Motor cortex rTMS restores defective intracortical inhibition in chronic neuropathic pain

Motor Cortex Stimulation for Pain Relief: Do Corollary Discharges Play a Role?

Both invasive and non-invasive motor cortex stimulation techniques have been successfully employed in the treatment of chronic pain, but the precise mechanism of action of such treatments is not fully understood. It has been hypothesized that a mismatch of normal interaction between motor intention and sensory feedback may result in central pain. Sensory feedback may come from peripheral nerves, vision and also from corollary discharges originating from the motor cortex itself. Therefore, a possible mechanism of action of motor cortex stimulation might be corollary discharge reinforcement, which could counterbalance sensory feedback deficiency. In other instances, primary deficiency in the production of corollary discharges by the motor cortex might be the culprit and stimulation of cortical motor areas might then be beneficial by enhancing production of such discharges. Here we review evidence for a possible role of motor cortex corollary discharges upon both the pathophysiology and the response to motor cortex stimulation of different types of chronic pain. We further suggest that the right dorsolateral prefrontal cortex (DLPC), thought to constantly monitor incongruity between corollary discharges, vision and proprioception, might be an interesting target for non-invasive neuromodulation in cases of chronic neuropathic pain.

Experimental tonic hand pain modulates the corticospinal plasticity induced by a subsequent hand deafferentation

Sensorimotor reorganization is believed to play an important role in the development and maintenance of phantom limb pain, but pain itself might modulate sensorimotor plasticity induced by deafferentation. Clinical and basic research support this idea, as pain prior to amputation increases the risk of developing post-amputation pain. The aim of this study was to examine the influence of experimental tonic cutaneous hand pain on the plasticity induced by temporary ischemic hand deafferentation. Sixteen healthy subjects participated in two experimental sessions (Pain, No Pain) in which transcranial magnetic stimulation was used to assess corticospinal excitability in two forearm muscles (flexor carpi radialis and flexor digitorum superficialis) before (T0, T10, T20, and T40) and after (T60 and T75) inflation of a cuff around the wrist. The cuff was inflated at T45 in both sessions and in the Pain session capsaicin cream was applied on the dorsum of the hand at T5. Corticospinal excitability was significantly greater during the Post-inflation phase (p=0.002) and increased similarly in both muscles (p=0.861). Importantly, the excitability increase in the Post-inflation phase was greater for the Pain than the No-Pain condition (p=0.006). Post-hoc analyses revealed a significant difference between the two conditions during the Post-inflation phase (p=0.030) but no difference during the Pre-inflation phase (p=0.601). In other words, the corticospinal facilitation was greater when pain was present prior to cuff inflation. These results indicate that pain can modulate the plasticity induced by another event, and could partially explain the sensorimotor reorganization often reported in chronic pain populations.

Influence of paravertebral muscles training on brain plasticity and postural control in chronic low back pain

BACKGROUND AND PURPOSE

Isometric activation (ISOM) of deep multifidi muscles (MF) can influence postural adjustments and primary motor cortex (M1) function in chronic low back pain (CLBP). In order to better understand how ISOM impacts on CLBP condition, the present study contrasted ISOM after-effects on M1 function, MF postural activation and pain with another training, the global activation of paravertebral muscles (GLOB, hip extension). The main objective of this study was to compare the effects of ISOM and GLOB (3-week training each) on MF postural activation and M1 function in a CLBP population.

METHODS

Twenty-four people with CLBP were randomly allocated to ISOM and GLOB groups for a 3-week daily practice. Pre/post-training after-effects were assessed by the onset of superficial MF (MF-S) activation during ballistic limb movements (bilateral shoulder flexion in standing; unilateral hip extension in prine lying), MF-S corticomotor control tested by transcranial magnetic stimulation of M1, and assessment of pain, kinesiophobia and disability by standardized questionnaires.

RESULTS

Both ISOM and GLOB improved pain and disability. However, only ISOM influenced M1 function (decreased corticospinal excitability and increased intracortical inhibition), fastened MF-S postural activation and decreased kinesiophobia.

CONCLUSIONS

Changes of corticospinal excitability and of MF-S postural adjustments suggest that ISOM better influenced brain plasticity. Future studies should further test whether our novel findings relate to an influence of the exercises on the lumbopelvic control of different muscles and on cognitive function. Clinically, individual's evaluation remains warranted before prescribing one or the other of these two conventional exercises for reducing pain.

