Reduction of intractable deafferentation pain by navigation-guided repetitive transcranial magnetic stimulation of the primary motor cortex

Predictors for quality of life improvement following rTMS treatment in neuropathic pain patients

OBJECTIVES

Recently, Repetitive Transcranial Magnetic Stimulation (rTMS) has gained attention for its potential in relieving neuropathic pain (NP). NP encompasses central and peripheral neuralgia, characterized by sensory abnormalities and spontaneous pain. Pharmacological treatments often provide partial relief with significant side effects, making rTMS an attractive alternative. This study aimed to assess the efficacy of rTMS in treating NP and its impact on quality of life over three months.

METHODS

A total of 51 patients with drug-resistant NP were included, undergoing 15 sessions of rTMS targeting motor cortex areas over three weeks. Clinical response was evaluated using various psychometric scales, including VAS for pain and PGIC. Quality of life was assessed using the SF-36 questionnaire.

RESULTS

Results showed significant clinical improvements in pain severity and quality of life following rTMS treatment. Predictive factors of quality of life improvement were identified, with mental health being crucial across all NP areas. Notably, patients with cerebral NP showed improvements linked to physical dimensions, emphasizing tailored treatment approaches.

CONCLUSIONS

This study underscores the efficacy of rTMS in managing NP, highlighting sustained improvements in pain severity and quality of life. The findings offer valuable insights for personalized treatment approaches and optimizing patient outcomes in NP management.

Assessing the effectiveness of high frequency repetitive transcranial magnetic stimulation for post-mastectomy pain in breast cancer patients: A randomized controlled trial

BACKGROUND

Post-mastectomy pain Syndrome (PMPS), characterized by chronic neuropathic pain stemming from intercostobrachial nerve lesions, presents a formidable clinical challenge. With the incidence of breast cancer surging, effective interventions for PMPS are urgently needed. To address this, we conducted this double-blind, placebo-controlled, randomized clinical trial to study the efficacy of repetitive Transcranial Magnetic Stimulation (rTMS) therapy over the motor cortex on pain, quality of life and thermal sensitivity in PMPS patients.

METHODS

We delivered 15 rTMS sessions over three weeks in a cohort of 34 PMPS patients. These patients were allocated randomly to either rTMS therapy or sham therapy groups. Pain assessments, utilizing the Visual Analogue Scale (VAS) and Short Form McGill Pain Questionnaire (SF-MPQ), alongside quality-of-life evaluations through the Functional Assessment of Cancer Therapy-Breast (FACT-B), were recorded before and after the 15 sessions. Additionally, we assessed thermal sensitivity using Quantitative Sensory Testing (QST).

RESULTS

Our findings demonstrate the superior efficacy of rTMS therapy (over sham therapy) in reducing VAS and SF-MPQ scores (p < 0.0001), improving physical (p = 0.037), emotional (p = 0.033), and functional well-being (p = 0.020) components of quality of life, as quantified by FACT-B. Our investigation also unveiled marked enhancements in thermal sensitivity within the rTMS therapy group, with statistically significant improvements in cold detection threshold (p = 0.0001), warm detection threshold (p = 0.0033), cold pain threshold (p = 0.0078), and hot pain tolerance threshold (p = 0.0078).

CONCLUSION

The study underscores the profound positive impact of rTMS therapy on pain, quality of life, and thermal sensitivity in patients having PMPS, opening new avenues for pain management strategies.

Brain activity changes after high/low frequency stimulation in a nonhuman primate model of central post-stroke pain

Central post-stroke pain (CPSP) is a chronic pain resulting from a lesion in somatosensory pathways. Neuromodulation techniques, such as repetitive transcranial magnetic stimulation (rTMS) that target the primary motor cortex (M1), have shown promise for the treatment of CPSP. High-frequency (Hf) rTMS exhibits analgesic effects compared to low-frequency (Lf) rTMS; however, its analgesic mechanism is unknown. We aimed to elucidate the mechanism of rTMS-induced analgesia by evaluating alterations of tactile functional magnetic resonance imaging (fMRI) due to Hf- and Lf-rTMS in a CPSP monkey model. Consistent with the patient findings, the monkeys showed an increase in pain threshold after Hf-rTMS, which indicated an analgesic effect. However, no change after Lf-rTMS was observed. Compared to Lf-rTMS, Hf-rTMS produced enhanced tactile-evoked fMRI signals not only in M1 but also in somatosensory processing regions, such as the primary somatosensory and midcingulate cortices. However, the secondary somatosensory cortex (S2) was less active after Hf-rTMS than after Lf-rTMS, suggesting that activation of this region was involved in CPSP. Previous studies showed pharmacological inhibition of S2 reduces CPSP-related behaviors, and the present results emphasize the involvement of an S2 inhibitory system in rTMS-induced analgesia. Verification using the monkey model is important to elucidate the inhibition system.

Repetitive transcranial magnetic stimulation focusing on patients with neuropathic pain in the upper limb: a randomized sham-controlled parallel trial

This study aimed to evaluate the efficacy and safety of navigation-guided repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex in patients with neuropathic pain in the upper limb. This randomized, blinded, sham-controlled, parallel trial included a rTMS protocol (10-Hz, 2000 pulses/session) consisting of five daily sessions, followed by one session per week for the next seven weeks. Pain intensity, as well as pain-related disability, quality of life, and psychological status, were assessed. For the primary outcome, pain intensity was measured daily using a numerical rating scale as a pain diary. Thirty patients were randomly assigned to the active rTMS or sham-stimulation groups. In the primary outcome, the decrease (least square [LS] mean ± standard error) in the weekly average of a pain diary at week 9 compared to the baseline was 0.84 ± 0.31 in the active rTMS group and 0.58 ± 0.29 in the sham group (LS mean difference, 0.26; 95% confidence interval, - 0.60 to 1.13). There was no significant effect on the interaction between the treatment group and time point. Pain-related disability score improved, but other assessments showed no differences. No serious adverse events were observed. This study did not show significant pain relief; however, active rTMS tended to provide better results than sham. rTMS has the potential to improve pain-related disability in addition to pain relief.Clinical Trial Registration number: jRCTs052190110 (20/02/2020).

