issues, and possibility of home-based protocols; however, the limited quality of most published reports entails a low level of evidence. Patients responsive to tDCS may differ from those improved by rTMS, and in both cases repeated sessions over a long time may be required to achieve clinically significant relief. Both invasive and non-invasive procedures exert their effects through multiple distributed brain networks influencing the sensory, affective and cognitive aspects of chronic pain. Their effects are mainly exerted upon abnormally sensitized pathways, rather than on acute physiological pain. Extending the duration of long-term benefits remains a challenge, for which different strategies are discussed in this review.

Efficacy and tolerability in patients with chronic facial pain of two consecutive treatment periods of rTMS applied over the facial motor cortex, using protocols differing in stimulation frequency, duration, and train pattern

OBJECTIVE

We conducted an open-label cross-over study assessing the global effect of two high-frequency protocols of electric-field navigated repetitive transcranial magnetic stimulation (rTMS) targeted to functional facial motor cortex and comparing their efficacy and tolerability in patients with chronic facial pain. Outcome predictors were also assessed.

METHODS

We randomized twenty consecutive patients with chronic facial pain (post-traumatic trigeminal neuropathic pain, n=14; persistent idiopathic facial pain, n=4; secondary trigeminal neuralgia, n=2) to receive two distinct 5-day rTMS interventions (10Hz, 2400 pulses and 20Hz, 3600 pulses) separated by six weeks. The target area was assessed by mapping of lower face representation. The primary endpoint was the change in weekly mean of pain intensity (numeric rating scale, NRS) between the baseline and therapy week (1^st week), and follow-up weeks (2^nd and 3^rd weeks) for each rTMS intervention. Response was defined using a combination scale including the patient's global impression of change and continuance with maintenance treatment.

RESULTS

Overall, pain intensity NRS decreased from 7.4 at baseline to 5.9 ten weeks later, after the second rTMS intervention (p=0.009). The repetition of the treatment had a significant effect (F=4.983, p=0.043) indicating that the NRS scores are lower during the second four weeks period. Eight (40%) patients were responders, 4 (20%) exhibited a modest effect, 4 (20%) displayed no effect, and 4 (20%) experienced worsening of pain. High disability and high pain intensity (>7) predicted a better outcome (p=0.043 and p=0.045). Female gender, shorter duration of pain and low Beck Anxiety Inventory scores showed a trend towards a better outcome (p=0.052, 0.060 and 0.055, respectively).

CONCLUSIONS

High-frequency rTMS targeted to face M1 alleviates treatment resistant chronic facial pain. Repeated treatment improves the analgesic effect. A protocol with higher frequency (above 10Hz), longer session duration (more than 20 minutes) and higher number of pulses (above 2400 pulses/session) did not improve the outcome. The results support early consideration of rTMS.

Insight Into the Effects of Clinical Repetitive Transcranial Magnetic Stimulation on the Brain From Positron Emission Tomography and Magnetic Resonance Imaging Studies: A Narrative Review

Repetitive transcranial magnetic stimulation (rTMS) has been proposed as a therapeutic tool to alleviate symptoms for neurological and psychiatric diseases such as chronic pain, stroke, Parkinson’s disease, major depressive disorder, and others. Although the therapeutic potential of rTMS has been widely explored, the neurological basis of its effects is still not fully understood. Fortunately, the continuous development of imaging techniques has advanced our understanding of rTMS neurobiological underpinnings on the healthy and diseased brain. The objective of the current work is to summarize relevant findings from positron emission tomography (PET) and magnetic resonance imaging (MRI) techniques evaluating rTMS effects. We included studies that investigated the modulation of neurotransmission (evaluated with PET and magnetic resonance spectroscopy), brain activity (evaluated with PET), resting-state connectivity (evaluated with resting-state functional MRI), and microstructure (diffusion tensor imaging). Overall, results from imaging studies suggest that the effects of rTMS are complex and involve multiple neurotransmission systems, regions, and networks. The effects of stimulation seem to not only be dependent in the frequency used, but also in the participants characteristics such as disease progression. In patient populations, pre-stimulation evaluation was reported to predict responsiveness to stimulation, while post-stimulation neuroimaging measurements showed to be correlated with symptomatic improvement. These studies demonstrate the complexity of rTMS effects and highlight the relevance of imaging techniques.