IMPLICATIONS

This original study presents how motor control exercises can influence brain plasticity and postural control in chronic low back pain. This knowledge will impact on the decision of clinicians to prescribe specific exercises with a view of improving motor control in this musculoskeletal condition.

The effects of add-on non-invasive brain stimulation in fibromyalgia: a meta-analysis and meta-regression of randomized controlled trials

OBJECTIVES

The effects of non-invasive brain stimulation (NBS), including repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (TDCS), in treating FM remain inconclusive. The aim of this study was to investigate present evidence of using NBS as an add-on treatment in treating FM.

METHODS

We conducted a database search of the Medline, Embase, PsycINFO and Cochrane Library electronic databases, from inception to July 2015, to analyse randomized controlled trials of NBS in treating FM. A total of 16 studies were included in the current meta-analysis.

RESULTS

The pooled mean effect sizes of the 16 included studies revealed significant favourable effects of NBS. The weighted mean effect size in reducing pain, depression, fatigue, sleep disturbance and tender points and improving general health/function were 0.667 (95% CI 0.446, 0.889), 0.322 (95% CI 0.140, 0.504), 0.511 (95% CI 0.247, 0.774), 0.682 (95% CI 0.350, 1.014), 0.867 (95% CI 0.310, 1.425) and 0.473 (95% CI 0.285, 0.661), respectively. rTMS stimulation yielded a greater effect size compared with that of TDCS (effect size 0.698 and 0.568, respectively; P < 0.0001). The primary motor cortex (M1) stimulation yielded a subtle greater effect size in pain reduction compared with that of the dorsolateral prefrontal cortex (effect size 0.709 and 0.693, respectively; P < 0.0001). No linear relationships were found between the effect sizes and treatment regimens and dose. Most of reported adverse effects were minor.

CONCLUSIONS

Both rTMS and TDCS may be feasible and safe modalities for treating FM. The general effects of rTMS and TDCS are compatible in FM patients. M1 stimulation may be better in pain reduction and the dorsolateral prefrontal cortex may be better in depression improvement.

Transcranial magnetic stimulation as a new tool to control pain perception

Treatment for chronic pain is frequently unsuccessful or characterized by side-effects. The high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) has been suggested in the management of refractory chronic pain. Various studies have shown that HF-rTMS sessions of long-duration applied at primary motor cortex induce pain relief through mechanisms of plastic changes. Efficacy of rTMS mostly depends on stimulation parameters, but this aspect requires better characterization. A rationale to target other cortical areas exists. Current data are promising, but a careful analysis of stimulation settings and maintenance treatment design are need.

Transcranial Direct Current Stimulation Combined with Aerobic Exercise to Optimize Analgesic Responses in Fibromyalgia: A Randomized Placebo-Controlled Clinical Trial

Fibromyalgia is a chronic pain syndrome that is associated with maladaptive plasticity in neural central circuits. One of the neural circuits that are involved in pain in fibromyalgia is the primary motor cortex. We tested a combination intervention that aimed to modulate the motor system: transcranial direct current stimulation (tDCS) of the primary motor cortex (M1) and aerobic exercise (AE). In this phase II, sham-controlled randomized clinical trial, 45 subjects were assigned to 1 of 3 groups: tDCS + AE, AE only, and tDCS only. The following outcomes were assessed: intensity of pain, level of anxiety, quality of life, mood, pressure pain threshold, and cortical plasticity, as indexed by transcranial magnetic stimulation. There was a significant effect for the group-time interaction for intensity of pain, demonstrating that tDCS/AE was superior to AE [F (13, 364) = 2.25, p = 0.007] and tDCS [F (13, 364) = 2.33, p = 0.0056] alone. Post-hoc adjusted analysis showed a difference between tDCS/AE and tDCS group after the first week of stimulation and after 1 month intervention period (p = 0.02 and p = 0.03, respectively). Further, after treatment there was a significant difference between groups in anxiety and mood levels. The combination treatment effected the greatest response. The three groups had no differences regarding responses in motor cortex plasticity, as assessed by TMS. The combination of tDCS with aerobic exercise is superior compared with each individual intervention (cohen's d effect sizes > 0.55). The combination intervention had a significant effect on pain, anxiety and mood. Based on the similar effects on cortical plasticity outcomes, the combination intervention might have affected other neural circuits, such as those that control the affective-emotional aspects of pain.