High frequency neuronavigated repetitive transcranial magnetic stimulation in post-stroke shoulder pain: A double-blinded, randomized controlled study

OBJECTIVE

This study aimed to determine the effect of 5Hz neuronavigated repetitive transcranial magnetic stimulation (rTMS) to the affected primary motor cortex (M1) on pain, the effect of pain on activities of daily living, disability, mood, neurophysiological parameters and passive shoulder joint range of motion in patients with post-stroke shoulder pain.

DESIGN

Twenty two patients were randomized into an experimental group (rTMS, n=7) who received daily rTMS 5Hz 1000 pulses, five times/week for three weeks (15 sessions) to the affected M1 and a control group (n=11) who received sham stimulation. Outcome measures were Numeric Rating Scale (NRS), Brief Pain Inventory (BPI), Disabilities of the arm, shoulder, and hand questionnaire (Quick DASH), Hospital Depression Anxiety Scale (HADS), joint range of motion (ROM) measurements, neurophysiological parameters. Selected outcome measures were performed before treatment (T0), after the 5th session (T1) of rTMS treatment, after the 10th session (T2), after the 15th session (T3), and four weeks after the end of the treatment (T4). In the analysis of the outcomes, within-group comparisons were performed by using the Wilcoxon or Friedman test and between-group comparisons were performed by using the Mann-Whitney U test.

RESULTS

There was no statistically significant difference between and within groups in terms of change- and followup scores in the NRS measurements (p>0.05). BPI scale was found to be lower in rTMS group at T0 and T3 (p= 0.010). Quick-DASH scores at T4 were found to be significantly lower in rTMS group (p= 0.032). However, no difference was found within each group over time (p>0.05) and there was no statistical difference between the groups in terms of change scores (T3-T0 and T4-T0) (p>0.05) for BPI and Quick-DASH. In rTMS group, there was a statistically significant difference in shoulder external rotation at T3 compared to the baseline (T0) (p=0.039). However, the magnitude of external rotation change (T3-T0) with the treatment was comparable in the groups. No statistically significant change occurred in both treatment groups in other range of motion measurements.

CONCLUSION

High frequency neuronavigated rTMS to the affected M1 did not show any significant beneficial effect on pain, activities of daily living, disability, anxiety and depression, neurophysiological measurements and passive ROM over sham stimulation.

Transcranial magnetic stimulation therapy for central post-stroke pain: systematic review and meta-analysis

Introduction

Although rare, central post-stroke pain remains one of the most refractory forms of neuropathic pain. It has been reported that repetitive transcranial magnetic stimulation (rTMS) may be effective in these cases of pain.

Aim

The aim of this study was to investigate the efficacy of rTMS in patients with central post-stroke pain (CPSP).

Methods

We included randomized controlled trials or Controlled Trials published until October 3rd, 2022, which studied the effect of rTMS compared to placebo in CPSP. We included studies of adult patients (>18 years) with a clinical diagnosis of stroke, in which the intervention consisted of the application of rTMS to treat CSP.

Results

Nine studies were included in the qualitative analysis; 6 studies (4 RCT and 2 non-RCT), with 180 participants, were included in the quantitative analysis. A significant reduction in CPSP was found in favor of rTMS compared with sham, with a large effect size (SMD: -1.45; 95% CI: -1.87; -1.03; p < 0.001; I2: 58%).

Conclusion

The findings of the present systematic review with meta-analysis suggest that there is low quality evidence for the effectiveness of rTMS in reducing CPSP.

Systematic review registration

Identifier (CRD42022365655).

Transcranial magnetic stimulation in the treatment of phantom limb pain: a systematic review

BACKGROUND

 Phantom limb pain (PLP) occurs after amputations and can persist in a chronic and debilitating way. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive neuromodulation method capable of influencing brain function and modulating cortical excitability. Its effectiveness in treating chronic pain is promising.

OBJECTIVE

 To evaluate the evidence on the efficacy and safety of using rTMS in the treatment of PLP, observing the stimulation parameters used, side effects, and benefits of the therapy.

METHODS

 This is a systematic review of scientific articles published in national and international literature using electronic platforms.

RESULTS

 Two hundred and fifty two articles were identified. Two hundred and forty six publications were removed because they were duplicated or met the exclusion criteria. After selection, six studies were reviewed, those being two randomized clinical trials and four case reports. All evaluated studies indicated some degree of benefit of rTMS to relieve painful symptoms, even temporarily. Pain perception was lower at the end of treatment when compared to the period prior to the sessions and remained during patient follow-up. There was no standardization of the stimulation parameters used. There were no reports of serious adverse events. The effects of long-term therapy have not been evaluated.

CONCLUSION

 There are some benefits, even if temporary, in the use of rTMS to relieve painful symptoms in PLP. High-frequency stimulation at M1 demonstrated a significant analgesic effect. Given the potential that has been demonstrated, but limited by the paucity of high-quality studies, further controlled studies are needed to establish and standardize the clinical use of the method.

The Hypoalgesic Effect of Low-Load Exercise to Failure Is Not Augmented by Blood Flow Restriction

Purpose: To 1) examine whether blood flow restriction would provide an additional exercise-induced hypoalgesic response at an upper and lower limb when it is incorporated with low-load resistance exercise until failure, and 2) examine if increases in blood pressure and discomfort, with blood flow restricted exercise, would mediate the exercise-induced hypoalgesia over exercise without blood flow restriction. Methods: Forty healthy young participants completed two trials: four sets of unilateral knee extension exercise to failure at 30% of one-repetition maximum, with and without blood flow restriction. Pressure pain thresholds were assessed before (twice) and 5-min post exercise at an upper and lower limb. Blood pressure and discomfort ratings were recorded to examine mediating effects on exercise-induced hypoalgesia with blood flow restricted exercise. Results: Pressure pain threshold increased following both exercise conditions compared to a control, without any differences between exercise conditions at the upper (exercise conditions vs. control: ~0.37 kg/cm2) and lower (exercise conditions vs. control: ~0.60 kg/cm2) limb. The total number of repetitions was lower for exercise with blood flow restriction compared to exercise alone [median difference (95% credible interval) of -27.0 (-29.8, -24.4) repetitions]. There were no mediating effects of changes in blood pressure, nor changes in discomfort, for the changes in pressure pain threshold at either the upper or lower limb. Conclusion: The addition of blood flow restriction to low-load exercise induces a similar hypoalgesic response to that of non-blood flow restricted exercise, with a fewer number of repetitions.