Evidence Mapping Based on Systematic Reviews of Repetitive Transcranial Magnetic Stimulation on the Motor Cortex for Neuropathic Pain

BACKGROUND AND OBJECTIVE

There is vast published literature proposing repetitive transcranial magnetic stimulation (rTMS) technology on the motor cortex (M1) for the treatment of neuropathic pain (NP). Systematic reviews (SRs) focus on a specific problem and do not provide a comprehensive overview of a research area. This study aimed to summarize and analyze the evidence of rTMS on the M1 for NP treatment through a new synthesis method called evidence mapping.

METHODS

Searches were conducted in PubMed, EMBASE, Epistemonikos, and The Cochrane Library to identify the studies that summarized the effectiveness of rTMS for NP. The study type was restricted to SRs with or without meta-analysis. All literature published before January 23, 2021, was included. Two reviewers independently screened the literature, assessed the methodological quality, and extracted the data. The methodological quality of the included SRs was assessed by using the A Measurement Tool to Assess Systematic Reviews (AMSTAR-2). Data were extracted following a defined population, intervention, comparison, and outcome (PICO) framework from primary studies that included SRs. The same PICO was categorized into PICOs according to interventions [frequency, number of sessions (short: 1-5 sessions, medium: 5-10 sessions, and long: >10 sessions)] and compared. The evidence map was presented in tables and a bubble plot.

RESULTS

A total of 38 SRs met the eligibility criteria. After duplicate primary studies were removed, these reviews included 70 primary studies that met the scope of evidence mapping. According to the AMSTAR-2 assessment, the quality of the included SRs was critically low. Of these studies, 34 SRs scored "critically low" in terms of methodological quality, 2 SR scored "low," 1 SR scored "moderate," and 1 SR scored "high."

CONCLUSION

Evidence mapping is a useful methodology to provide a comprehensive and reliable overview of studies on rTMS for NP. Evidence mapping also shows that further investigations are necessary to highlight the optimal stimulation protocols and standardize all parameters to fill the evidence gaps of rTMS. Given that the methodological quality of most included SRs was "critically low," further investigations are advised to improve the methodological quality and the reporting process of SRs.

Difference in Analgesic Effects of Repetitive Transcranial Magnetic Stimulation According to the Site of Pain

High-frequency repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex for neuropathic pain has been shown to be effective, according to systematic reviews and therapeutic guidelines. However, our large, rigorous, investigator-initiated, registration-directed clinical trial failed to show a positive primary outcome, and its subgroup analysis suggested that the analgesic effect varied according to the site of pain. The aim of this study was to investigate the differences in analgesic effects of rTMS for neuropathic pain between different pain sites by reviewing our previous clinical trials. We included three clinical trials in this mini meta-analysis: a multicenter randomized controlled trial at seven hospitals (N = 64), an investigator-initiated registration-directed clinical trial at three hospitals (N = 142), and an exploratory clinical trial examining different stimulation parameters (N = 22). The primary efficacy endpoint (change in pain scale) was extracted for each patient group with pain in the face, upper limb, or lower limb, and a meta-analysis of the efficacy of active rTMS against sham stimulation was performed. Standardized mean difference (SMD) with 95% confidence interval (CI) was calculated for pain change using a random-effects model. The analgesic effect of rTMS for upper limb pain was favorable (SMD = -0.45, 95% CI: -0.77 to -0.13). In contrast, rTMS did not produce significant pain relief on lower limb pain (SMD = 0.04, 95% CI: -0.33 to 0.41) or face (SMD = -0.24, 95% CI: -1.59 to 1.12). In conclusion, these findings suggest that rTMS provides analgesic effects in patients with neuropathic pain in the upper limb, but not in the lower limb or face, under the conditions of previous clinical trials. Owing to the main limitation of small number of studies included, many aspects should be clarified by further research and high-quality studies in these patients.

Exploratory study of optimal parameters of repetitive transcranial magnetic stimulation for neuropathic pain in the lower extremities

Introduction

Pain relief from repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex (M1) is particularly poor in patients with leg pain. The optimal parameters for relieving leg pain remain poorly understood. The purpose of this study was to explore the optimal stimulation parameters of M1-rTMS for patients with leg pain.

Methods

Eleven patients with neuropathic pain in the leg randomly underwent 6 conditions of M1-rTMS with different stimulation intensities, sites, and coil directions, including sham stimulation. The 5 active conditions were as follows: 90% or 110% of the resting motor threshold (RMT) on the M1 hand with an anteroposterior coil direction, 90% or 110% RMT on the M1 foot in the anteroposterior direction, and 90% RMT on the M1 foot in the mediolateral direction. Each condition was administered for 3 days. Pain intensity was evaluated using the Visual Analogue Scale and Short-Form McGill Pain Questionnaire 2 at baseline and up to 7 days after each intervention.