TRIAL REGISTRATION

(www.ClinicalTrials.gov), identifier NTC02358902.

Viewing the body modulates both pain sensations and pain responses

Viewing the body can influence pain perception, even when vision is non-informative about the noxious stimulus. Prior studies used either continuous pain rating scales or pain detection thresholds, which cannot distinguish whether viewing the body changes the discriminability of noxious heat intensities or merely shifts reported pain levels. In Experiment 1, participants discriminated two intensities of heat-pain stimulation. Noxious stimuli were delivered to the hand in darkness immediately after participants viewed either their own hand or a non-body object appearing in the same location. The visual condition varied randomly between trials. Discriminability of the noxious heat intensities (d′) was lower after viewing the hand than after viewing the object, indicating that viewing the hand reduced the information about stimulus intensity available within the nociceptive system. In Experiment 2, the hand and the object were presented in separate blocks of trials. Viewing the hand shifted perceived pain levels irrespective of actual stimulus intensity, biasing responses toward ‘high pain’ judgments. In Experiment 3, participants saw the noxious stimulus as it approached and touched their hand or the object. Seeing the pain-inducing event counteracted the reduction in discriminability found when viewing the hand alone. These findings show that viewing the body can affect both perceptual processing of pain and responses to pain, depending on the visual context. Many factors modulate pain; our study highlights the importance of distinguishing modulations of perceptual processing from modulations of response bias.

Potential Mechanisms Supporting the Value of Motor Cortex Stimulation to Treat Chronic Pain Syndromes

Throughout the first years of the twenty-first century, neurotechnologies such as motor cortex stimulation (MCS), transcranial magnetic stimulation (TMS), and transcranial direct current stimulation (tDCS) have attracted scientific attention and been considered as potential tools to centrally modulate chronic pain, especially for those conditions more difficult to manage and refractory to all types of available pharmacological therapies. Interestingly, although the role of the motor cortex in pain has not been fully clarified, it is one of the cortical areas most commonly targeted by invasive and non-invasive neuromodulation technologies. Recent studies have provided significant advances concerning the establishment of the clinical effectiveness of primary MCS to treat different chronic pain syndromes. Concurrently, the neuromechanisms related to each method of primary motor cortex (M1) modulation have been unveiled. In this respect, the most consistent scientific evidence originates from MCS studies, which indicate the activation of top-down controls driven by M1 stimulation. This concept has also been applied to explain M1-TMS mechanisms. Nevertheless, activation of remote areas in the brain, including cortical and subcortical structures, has been reported with both invasive and non-invasive methods and the participation of major neurotransmitters (e.g., glutamate, GABA, and serotonin) as well as the release of endogenous opioids has been demonstrated. In this critical review, the putative mechanisms underlying the use of MCS to provide relief from chronic migraine and other types of chronic pain are discussed. Emphasis is placed on the most recent scientific evidence obtained from chronic pain research studies involving MCS and non-invasive neuromodulation methods (e.g., tDCS and TMS), which are analyzed comparatively.

Corticomotor control of lumbar multifidus muscles is impaired in chronic low back pain: concurrent evidence from ultrasound imaging and double-pulse transcranial magnetic stimulation

Chronic low back pain (CLBP) is often associated with impaired control of deep trunk muscles and reorganization of the primary motor areas (M1). Precisely, functional changes of the lumbar multifidus muscles (MF) involved in spine stability may be of special interest in rehabilitation. Therefore, we tested MF corticomotor control using double transcranial magnetic stimulation (TMS) paradigms for the first time in this muscle and examined its link with MF volitional activation. Eleven individuals with lateralized CLBP and 13 pain-free participants were recruited. Ultrasound imaging enabled measurement of MF volitional isometric contraction in prone lying. TMS of MF M1 area was used to test hemispheric excitability and mechanisms in relation to motor programming, i.e., active motor threshold (AMT), amplitude of motor-evoked potentials and short-interval intracortical inhibition (SICI) and facilitation (SICF). In CLBP, SICI level was lower in the left hemisphere and MF volitional contraction was not related to AMT (M1 excitability), conversely to what was observed in the pain-free group. No other between-group difference was detected. These original findings support a plasticity of cortical maps controlling paravertebral muscles and likely including a different motor strategy for the control of MF. Changes of M1 function may thus underlie impaired motor control of lumbopelvic spine and pain persistence in CLBP.