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.

Network targets for therapeutic brain stimulation: towards personalized therapy for pain

Precision neuromodulation of central brain circuits is a promising emerging therapeutic modality for a variety of neuropsychiatric disorders. Reliably identifying in whom, where, and in what context to provide brain stimulation for optimal pain relief are fundamental challenges limiting the widespread implementation of central neuromodulation treatments for chronic pain. Current approaches to brain stimulation target empirically derived regions of interest to the disorder or targets with strong connections to these regions. However, complex, multidimensional experiences like chronic pain are more closely linked to patterns of coordinated activity across distributed large-scale functional networks. Recent advances in precision network neuroscience indicate that these networks are highly variable in their neuroanatomical organization across individuals. Here we review accumulating evidence that variable central representations of pain will likely pose a major barrier to implementation of population-derived analgesic brain stimulation targets. We propose network-level estimates as a more valid, robust, and reliable way to stratify personalized candidate regions. Finally, we review key background, methods, and implications for developing network topology-informed brain stimulation targets for chronic pain.

Low-Intensity Blood Flow Restriction Exercises Modulate Pain Sensitivity in Healthy Adults: A Systematic Review

Low-intensity exercise with blood flow restriction (LIE-BFR) has been proposed as an effective intervention to induce hypoalgesia in both healthy individuals and patients with knee pain. Nevertheless, there is no systematic review reporting the effect of this method on pain threshold. We aimed to evaluate the following: (i) the effect of LIE-BFR on pain threshold compared to other interventions in patients or healthy individuals; and (ii) how different types of applications may influence hypoalgesic response. We included randomized controlled trials assessing the effectiveness of LIE-BFR alone or as an additive intervention compared with controls or other interventions. Pain threshold was the outcome measure. Methodological quality was assessed using the PEDro score. Six studies with 189 healthy adults were included. Five studies were rated with 'moderate' and 'high' methodological quality. Due to substantial clinical heterogeneity, quantitative synthesis could not be performed. All studies used pressure pain thresholds (PPTs) to assess pain sensitivity. LIE-BFR resulted in significant increases in PPTs compared to conventional exercise at local and remote sites 5 min post-intervention. Higher-pressure BFR results in greater exercise-induced hypoalgesia compared to lower pressure, while exercise to failure produces a similar reduction in pain sensitivity with or without BFR. Based on our findings, LIE-BFR can be an effective intervention to increase pain threshold; however, the effect depends on the exercise methodology. Further research is necessary to investigate the effectiveness of this method in reducing pain sensitivity in patients with pain symptomatology.

Applications for oral research in microgravity - lessons learned from burning mouth syndrome and ageing studies

The negative consequences of microgravity for the human body are central aspects of space travel that raise health problems. Altered functions of the same systems and treatment options are common points of spaceflight physiology, age-related diseases, and oral medicine. This work emphasizes the convergence of knowledge between pathophysiological changes brought on by aging, physiological reactions to microgravity exposure, and non-pharmacological and non-invasive treatment methods that can be used in spaceflight. Sarcopenia, peripheral nerves alterations, neuromotor plaque in the masticatory muscles, lingual, labial, and buccal weakness, nociplastic pain in oral mucosal diseases, and microgravity, as well as soft tissue changes and pathologies related to chewing and swallowing, corticomotor neuroplasticity of tongue, and swallowing biomechanics, are of particular interest to us. Neurologic disease and other pathologies such as recovery from post-stroke dysphagia, nociplastic pain in glossodynia, sleep bruxism, and obstructive sleep apnea have been studied and, in some cases, successfully treated with non-invasive direct and transcranial magnetic stimulation (TMS) methods in recent decades. An interdisciplinary team from medical specialties, engineering, and biophysics propose an exploratory study based on the parallelism of ageing and space physiology, along with experiment scenarios considering TMS and non-invasive direct methods.

The mechanism and effect of repetitive transcranial magnetic stimulation for post-stroke pain

Post-stroke pain (PSP) is a common complication after stroke and affects patients' quality of life. Currently, drug therapy and non-invasive brain stimulation are common treatments for PSP. Given the poor efficacy of drug therapy and various side effects, non-invasive brain stimulation, such as repetitive transcranial magnetic stimulation (rTMS), has been accepted by many patients and attracted the attention of many researchers because of its non-invasive and painless nature. This article reviews the therapeutic effect of rTMS on PSP and discusses the possible mechanisms. In general, rTMS has a good therapeutic effect on PSP. Possible mechanisms of its analgesia include altering cortical excitability and synaptic plasticity, modulating the release of related neurotransmitters, and affecting the structural and functional connectivity of brain regions involved in pain processing and modulation. At present, studies on the mechanism of rTMS in the treatment of PSP are lacking, so we hope this review can provide a theoretical basis for future mechanism studies.

Exercised-Induced Hypoalgesia following An Elbow Flexion Low-Load Resistance Exercise with Blood Flow Restriction: A Sham-Controlled Randomized Trial in Healthy Adults

We aimed to evaluate the hypoalgesic effect of an elbow flexion low-load resistance exercise with blood flow restriction (LLRE-BFR) when compared to high-load resistance exercise (HLRE) with sham-BFR in healthy individuals. Forty healthy young adults (17 women), with a mean age ± SD: 26.6 ± 6.8 years, and mean body mass index ± SD: 23.6 ± 2.7 were randomly assigned to either an LLRE-BFR (30% 1 repetition maximum, RM) or an HLRE with sham-BFR group (70% of 1 RM). Blood pressure and pressure pain thresholds (PPTs) were measured pre- and post-exercise intervention. The rating of perceived exertion (RPE) was recorded after each set. There were non-significant between-group changes in PPT at the dominant biceps (-0.61, 95%CI: -1.92 to 0.68) with statistically significant reductions between pre- and post-exercise in LLRE-BFR (effect size, d = 0.88) and HLRE-BFR (effect size, d = 0.52). No within- or between-group differences were recorded in PPT at non-exercising sites of measurement. No mediating effects of changes in blood pressure or RPE on the changes in pressure pain threshold were observed. LLRE-BFR produced a similar hypoalgesic effect locally compared to HLRE and can be used as an alternative intervention to decrease pain sensitivity when HLRE is contraindicated or should be avoided.