Results

Visual Analogue Scale scores were significantly reduced after the following active rTMS conditions: 90% RMT on the M1 hand, 90% RMT on the M1 foot with any coil direction, and 110% RMT on the M1 foot. The Short-Form McGill Pain Questionnaire 2 results were similar to those obtained using the Visual Analogue Scale. The analgesic effect of rTMS with stimulus intensity above the RMT was not superior to that below the RMT.

Conclusion

We suggest that the optimal stimulation parameters of rTMS for patients with neuropathic pain in the leg may target the M1 foot or M1 hand with an intensity below the RMT.

Repetitive Transcranial Magnetic Stimulation for Treating Chronic Neuropathic Pain: a Systematic Review

Given pharmacological interventions' limited efficacy and abundance of its adverse effects, the repetitive transcranial magnetic stimulation (rTMS) is considered a viable non-invasive option for managing chronic neuropathic pain of different origins with promising outcomes. PURPOSE OF REVIEW: The provision of a systematic review of current literature on rTMS for managing chronic neuropathic pain of different origins, and assess its efficacy and outcomes, highlighting the need for standard protocols for utilizing rTMS. RECENT FINDINGS: Variable stimulation modalities were trialed targeting the M1, DLPFC, and somatosensory cortices S1 and S2. The M1 yielded the best results in 11 of the studies. Frequency of stimulation was variable; however, optimal outcome was with higher frequencies ranging 10-20 Hz rather than low-frequency 1 Hz. Repetitive TMS can produce significant relief from chronic neuropathic pain. The lack of standard methods for rTMS, stimulatory parameters, and target stimulation site precludes concluding the optimal modality for stimulation. The practical algorithm by Lefaucheur and Nguyen (Neurophysiol Clin. 49(4):301-7, 2019) can guide setting standardized algorithms for rTMS. Defining optimal stimulation sites, frequencies, and pulses to maximize patient's pain relief and minimize required rTMS sessions requires further research.

Analgesic Effect of Noninvasive Brain Stimulation for Neuropathic Pain Patients: A Systematic Review

Introduction

The objective of this review is to systematically summarize the consensus on best practices for different NP conditions of the two most commonly utilized noninvasive brain stimulation (NIBS) technologies, repetitive transcranial magnetic stimulation (rTMS), and transcranial direct current stimulation (tDCS).

Methods

PubMed was searched according to the predetermined keywords and criteria. Only English language studies and studies published up to January 31, 2020 were taken into consideration. Meta-analyses, reviews, and systematic reviews were excluded first, and those related to animal studies or involving healthy volunteers were also excluded. Finally, 29 studies covering 826 NP patients were reviewed.

Results

The results from the 24 enrolled studies and 736 NP patients indicate that rTMS successfully relieved the pain symptoms of 715 (97.1%) NP patients. Also, five studies involving 95 NP patients (81.4%) also showed that tDCS successfully relieved NP. In the included studied, the M1 region plays a key role in the analgesic treatment of NIBS. The motor evoked potentials (MEPs), the 10–20 electroencephalography system (EEG 10/20 system), and neuro-navigation methods are used in clinical practice to locate therapeutic targets. Based on the results of the review, the stimulation parameters of rTMS that best induce an analgesic effect are a stimulation frequency of 10–20 Hz, a stimulation intensity of 80–120% of RMT, 1000–2000 pulses, and 5–10 sessions, and the most effective parameters of tDCS are a current intensity of 2 mA, a session duration of 20–30 min, and 5–10 sessions.

Conclusions

Our systematically reviewed the evidence for positive and negative responses to rTMS and tDCS for NP patient care and underscores the analgesic efficacy of NIBS in patients with NP. The treatment of NP should allow the design of optimal treatments for individual patients.

A randomized controlled trial of 5 daily sessions and continuous trial of 4 weekly sessions of repetitive transcranial magnetic stimulation for neuropathic pain

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Five daily sessions of repetitive transcranial magnetic stimulation with stimulus conditions were ineffective in neuropathic pain relief. Long-term administration should be investigated for clinical use of repetitive transcranial magnetic stimulation in neuropathic pain.

We conducted a multicenter, randomized, patient- and assessor-blinded, sham-controlled trial to investigate the efficacy of repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex (M1) in patients with neuropathic pain (NP). Patients were randomly assigned to receive 5 daily sessions of active or sham rTMS of M1 corresponding to the part of the body experiencing the worst pain (500 pulses per session at 5 Hz). Responders were invited to enroll in an open-label continuous trial involving 4 weekly sessions of active rTMS. The primary outcome was a mean decrease in a visual analogue scale of pain intensity (scaled 0-100 mm) measured daily during the daily sessions in an intention-to-treat population. Secondary outcomes were other pain scores, quality-of-life measures, and depression score. One hundred forty-four patients were assigned to the active or sham stimulation groups. The primary outcome, mean visual analogue scale decreases, was not significantly different (P = 0.58) between the active stimulation group (mean, 8.0) and the sham group (9.2) during the daily sessions. The secondary outcomes were not significantly different between 2 groups. The patients enrolled in the continuous weekly rTMS achieved more pain relief in the active stimulation group compared with the sham (P < 0.01). No serious adverse events were observed. Five daily sessions of rTMS with stimulus conditions used in this trial were ineffective in short-term pain relief in the whole study population with various NP. Long-term administration to the responders should be investigated for the clinical use of rTMS on NP in the future trials.

NIRS measures in pain and analgesia: Fundamentals, features, and function

Current pain assessment techniques based only on clinical evaluation and self-reports are not objective and may lead to inadequate treatment. Having a functional biomarker will add to the clinical fidelity, diagnosis, and perhaps improve treatment efficacy in patients. While many approaches have been deployed in pain biomarker discovery, functional near-infrared spectroscopy (fNIRS) is a technology that allows for non-invasive measurement of cortical hemodynamics. The utility of fNIRS is especially attractive given its ability to detect specific changes in the somatosensory and high-order cortices as well as its ability to measure (1) brain function similar to functional magnetic resonance imaging, (2) graded responses to noxious and innocuous stimuli, (3) analgesia, and (4) nociception under anesthesia. In this review, we evaluate the utility of fNIRS in nociception/pain with particular focus on its sensitivity and specificity, methodological advantages and limitations, and the current and potential applications in various pain conditions. Everything considered, fNIRS technology could enhance our ability to evaluate evoked and persistent pain across different age groups and clinical populations.

Repetitive transcranial magnetic stimulation of the primary motor cortex in management of chronic neuropathic pain: a systematic review

OBJECTIVES

Repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex (M1) with frequencies 5-20 Hz is an expanding non-invasive treatment for chronic neuropathic pain (NP). Outcome data, however, show considerable inhomogeneity with concern to the levels of effect due to the great diversity of treated conditions. The aim of this review was to survey the literature regarding the efficacy and safety of M1 rTMS, and the accuracy to predict a positive response to epidural motor cortex stimulation (MCS) which is supposed to give a more longstanding pain relief.

METHODS

A systematic literature search was conducted up to June 2019 in accordance with the PRISMA guidelines. We used the PICO Model to define two specific clinical questions: (1) Does rTMS of M1 relieve NP better than sham treatment? (2) Can the response to rTMS be used to predict the effect of epidural MCS? After article selection, data extraction, and study quality assessment, the certainty of evidence of treatment effect was defined using the GRADE system.

RESULTS

Data on 5-20 Hz (high-frequency) rTMS vs. sham was extracted from 24 blinded randomised controlled trials which were of varying quality, investigated highly heterogeneous pain conditions, and used excessively variable stimulation parameters. The difference in pain relief between active and sham stimulation was statistically significant in 9 of 11 studies using single-session rTMS, and in 9 of 13 studies using multiple sessions. Baseline data could be extracted from 6 single and 12 multiple session trials with a weighted mean pain reduction induced by active rTMS, compared to baseline, of -19% for single sessions, -32% for multiple sessions with follow-up <30 days, and -24% for multiple sessions with follow-up ≥30 days after the last stimulation session. For single sessions the weighted mean difference in pain reduction between active rTMS and sham was 15 percentage points, for multiple sessions the difference was 22 percentage points for follow-ups <30 days, and 15 percentage points for follow-ups ≥30 days. Four studies reported data that could be used to evaluate the accuracy of rTMS to predict response to MCS, showing a specificity of 60-100%, and a positive predictive value of 75-100%. No serious adverse events were reported.

CONCLUSIONS

rTMS targeting M1 can result in significant reduction of chronic NP which, however, is transient and shows a great heterogeneity between studies; very low certainty of evidence for single sessions and low for multiple sessions. Multiple sessions of rTMS can maintain a more longstanding effect. rTMS seems to be a fairly good predictor of a positive response to epidural MCS and may be used to select patients for implantation of permanent epidural electrodes. More studies are needed to manifest the use of rTMS for this purpose. Pain relief outcomes in a longer perspective, and outcome variables other than pain reduction need to be addressed more consistently in future studies to consolidate the applicability of rTMS in routine clinical practice.