Network Effects of Brain Lesions Causing Central Poststroke Pain

OBJECTIVE

This study was undertaken to test whether lesions causing central poststroke pain (CPSP) are associated with a specific connectivity profile, whether these connections are associated with metabolic changes, and whether this network aligns with neuromodulation targets for pain.

METHODS

Two independent lesion datasets were utilized: (1) subcortical lesions from published case reports and (2) thalamic lesions with metabolic imaging using 18F- fluorodeoxyglucose positron emission tomography-computed tomography. Functional connectivity between each lesion location and the rest of the brain was assessed using a normative connectome (n = 1,000), and connections specific to CPSP were identified. Metabolic changes specific to CPSP were also identified and related to differences in lesion connectivity. Therapeutic relevance of the network was explored by testing for alignment with existing brain stimulation data and by prospectively targeting the network with repetitive transcranial magnetic stimulation (rTMS) in 7 patients with CPSP.

RESULTS

Lesion locations causing CPSP showed a specific pattern of brain connectivity that was consistent across two independent lesion datasets (spatial r = 0.82, p < 0.0001). Connectivity differences were correlated with postlesion metabolism (r = -0.48, p < 0.001). The topography of this lesion-based pain network aligned with variability in pain improvement across 12 prior neuromodulation targets and across 32 patients who received rTMS to primary motor cortex (p < 0.05). Prospectively targeting this network with rTMS improved CPSP in 6 of 7 patients.

INTERPRETATION

Lesions causing pain are connected to a specific brain network that shows metabolic abnormalities and promise as a neuromodulation target. ANN NEUROL 2022;92:834-845.

Low-Frequency Repetitive Transcranial Magnetic Stimulation in the Early Subacute Phase of Stroke Enhances Angiogenic Mechanisms in Rats

Objective To characterize the repetitive transcranial magnetic stimulation (rTMS) induced changes in angiogenic mechanisms across different brain regions.Methods Seventy-nine adult male Sprague-Dawley rats were subjected to a middle cerebral artery occlusion (day 0) and then treated with 1-Hz, 20-Hz, or sham stimulation of their lesioned hemispheres for 2 weeks. The stimulation intensity was set to 100% of the motor threshold. The neurological function was assessed on days 3, 10, and 17. The infarct volume and angiogenesis were measured by histology, immunohistochemistry, Western blot, and real-time polymerase chain reaction (PCR) assays. Brain tissue was harvested from the ischemic core (IC), ischemic border zone (BZ), and contralateral homologous cortex (CH).Results Optical density of angiopoietin1 and synaptophysin in the IC was significantly greater in the low-frequency group than in the sham group (p=0.03 and p=0.03, respectively). The 1-Hz rTMS significantly increased the level of Akt phosphorylation in the BZ (p<0.05 vs. 20 Hz). Endothelial nitric oxide synthase phosphorylation was increased in the IC (p<0.05 vs. 20 Hz), BZ (p<0.05 vs. 20 Hz), and CH (p<0.05 vs. 20 Hz and p<0.05 vs. sham). Real-time PCR demonstrated that low-frequency stimulation significantly increased the transcriptional activity of the TIE2 gene in the IC (p<0.05).Conclusion Low-frequency rTMS of the ipsilesional hemisphere in the early subacute phase of stroke promotes the expression of angiogenic factors and related genes in the brain, particularly in the injured area.

Gene Expression Profile Changes in the Stimulated Rat Brain Cortex After Repetitive Transcranial Magnetic Stimulation

Repetitive transcranial magnetic stimulation (rTMS) is gaining popularity as a research tool in neuroscience; however, little is known about its molecular mechanisms of action. The present study aimed to investigate the rTMS-induced transcriptomic changes; we performed microarray messenger RNA, micro RNA, and integrated analyses to explore these molecular events. Eight adult male Sprague-Dawley rats were subjected to a single session of unilateral rTMS at 1 Hz (n = 4) or sham (n = 4). The left hemisphere was stimulated for 20 minutes. To evaluate the cumulative effect of rTMS, eight additional rats were assigned to the 1-Hz (n = 4) or sham (n = 4) rTMS groups. The left hemisphere was stimulated for 5 consecutive days using the same protocol. Microarray analysis revealed differentially expressed genes in the rat cortex after rTMS treatment. The overrepresented gene ontology categories included the positive regulation of axon extension, axonogenesis, intracellular transport, and synaptic plasticity after repeated sessions of rTMS. A single session of rTMS primarily induced changes in the early genes, and several miRNAs were significantly related to the mRNAs. Future studies are required to validate the functional significance of selected genes and refine the therapeutic use of rTMS.

Effectiveness of Repetitive Transcranial Magnetic Stimulation on Managing Fibromyalgia: A Systematic Meta-Analysis

OBJECTIVE

In fibromyalgia, central sensitization is a key mechanism, and repetitive transcranial magnetic stimulation (rTMS) has been reported to potentially manage symptoms of fibromyalgia. In this meta-analysis, we evaluated the therapeutic effect of rTMS in patients with fibromyalgia according to stimulation locations and follow-up time points.

METHODS

We searched the MEDLINE, Cochrane, Embase, Scopus, Cumulative Index to Nursing and Allied Health Literature, and Web of Science databases for articles published from January 1, 1990, to August 26, 2021, including randomized controlled studies investigating the effectiveness of rTMS on managing fibromyalgia.

RESULTS

In total, 10 articles and 299 participants were included. High-frequency rTMS on the left primary motor cortex (Lt. M1) had a significant effect on pain reduction immediately and 1-4 weeks after the end of the session but had no significant effect after 5-12 weeks. Additionally, after high-frequency rTMS sessions on the Lt. M1, the effect on patients' quality of life appeared late at 5-12 weeks of follow-up. In contrast, high-frequency rTMS on the left dorsolateral prefrontal cortex (Lt. DLPFC) did not reduce pain from fibromyalgia. The effect on controlling the affective problem was not observed after rTMS treatment on either the Lt. M1 or the Lt. DLPFC.

CONCLUSIONS

High-frequency rTMS had a positive pain-reducing effect immediately and at 1-4 weeks after completion of the rTMS sessions, and the patients' quality of life improved after 5-12 weeks. However, Lt. DLPFC stimulation was not effective in controlling fibromyalgia symptoms.

Changes in the Brain Metabolism Associated with Central Post-Stroke Pain in Hemorrhagic Pontine Stroke: An 18F-FDG-PET Study of the Brain

Central post-stroke pain (CPSP) is an intractable neuropathic pain that can occur following central nervous system injuries. Spino-thalamo-cortical pathway damage contributes to CPSP development. However, brain regions involved in CPSP are unknown and previous studies were limited to supratentorial strokes with cortical lesion involvement. We analyzed the brain metabolism changes associated with CPSP following pontine hemorrhage. Thirty-two patients with isolated pontine hemorrhage were examined; 14 had CPSP, while 18 did not. Brain glucose metabolism was evaluated using 18F-fluorodeoxyglucose-positron emission tomography images. Additionally, regions revealing metabolic correlation with CPSP severity were analyzed. Patients with CPSP showed changes in the brain metabolism in the cerebral cortices and cerebellum. Compared with the control group, the CPSP group showed significant hypometabolism in the contralesional rostral anterior cingulum and ipsilesional primary motor cortex (Puncorrected < 0.001). However, increased brain metabolism was observed in the ipsilesional cerebellum (VI) and contralesional cerebellum (lobule VIIB) (Puncorrected < 0.001). Moreover, increased pain intensity correlated with decreased metabolism in the ipsilesional supplementary motor area and contralesional angular gyrus. This study emphasizes the role of the many different areas of the cortex that are involved in affective and cognitive processing in the development of CPSP.

Facilitatory Effect of Intermittent Repetitive Transcranial Magnetic Stimulation on Perceptual Distortion of the Face

Orofacial pain patients often report that the painful facial area is "swollen" without clinical signs - known as perceptual distortion (PD). The neuromodulatory effect of facilitatory repetitive transcranial magnetic stimulation (rTMS) on PD in healthy individuals was investigated, to provide further support that the primary somatosensory cortex (SI) is involved in facial PD. Participants were allocated to active (n = 26) or sham (n = 26) rTMS group in this case-control study. PD was induced experimentally by injecting local anesthesia (LA) in the right infraorbital region. PD was measured at baseline, 6 min after LA, immediately, 20 and 40 min after rTMS. Intermittent theta-burst stimulation (iTBS) as active rTMS and sham rTMS was applied to the face representation area of SI at 10 min after LA. The magnitude of PD was compared between the groups. The magnitude of PD significantly increased immediately after iTBS compared with sham rTMS (P = .009). The PD was significantly higher immediately after iTBS compared to 6 min after LA (P = .004) in the active rTMS group, but not in the sham rTMS group (P = .054). iTBS applied to a somatotopic-relevant cortical region appears to facilitate facial PD further supporting the involvement of SI in the processing of one´s own face and PD. PERSPECTIVE: This study provides information on neural substrate responsible for processing of perceptual distortion of the face which is speculated to contribute to the chronification of orofacial pain. The findings of this study may aid in mechanism-based management of the condition in orofacial pain disorders and possibly other chronic pain states.

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.

Effects of Repetitive Transcranial Magnetic Stimulation on the Primary Motor Cortex of Individuals with Fibromyalgia: A Systematic Review and Meta-Analysis

The purpose of this study was to quantify the effect of repetitive transcranial magnetic stimulation (rTMS), which is recommended for the improvement of some pain-related symptoms and for antidepressant treatment, on the primary motor cortex (M1) in patients with fibromyalgia (FM). We searched for studies comparing rTMS and sham rTMS in the M1 of FM patients. Pain intensity, quality of life, health status, and depression were compared with or without rTMS for at least 10 sessions. We searched four databases. Quality assessment and quantitative analysis were performed using RevMan 5.4. After screening, five randomized controlled trials of 170 patients with FM were included in the analysis. As a result of the meta-analysis of rTMS on the M1 of individuals with FM, high-frequency rTMS resulted in a significant improvement on quality of life (MD = -2.50; 95% CI: -3.99 to -1.01) compared with sham rTMS. On the other hand, low-frequency rTMS resulted in a significant improvement on health status (MD = 15.02; 95% CI: 5.59 to 24.45). The application of rTMS to the M1 is proposed as an adjunctive measure in the treatment of individuals with FM. Because rTMS has various effects depending on each application site, it is necessary to classify sites or set frequencies as variables.

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.

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.

Effects of repetitive transcranial magnetic stimulation on neuropathic pain: A systematic review and meta-analysis

Neuropathic pain (NP) is a chronic pain condition caused by lesion or disease of the somatosensory nervous system. Repetitive transcranial magnetic stimulation (rTMS) is a neuroregulatory tool that uses pulsed magnetic fields to modulate the cerebral cortex. This review aimed to ascertain the therapeutic effect of rTMS on NP and potential factors regulating the therapeutic effect of rTMS. Database search included Web of Science, Embase, Pubmed, and Cochrane Library from inception to July 2021. Eligible studies included randomized controlled studies of the analgesic effects of rTMS in patients with NP. Thirty-eight studies were included. Random effect analysis showed effect sizes of -0.66 (95 % CI, -0.87 to -0.46), indicating that real rTMS was better than sham condition in reducing pain (P < 0.001). This comprehensive review indicated that stimulation frequency, intervention site, and location of lesion were important factors affecting the therapeutic effect. The findings of this study may guide clinical decisions and future research.

Repetitive Transcranial Magnetic Stimulation for Neuropathic Pain on the Non-Motor Cortex: An Evidence Mapping of Systematic Reviews

OBJECTIVE

This study was aimed to summarize and analyze the quality of the available evidence in systematic reviews (SRs) of repetitive transcranial magnetic stimulation (rTMS) on the non-motor cortex (non-M1) for neuropathic pain (NP) through an evidence mapping approach.