Prolonged Continuous Theta Burst Stimulation of the Motor Cortex Modulates Cortical Excitability But not Pain Perception

Over the past decade, theta-burst stimulation (TBS) has become a focus of interest in neurostimulatory research. Compared to conventional repetitive transcranial magnetic stimulation (rTMS), TBS produces more robust changes in cortical excitability (CE). There is also some evidence of an analgesic effect of the method. Previously published studies have suggested that different TBS parameters elicit opposite effects of TBS on CE. While intermittent TBS (iTBS) facilitates CE, continuous TBS (cTBS) attenuates it. However, prolonged TBS (pTBS) with twice the number of stimuli produces the opposite effect. In a double-blind, placebo-controlled, cross-over study with healthy subjects (n = 24), we investigated the effects of various pTBS (cTBS, iTBS, and placebo TBS) over the right motor cortex on CE and pain perception. Changes in resting motor thresholds (RMTs) and absolute motor-evoked potential (MEP) amplitudes were assessed before and at two time-points (0–5 min; 40–45 min) after pTBS. Tactile and thermal pain thresholds were measured before and 5 min after application. Compared to the placebo, prolonged cTBS (pcTBS) transiently increased MEP amplitudes, while no significant changes were found after prolonged iTBS. However, the facilitation of CE after pcTBS did not induce a parallel analgesic effect. We confirmed that pcTBS with twice the duration converts the conventional inhibitory effect into a facilitatory one. Despite the short-term boost of CE following pcTBS, a corresponding analgesic effect was not demonstrated. Therefore, the results indicate a more complex regulation of pain, which cannot be explained entirely by the modulation of excitability.

Long-term treatment of chronic orofacial, pudendal, and central neuropathic limb pain with repetitive transcranial magnetic stimulation of the motor cortex

OBJECTIVE

To assess the long-term analgesic effects of high-frequency repetitive transcranial magnetic stimulation (rTMS) of the motor cortex in patients with chronic pain syndrome.

METHODS

The study included 57 patients (orofacial pain, n = 26, pudendal neuralgia, n = 18, and neuropathic limb pain, n = 13) with an "induction phase" of 12 daily rTMS sessions for 3 weeks, followed by a "maintenance phase" of bi-monthly sessions for the next five months.

RESULTS

All pain measures significantly decreased from baseline to the end of the induction phase. Analgesic response, defined as pain intensity decrease ≥ 30% compared to baseline, was observed in 39 patients (68%), who could be differentiated from non-responders from the 7th rTMS session. At the end of the maintenance phase (D180), 27 patients (47%) were still responders. Anxio-depressive symptoms and quality of life also improved. The analgesic response at the end of the induction phase was associated with lower pain score at baseline, and the response at the end of the maintenance phase was associated with lower anxio-depressive score at baseline.

CONCLUSION

The analgesic efficacy of motor cortex rTMS can be maintained in the long term in various chronic pain conditions. Patients with high pain level and severe anxio-depressive symptoms may have a less favorable profile to respond to the procedure.

SIGNIFICANCE

The overall impact of rTMS treatment on daily life requires a multidimensional evaluation that goes beyond the analgesic effect that can be achieved.

Effect of Repetitive Transcranial Magnetic Stimulation on Pain Management: A Systematic Narrative Review

Recently, clinicians have been using repetitive transcranial magnetic stimulation (rTMS) for treating various pain conditions. This systematic narrative review aimed to examine the use and efficacy of rTMS for controlling various pain conditions. A PubMed search was conducted for articles that were published until June 7, 2019 and used rTMS for pain alleviation. The key search phrase for identifying potentially relevant articles was (repetitive transcranial magnetic stimulation AND pain). The following inclusion criteria were applied for article selection: (1) patients with pain, (2) rTMS was applied for pain management, and (3) follow-up evaluations were performed after rTMS stimulation to assess the reduction in pain. Review articles were excluded. Overall, 1,030 potentially relevant articles were identified. After reading the titles and abstracts and assessing eligibility based on the full-text articles, 106 publications were finally included in our analysis. Overall, our findings suggested that rTMS is beneficial for treating neuropathic pain of various origins, such as central pain, pain from peripheral nerve disorders, fibromyalgia, and migraine. Although data on the use of rTMS for orofacial pain, including trigeminal neuralgia, phantom pain, low back pain, myofascial pain syndrome, pelvic pain, and complex regional pain syndrome, were promising, there was insufficient evidence to determine the efficacy of rTMS for treating these conditions. Therefore, further studies are needed to validate the effects of rTMS on pain relief in these conditions. Overall, this review will help guide clinicians in making informed decisions regarding whether rTMS is an appropriate option for managing various pain conditions.