METHODS

We follow the Global Evidence Mapping (GEM) methodology. Searches were conducted in PubMed, EMBASE, Epistemonikos, and the Cochrane Library. The study type was restricted to SRs with or without meta-analysis. All literature published before January 23, 2021, were included. The methodological quality of the included SRs was assessed using A Measurement Tool to Assess Systematic Reviews (AMSTAR-2). Data were extracted according to a defined population-intervention-comparison-outcome (PICO) framework from primary studies that included SRs. The same PICO was categorized into PICOs according to interventions (stimulation target, frequency, number of sessions (short: 1-5 sessions, medium: 5-10 sessions, and long: >10 sessions)) and comparison (sham rTMS or other targets). The evidence mapping was presented in tables and a bubble plot.

RESULTS

A total of 23 SRs were included. According to the AMSTAR-2, 20 SRs scored "very low" in terms of methodological quality, 2 SRs scored "low," and 1 SR scored "high." A total of 17 PICOs were extracted. The dorsolateral prefrontal cortex (DLPFC) is the most studied of the non-motor cortex targets. PICOs of DLPFC, premotor cortex (PMC), frontal cortex, and secondary somatosensory cortex (S2) were mainly categorized with a "potentially better" conclusion. High-frequency (5-20 Hz) rTMS of non-M1 usually lead to "potentially better" conclusions.

CONCLUSIONS

DLPFC, PMC, frontal cortex, and S2 seem to be promising new targets for rTMS treatment of certain NP. Evidence mapping is a useful and reliable methodology to identify and present the existing evidence gap that more research efforts are necessary in order to highlight the optimal stimulation protocols for non-M1 targets and standardize parameters to fill the evidence gaps of rTMS. Further investigation is advised to improve the methodological quality and the reporting process of SRs.

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.

Complex Regional Pain Syndrome. A Comprehensive Review on Neuroplastic Changes Supporting the Use of Non-invasive Neurostimulation in Clinical Settings

Background: Complex regional pain syndrome (CRPS) is a rare debilitating disorder characterized by severe pain affecting one or more limbs. CRPS presents a complex multifactorial physiopathology. The peripheral and sensorimotor abnormalities reflect maladaptive changes of the central nervous system. These changes of volume, connectivity, activation, metabolism, etc., could be the keys to understand chronicization, refractoriness to conventional treatment, and developing more efficient treatments. Objective: This review discusses the use of non-pharmacological, non-invasive neurostimulation techniques in CRPS, with regard to the CRPS physiopathology, brain changes underlying chronicization, conventional approaches to treat CRPS, current evidence, and mechanisms of action of peripheral and brain stimulation. Conclusion: Future work is warranted to foster the evidence of the efficacy of non-invasive neurostimulation in CRPS. It seems that the approach has to be individualized owing to the integrity of the brain and corticospinal function. Non-invasive neurostimulation of the brain or of nerve/muscles/spinal roots, alone or in combination with conventional therapy, represents a fertile ground to develop more efficient approaches for pain management in CRPS.

Exercise-induced hypoalgesia and pain reduction following blood flow restriction: A brief review

OBJECTIVE

To review past literature regarding exercise-induced hypoalgesia and pain reduction following blood flow restriction interventions, and to discuss potential mechanisms as well as future considerations towards the efficacy of blood flow restriction in pain reduction following exercise.

METHODS

To be eligible for inclusion, studies had to include acute exercise, or long-term training interventions, with blood flow restriction, along with including pre and post intervention pain measurements.

RESULTS

A total of 13 studies met the inclusion criteria. Among these 13 studies, 3 studies examined exercise-induced hypoalgesia after an acute bout of resistance exercise with blood flow restriction, and 10 studies investigated pain reduction following long-term blood flow restriction training.

CONCLUSIONS

Existing literature suggests that low load resistance exercise with blood flow restriction may serve as an effective pain management method for those who are unable or unwilling to train with high loads. Several potential mechanisms have been suggested, however, the roles of these mechanisms are still unclear and require further clarification. Future research should consider implementing different methods of blood flow restriction application, and research study design to clarify the utility and efficacy of blood flow restriction as a pain management tool, by itself or in combination with exercise.

Repetitive transcranial magnetic stimulation restores altered functional connectivity of central poststroke pain model monkeys

Central poststroke pain (CPSP) develops after a stroke around the somatosensory pathway. CPSP is hypothesized to be caused by maladaptive reorganization between various brain regions. The treatment for CPSP has not been established; however, repetitive transcranial magnetic stimulation (rTMS) to the primary motor cortex has a clinical effect. To verify the functional reorganization hypothesis for CPSP development and rTMS therapeutic mechanism, we longitudinally pursued the structural and functional changes of the brain by using two male CPSP model monkeys (Macaca fuscata) developed by unilateral hemorrhage in the ventral posterolateral nucleus of the thalamus. Application of rTMS to the ipsilesional primary motor cortex relieved the induced pain of the model monkeys. A tractography analysis revealed a decrease in the structural connectivity in the ipsilesional thalamocortical tract, and rTMS had no effect on the structural connectivity. A region of interest analysis using resting-state functional magnetic resonance imaging revealed inappropriately strengthened functional connectivity between the ipsilesional mediodorsal nucleus of the thalamus and the amygdala, which are regions associated with emotion and memory, suggesting that this may be the cause of CPSP development. Moreover, rTMS normalizes this strengthened connectivity, which may be a possible therapeutic mechanism of rTMS for CPSP.

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

Supplemental Digital Content is Available in the Text.

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.

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.

The effect of rTMS in the management of pain associated with CRPS

BACKGROUND

Therapeutic management of pain in patients with complex regional pain syndrome (CRPS) is challenging. Repetitive transcranial magnetic stimulation (rTMS) has analgesic effects on several types of pain. However, its effect on CRPS has not been elucidated clearly. Therefore, we conducted a meta-analysis of the available clinical studies on rTMS treatment in patients with CRPS.

MATERIALS AND METHODS

A comprehensive literature search was conducted using the PubMed, EMBASE, Cochrane Library, and SCOPUS databases. We included studies published up to February 09, 2020, that fulfilled our inclusion and exclusion criteria. Data regarding measurement of pain using the visual analog scale before and after rTMS treatment were collected to perform the meta-analysis. The meta-analysis was performed using Comprehensive Meta-analysis Version 2.

RESULTS

A total of three studies (one randomized controlled trial and two prospective observational studies) involving 41 patients were included in this meta-analysis. No significant reduction in pain was observed immediately after one rTMS treatment session or immediately after the entire schedule of rTMS treatment sessions (5 or 10 sessions; P > 0.05). However, pain significantly reduced 1 week after the entire schedule of rTMS sessions (P < 0.001).

CONCLUSION

rTMS appears to have a functional analgesic effect in patients with CRPS.

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.

Pilot study of repetitive transcranial magnetic stimulation in patients with chemotherapy-induced peripheral neuropathy

OBJECTIVE

Chemotherapy-induced peripheral neuropathy (CIPN) is one of the intractable long-term side effects of anticancer medications and results in pain and dysesthesia. Repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex has been demonstrated to provide effective relief for intractable neuropathic pain. The objective of this study was to investigate the effects of rTMS treatment on CIPN in cancer patients.

MATERIALS AND METHODS

Eleven female patients with breast cancer or gynecologic cancer (mean age 64.8 [standard deviation 7.8]) who had neuropathic pain and/or peripheral sensory neuropathy, with a minimum two grade severity based on the scale of the National Cancer Institutes' Common Terminology Criteria for Adverse Events (version 4.0) were enrolled. Patients received rTMS (5-Hz; 500 pulses/session; figure-8 coil) on their primary motor cortex corresponding to the target extremity. The intensity of pain and dysesthesia for all extremities was evaluated using a visual analog scale for pain, dysesthesia, and the Japanese version of the short-form McGill Pain Questionnaire 2 (SFMPQ2).

RESULTS

rTMS for target extremity significantly decreased the visual analog scale of pain and dysesthesia. The intensity of pain measured by the SFMPQ2 was also decreased in the target extremity. Regarding non-target extremities, only dysesthesia significantly decreased as a result of rTMS. No adverse events were observed.

CONCLUSION

This is an initial report demonstrating the potential of rTMS for the treatment of CIPN. We suggest rTMS could be potentially beneficial and effective as a treatment for pain and dysesthesia in patients with CIPN.

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.

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.

Effects of continuous theta-burst stimulation of the primary motor and secondary somatosensory areas on the central processing and the perception of trigeminal nociceptive input in healthy volunteers

Supplemental Digital Content is Available in the Text.

Inactivating paired continuous theta-burst stimulation of the primary motor cortex but not on the secondary somatosensory area flattened the relationship between brain activation and stimulus strength while not impacting on the subjective perceptions.

Noninvasive modulation of the activity of pain-related brain regions by means of transcranial magnetic stimulation promises an innovative approach at analgesic treatments. However, heterogeneous successes in pain modulation by setting reversible “virtual lesions” at different brain areas point at unresolved problems including the optimum stimulation site. The secondary somatosensory cortex (S2) has been previously identified to be involved in the perception of pain-intensity differences. Therefore, impeding its activity should impede the coding of the sensory component of pain intensity, resulting in a flattening of the relationship between pain intensity and physical stimulus strength. This was assessed using inactivating spaced continuous theta-burst stimulation (cTBS) in 18 healthy volunteers. In addition, cTBS was applied on the primary motor cortex (M1) shown previously to yield moderate and variable analgesic effects, whereas sham stimulation at both sites served as placebo condition. Continuous theta-burst stimulation flattened the relationship between brain activation and stimulus strength, mainly at S2, the insular cortex, and the postcentral gyrus (16 subjects analyzed). However, these effects were observed after inactivation of M1 while this effect was not observed after inactivation of S2. Nevertheless, both the M1 and the S2-spaced cTBS treatment were not reflected in the ratings of the nociceptive stimuli of different strengths (17 subjects analyzed), contrasting with the clear coding of stimulus strength by these data. Hence, while modulating the central processing of nociceptive input, cTBS failed to produce subjectively relevant changes in pain perception, indicating that the method in the present implementation is still unsuitable for clinical application.

Noninvasive Transcranial Magnetic Brain Stimulation in Stroke

It is likely that transcranial magnetic brain stimulation will be used for the clinical treatment of stroke and stroke-related impairments in the future. The anatomic target and stimulation parameters will likely vary for any clinical focus, be it weakness, pain, or cognitive or communicative dysfunction. Biomarkers may also be useful for identifying patients who will respond best, with a goal to enhance clinical decision making. Combination with drugs or specific types of therapeutic exercise may be necessary to achieve maximal response.

The clinical utility of repetitive transcranial magnetic stimulation in reducing the risks of transitioning from acute to chronic pain in traumatically injured patients

Pain is a multifaceted condition and a major ongoing challenge for healthcare professionals having to treat patients in whom pain put them at risk of developing other conditions. Significant efforts have been invested in both clinical and research settings in an attempt to demystify the mechanisms at stake and develop optimal treatments as well as to reduce individual and societal costs. It is now universally accepted that neuroinflammation and central sensitization are two key underlying factors causing pain chronification as they result from maladaptive central nervous system plasticity. Recent research has shown that the mechanisms of action of repetitive transcranial magnetic stimulation (rTMS) make it a particularly promising avenue in treating various pain conditions. This review will first discuss the contribution of neuroinflammation and central sensitization in the transition from acute to chronic pain in traumatically injured patients. A detailed discussion on how rTMS may allow the restoration from maladaptive plasticity in addition to breaking down the chain of events leading to pain chronification will follow. Lastly, this review will provide a theoretical framework of what might constitute optimal rTMS modalities in dealing with pain symptoms in traumatically injured patients based on an integrated perspective of the physiopathological mechanisms underlying pain.