Evidence-based guidelines on the therapeutic use of repetitive transcranial magnetic stimulation (rTMS): An update (2014-2018)

A group of European experts reappraised the guidelines on the therapeutic efficacy of repetitive transcranial magnetic stimulation (rTMS) previously published in 2014 [Lefaucheur et al., Clin Neurophysiol 2014;125:2150-206]. These updated recommendations take into account all rTMS publications, including data prior to 2014, as well as currently reviewed literature until the end of 2018. Level A evidence (definite efficacy) was reached for: high-frequency (HF) rTMS of the primary motor cortex (M1) contralateral to the painful side for neuropathic pain; HF-rTMS of the left dorsolateral prefrontal cortex (DLPFC) using a figure-of-8 or a H1-coil for depression; low-frequency (LF) rTMS of contralesional M1 for hand motor recovery in the post-acute stage of stroke. Level B evidence (probable efficacy) was reached for: HF-rTMS of the left M1 or DLPFC for improving quality of life or pain, respectively, in fibromyalgia; HF-rTMS of bilateral M1 regions or the left DLPFC for improving motor impairment or depression, respectively, in Parkinson's disease; HF-rTMS of ipsilesional M1 for promoting motor recovery at the post-acute stage of stroke; intermittent theta burst stimulation targeted to the leg motor cortex for lower limb spasticity in multiple sclerosis; HF-rTMS of the right DLPFC in posttraumatic stress disorder; LF-rTMS of the right inferior frontal gyrus in chronic post-stroke non-fluent aphasia; LF-rTMS of the right DLPFC in depression; and bihemispheric stimulation of the DLPFC combining right-sided LF-rTMS (or continuous theta burst stimulation) and left-sided HF-rTMS (or intermittent theta burst stimulation) in depression. Level A/B evidence is not reached concerning efficacy of rTMS in any other condition. The current recommendations are based on the differences reached in therapeutic efficacy of real vs. sham rTMS protocols, replicated in a sufficient number of independent studies. This does not mean that the benefit produced by rTMS inevitably reaches a level of clinical relevance.

Noninvasive Transcranial Magnetic Stimulation (TMS) in Chronic Refractory Pain: A Systematic Review

Efficacy and tolerance of pharmacological medications in chronic pain are limited. Therefore, repetitive transcranial magnetic stimulation (rTMS) is regarded as a secure therapeutic option for pain relief, and it was proven to produce an analgesic effect. A wide variety of stimulation parameters can influence its long-lasting antalgic effect. Defining the best stimulation protocol can afford greater uniformity and consistency for considering rTMS as a promising effective tool. We aimed to systematically review and evaluate the current literature on transcranial magnetic stimulation for patients suffering from chronic pain, assess its efficacy, and estimate the best stimulation protocol. The Screened and tested electronic databases comprised PubMed, Ovid Medline, Cochrane database library, and Google scholar from the year 2000 till 2018. The keywords utilizing search terms “Transcranial magnetic stimulation”, “chronic pain”, “neuropathic pain” were used to study all possible randomized clinical trials about the impact of transcranial magnetic stimulation on long-lasting pain. All articles were judged for the possibility of prejudice using the Cochrane risk of bias tool for data extraction. Search engines produced seventy applicable results. Twelve randomized controlled clinical trials were included involving 350 patients with focal and generalized chronic pain. An existing proof showed a null response of low-frequency rTMS stimulation, rTMS delivered to the dorsolateral prefrontal cortex in chronic pain patients. However, a witnessed pain-killing response was documented when applying active high- frequency TMS on the motor cortex M1 area compared to sham. Pain relief was detected for a short time following the application of active high-frequency motor cortex stimulation in nine clinical trials, and the long-lasting analgesic effect was proved. No side effects were mentioned for the technique. Repetitive TMS can produce clinically meaningful relief from chronic pain, despite positive results, heterogeneity among all studies preclude firm conclusions regarding the optimal target stimulation site and parameters. Further studies are required to minimize bias, enhance performance, and define the best brain stimulation conditions and qualifications to maximize its potency. 

Cortical modulation of nociception by galvanic vestibular stimulation: A potential clinical tool?

OBJECTIVE

Vestibular afferents converge with nociceptive ones within the posterior insula, and can therefore modulate nociception. Consistent with this hypothesis, caloric vestibular stimulation (CVS) has been shown to reduce experimental and clinical pain. Since CVS can induce undesirable effects in a proportion of patients, here we explored an alternative means to activate non-invasively the vestibular pathways using innocuous bi-mastoid galvanic stimulation (GVS), and assessed its effects on experimental pain.

METHODS

Sixteen healthy volunteers participated in this study. Experimental pain was induced by noxious laser-heat stimuli to the left hand while recording pain ratings and related brain potentials (LEPs). We evaluated changes of these indices during left- or right-anodal GVS (cathode on contralateral mastoid), and contrasted them with those during sham GVS, optokinetic vestibular stimulation (OKS) using virtual reality, and attentional distraction to ascertain the vestibular-specific analgesic effects of GVS.

RESULTS

GVS elicited brief sensations of head/trunk deviation, inoffensive to all participants. Both active GVS conditions showed analgesic effects, greater for the right anodal stimulation. OKS was helpful to attain significant LEP reductions during the left-anodal stimulation. Neither sham-GVS nor the distraction task were able to modulate significantly pain ratings or LEPs.

CONCLUSIONS

GVS appeared as a well-tolerated and powerful procedure for the relief of experimental pain, probably through physiological interaction within insular nociceptive networks. Either isolated or in combination with other types of vestibular activation (e.g., optokinetic stimuli), GVS deserves being tested in clinical settings.

Neurostimulation methods in the treatment of chronic pain

The goal of this narrative review was to give an up-to-date overview of the peripheral and central neurostimulation methods that can be used to treat chronic pain. Special focus has been given to three pain conditions: neuropathic pain, nociplastic pain and primary headaches. Both non-invasive and invasive techniques are briefly presented together with their pain relief potentials. For non-invasive stimulation techniques, data concerning transcutaneous electrical nerve stimulation (TENS), transcranial direct current stimulation (tDCS), repetitive transcranial magnetic stimulation (rTMS), remote electrical neuromodulation (REN) and vagus nerve stimulation (VNS) are provided. Concerning invasive stimulation techniques, occipital nerve stimulation (ONS), vagus nerve stimulation (VNS), epidural motor cortex stimulation (EMCS), spinal cord stimulation (SCS) and deep brain stimulation (DBS) are presented. The action mode of all these techniques is only partly understood but can be very different from one technique to the other. Patients' selection is still a challenge. Recent consensus-based guidelines for clinical practice are presented when available. The development of closed-loop devices could be of interest in the future, although the clinical benefit over open loop is not proven yet.

At-Home Cortical Stimulation for Neuropathic Pain: a Feasibility Study with Initial Clinical Results

The clinical use of noninvasive cortical stimulation procedures is hampered by the limited duration of the analgesic effects and the need to perform stimulation in hospital settings. Here, we tested the feasibility and pilot efficacy of an internet-based system for at-home, long-duration, medically controlled transcranial motor cortex stimulation (H-tDCS), via a double-blinded, sham-controlled trial in patients with neuropathic pain refractory to standard-of-care drug therapy. Each patient was first trained at hospital, received a stimulation kit, allotted a password-protected Web space, and completed daily tDCS sessions during 5 weeks, via a Bluetooth connection between stimulator and a minilaptop. Each session was validated and internet-controlled by hospital personnel. Daily pain ratings were obtained during 11 consecutive weeks, and afterwards via iterative visits/phone contacts. Twenty full procedures were completed in 12 consecutive patients (500 daily tDCS sessions, including 20% sham). No serious adverse effects were recorded. Superficial burning at electrode position occurred in 2 patients, and nausea/headache in two others, all of whom wished to pursue stimulation. Six out of the 12 patients achieved satisfactory relief on a scale combining pain scores, drug intake, and quality of life. Daily pain reports correlated with such combined assessment, and differentiated responders from nonresponders without overlap. Clinical improvement in responders could last up to 6 months. Five patients asked to repeat the whole procedure when pain resumed again, with comparable results. At-home, long-duration tDCS proved safe and technically feasible, and provided long-lasting relief in 50% of a small sample of patients with drug-resistant neuropathic pain.