Non-orthogonal one-step calibration method for robotized transcranial magnetic stimulation

BACKGROUND

Robotized transcranial magnetic stimulation (TMS) combines the benefits of neuro-navigation with automation and provides a precision brain stimulation method. Since the coil will normally remain unmounted between different clinical uses, hand/eye calibration and coil calibration are required before each experiment. Today, these two steps are still separate: hand/eye calibration is performed using methods proposed by Tsai/Lenz or Floris Ernst, and then the coil calibration is carried out based on the traditional TMS experimental step. The process is complex and time-consuming, and traditional coil calibration using a handheld probe is susceptible to greater calibration error.

METHODS

A novel one-step calibration method has been developed to confirm hand/eye and coil calibration results by formulating a matrix equation system and estimating its solution. Hand/eye calibration and coil calibration are performed to confirm the pose relationships of the marker/end effector 'X', probe/end effector 'Y', and robot/world 'Z'. First, the coil is fixed on the end effector of the robot. During the one-step calibration process, a marker is mounted on the top of the coil and a calibration probe is fixed at the actual effective position of the coil. Next, the robot end effector is moved to a series of random positions 'A', the tracking data of marker 'B' and probe 'C' is obtained correspondingly. Then, a matrix equation system AX = ZB and AY = ZC can be acquired, and it is computed using a least-squares approach. Finally, the calibration probe is removed after calibration, while the marker remains fixed to the coil during the TMS experiment. The methods were evaluated based on simulation data and on experimental data from an optical tracking device. We compared our methods with two classical methods: the QR24 method proposed by Floris Ernst and the handheld coil calibration method.

RESULTS

The new methods outperform the QR24 method in the aspect of translational accuracy and performs similarly in the aspect of rotational accuracy, the total translational error decreased more than fifty percent. The new approach also outperforms traditional handheld coil calibration of navigated TMS systems, the total translational error decreased three- to fourfold, and the rotational error decreased six- to eightfold. Furthermore, the convergence speed is improved 16- to 27-fold for the new algorithms.

CONCLUSION

These results suggest that the new method can be used for hand/eye and coil calibration of a robotized TMS system. Two complex steps can be simplified using a least-squares approach.

Proposal for an accurate TMS-MRI co-registration process via 3D laser scanning

An important technical issue in transcranial magnetic stimulation (TMS) usage is how accurately the specific brain areas activated by TMS are assessed. However, in practice, electric field induced in TMS is dispersed and therefore actual estimation is still difficult. As a preliminary step, the projection line which is perpendicular to the TMS stimulation coil beneath the center of the coil must be accurately estimated into the brain. Therefore, we have developed a new TMS-MRI co-registration procedure that employs a 3D laser-scanner system that is very useful for general hand-manipulated TMS, and which easily estimates the TMS projection point onto the brain. The proposed system accurately captures the positional relationship between the TMS coil and anatomical images. The results of 3D image processing revealed that the registration error at each stage was kept within the submillimeter level. In addition, a motor evoked potential experiment examining the right finger motor area revealed that understandable responses were obtained when stimulation was targeted to the three different motor areas according to Penfield's map. 3D laser scanning is a technique of substantial recent interest for anatomical co-registration. The proposed method demonstrated submillimeter level accuracy of TMS-MRI co-registration.

Less Might Be More: Conduction Failure as a Factor Possibly Limiting the Efficacy of Higher Frequencies in rTMS Protocols

Introduction: rTMS has been proven effective in the treatment of neuropsychiatric conditions, with class A (definite efficacy) evidence for treatment of depression and pain (Lefaucheur et al., 2014). The efficacy in stimulation protocols is, however, quite heterogeneous. Saturation of neuronal firing by HFrTMS without allowing time for recovery may lead to neuronal response failures (NRFs) that compromise the efficacy of stimulation with higher frequencies.

Objectives: To examine the efficacy of different rTMS temporal stimulation patterns focusing on a possible upper stimulation limit related to response failures. Protocol patterns were derived from published clinical studies on therapeutic rTMS for depression and pain. They were compared with conduction failures in cell cultures.

Methodology: From 57 papers using protocols rated class A for depression and pain (Lefaucheur et al., 2014) we extracted Inter-train interval (ITI), average frequency, total duration and total number of pulses and plotted them against the percent improvement on the outcome scale. Specifically, we compared 10 Hz trains with ITIs of 8 s (protocol A) and 26 s (protocol B) in vitro on cultured cortical neurons.

Results: In the in vitro experiments, protocol A with 8-s ITIs resulted in more frequent response failures, while practically no response failures occurred with protocol B (26-s intervals). The HFrTMS protocol analysis exhibited no significant effect of ITIs on protocol efficiency.

Discussion: In the neuronal culture, longer ITIs appeared to allow the neuronal response to recover. In the available human dataset on both depression and chronic pain, data concerning shorter ITIs is does not allow a significant conclusion.

Significance: NRF may interfere with the efficacy of rTMS stimulation protocols when the average stimulation frequency is too high, proposing ITIs as a variable in rTMS protocol efficacy. Clinical trials are necessary to examine effect of shorter ITIs on the clinical outcome in a controlled setting.

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.

Repetitive transcranial magnetic stimulation accuracy as a spinal cord stimulation outcome predictor in patients with neuropathic pain

OBJECT

Spinal cord stimulation (SCS) is an effective albeit invasive and relatively expensive treatment of neuropathic pain. Repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex (M1) is a non-invasive treatment of neuropathic pain. The aim of the current study was to investigate whether rTMS can predict the successful outcome of SCS.

METHODS

The study population consisted of 22 patients with neuropathic pain who had undergone SCS and rTMS. We conducted statistical analyses to identify the factors that predict pain reduction following SCS.

RESULTS

Multiple regression analyses showed that only degree of pain relief following rTMS was statistically correlated with success in SCS; on the other hand, age, sex, lesion location, pain duration and laterality, and targeted extremities were not correlated. Using receiver-operating characteristic (ROC) curve analyses of the pain relief following rTMS, the diagnostic sensitivity for successful SCS was 0.60 and the specificity was 0.83.

CONCLUSIONS

The degree of pain relief following rTMS over M1 is a significant prognostic factor of SCS outcome in patients with intractable neuropathic pain.

SIGNIFICANCE

The current study provides evidence showing that rTMS, a non-invasive and relatively easy to administer procedure, may aid in the selection of suitable candidates for SCS treatment.