A practical algorithm for using rTMS to treat patients with chronic pain

High-frequency repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex has a good level of evidence of efficacy as a method for providing analgesic effects in patients with chronic pain. However, there is still no consensus regarding the parameters of stimulation to use and the detailed protocol to apply for therapeutic practice. In this article, we review the main technical points to address, and we propose a practical algorithm of how to use rTMS for chronic pain treatment in daily clinical practice.

Repetitive Transcranial Magnetic Stimulation Therapy (rTMS) for Endometriosis Patients with Refractory Pelvic Chronic Pain: A Pilot Study

Endometriosis concerns more than 10% of women of reproductive age, frequently leading to chronic pelvic pain. Repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex (M1) induces an analgesic effect. This effect on chronic pelvic pain is yet to be evaluated. The objective of this study was to assess the feasibility and effect of rTMS to reduce pain and improve quality of life (QoL) in patients with chronic pelvic pain due to endometriosis. This pilot, open-labelled prospective trial examined treatment by neuronavigated rTMS over M1, one session per day for 5 consecutive days. Each session consisted of 1.500 pulses at 10 Hz. We assessed tolerance, pain change and QoL until 4 weeks post treatment with a primary endpoint at day 8. Twelve women were included. No patients experienced serious adverse effects or a significant increase in pain. Nine women reported improvement on the Patient Global Impression of Change with a reduction in both pain intensity and pain interference (5.1 ± 1.4 vs. 4.1 ± 1.6, p = 0.01 and 6.2 ± 2.1 vs. 4.2 ± 1.5, p = 0.004, respectively). rTMS appears well tolerated and might be of interest for patients suffering from chronic pelvic pain for whom other treatments have failed. A randomized controlled trial is mandatory before proposing such treatment.

Thermovision: a new diagnostic method for orofacial pain?

BACKGROUND

Infrared thermography can be used to obtain more complete information about a patient's condition. The method can be used in various medical applications for monitoring acute and chronic orofacial pain syndrome. With this diagnostic method, thermal differences in the examined region are usually compared to the same reference region on the opposite side of the body.

METHODS

Infrared quantitative thermography is a non-invasive method for contactless monitoring of dynamic thermal fields on a surface, or in this case, the human body. This method is based on detection of infrared radiation, which is naturally emitted from the surface of the body. In a pilot project with a patient having orofacial pain, changes before and after repetitive transcranial magnetic brain stimulation treatment were assessed.

RESULTS

First-day measurements found significantly higher maximum, minimum, and average temperatures, before and after therapy, in the area where the patient subjectively reported pain. The fifth and final measurements, before and after therapy, found only a slight elevation of the maximum temperature of the assessed regions, relative to the same regions on the opposite side of the face.

CONCLUSION

During the measurements on the fifth day, a thermal difference greater than 0.4°C was only observed relative to the minimum temperatures associated with the regions of self-reported pain before and after therapy. For validation of the effects, this method will need to be tested using a randomized, double-blind study with a larger number of patients.

Non-invasive brain stimulation in chronic orofacial pain: a systematic review

Background

Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are non-invasive brain stimulation techniques that are being explored as therapeutic alternatives for the management of various chronic pain conditions.

Objective

The primary objective of this systematic review is to assess the efficacy of TMS and tDCS in reducing clinical pain intensity in chronic orofacial pain (OFP) disorders. The secondary objectives are to describe adverse effects, duration of relief, and TMS/tDCS methodologies used in chronic OFP disorders.

Methods

A search was performed in MEDLINE, Embase, Web of Science, Scopus, and Google Scholar. Inclusion criteria were 1) population: adults diagnosed with chronic OFP including neuropathic and non-neuropathic disorders; 2) intervention: active TMS or tDCS stimulation regardless of the used protocol; 3) comparison: sham TMS or tDCS stimulation; and 4) outcome: primary outcome was patient reported pain intensity. Secondary outcomes were duration of pain relief, adverse effects, and methodological parameters. Risk of bias and quality of study reporting were also assessed.

Results

A total of 556 individual citations were identified by the search strategy, with 14 articles meeting selection criteria (TMS=11; tDCS=3). Data were obtained for a total of 228 patients. Included OFP disorders were trigeminal neuralgia, trigeminal neuropathy, burning mouth syndrome, atypical facial pain, and temporomandibular disorders. Significant pain reductions were obtained in both techniques. More number of sessions yielded to more durable effects. Overall, high risk of bias and poor study quality were found.

Conclusion

TMS and tDCS appear to be safe and promising alternatives to reduce pain intensity in different chronic OFP disorders. Additional research effort is needed to reduce bias, improve quality, and characterize optimal brain stimulation parameters to promote their efficacy.