Disinhibition of the primary somatosensory cortex in patients with fibromyalgia

Fibromyalgia (FM) is a chronic widespread pain condition linked to central sensitization. Altered excitability of sensorimotor cortex has been proposed as an underlying pathology of FM. This study aimed to investigate intracortical excitability of the primary somatosensory cortex (S1) and its potential role in clinical pain in patients with FM. Somatosensory evoked magnetic fields were recorded in 17 right-handed females with FM and 21 age-, sex-, and handedness-matched healthy control subjects. Paired-pulse median nerve stimulation was delivered to the left and right wrist. We assessed the peak-to-peak amplitudes of the N20m-P35m and peak amplitude of each N20m and P35m component. Paired-pulse suppression (PPS) of the second response was quantified as the ratio of the amplitudes of the second to the first response. Patients with FM displayed significantly higher PPS ratio for the N20m-P35m in both hemispheres, indicating reduced intracortical inhibition in the S1. Notably, PPS ratio for the P35m was higher in patients with FM than in healthy controls, whereas no differences were apparent in PPS ratio for the N20m in both hemispheres. For both the N20m-P35m and the P35m in the left hemisphere, PPS ratios were positively associated with the sensory pain on the short-form McGill Pain Questionnaire. This study demonstrated that intracortical inhibition in the S1 is compromised bilaterally in patients with FM, and the extent of disinhibition can be closely associated with increased clinical pain. Our results suggest that changes of intracortical inhibition of the S1 may contribute to the pathophysiology of FM pain.

The Neurophysiologist Perspective into MS Plasticity

Multiple sclerosis (MS) is a frequent, highly debilitating inflammatory demyelinating disease, starting to manifest in early adulthood and presenting a wide variety of symptoms, which are often resistant to pharmacological treatments. Cortical dysfunctions have been demonstrated to be key components of MS condition, and plasticity of the corticospinal motor system is highly involved in major MS symptoms, such as fatigue, spasticity, or pain. Cortical dysfunction in MS can be studied with neurophysiological tools, such as electroencephalography (EEG) and related techniques (evoked potentials) or transcranial magnetic stimulation (TMS). These techniques are now widely used to provide essential elements of MS diagnosis and can also be used to modulate plasticity. Indeed, the recent development of non-invasive brain stimulation techniques able to induce cortical plasticity, such as repetitive TMS or transcranial direct current stimulation, has brought promising results as add-on treatments. In this review, we will focus on the use of these tools (EEG and TMS) to study plasticity in MS and on the major techniques used to modulate plasticity in MS.

Optimal Strategies for Reporting Pain in Clinical Trials and Systematic Reviews: Recommendations from an OMERACT 12 Workshop

OBJECTIVE

Pain is a patient-important outcome, but current reporting in randomized controlled trials and systematic reviews is often suboptimal, impeding clinical interpretation and decision making.

METHODS

A working group at the 2014 Outcome Measures in Rheumatology (OMERACT 12) was convened to provide guidance for reporting treatment effects regarding pain for individual studies and systematic reviews.

RESULTS

For individual trials, authors should report, in addition to mean change, the proportion of patients achieving 1 or more thresholds of improvement from baseline pain (e.g., ≥ 20%, ≥ 30%, ≥ 50%), achievement of a desirable pain state (e.g., no worse than mild pain), and/or a combination of change and state. Effects on pain should be accompanied by other patient-important outcomes to facilitate interpretation. When pooling data for metaanalysis, authors should consider converting all continuous measures for pain to a 100 mm visual analog scale (VAS) for pain and use the established, minimally important difference (MID) of 10 mm, and the conventionally used, appreciably important differences of 20 mm, 30 mm, and 50 mm, to facilitate interpretation. Effects ≤ 0.5 units suggest a small or very small effect. To further increase interpretability, the pooled estimate on the VAS should also be transformed to a binary outcome and expressed as a relative risk and risk difference. This transformation can be achieved by calculating the probability of experiencing a treatment effect greater than the MID and the thresholds for appreciably important differences in pain reduction in the control and intervention groups.

CONCLUSION

Presentation of relative effects regarding pain will facilitate interpretation of treatment effects.

Ocular neuropathic pain

As the biological alarm of impending or actual tissue damage, pain is essential for our survival. However, when it is initiated and/or sustained by dysfunctional elements in the nociceptive system, it is itself a disease known as neuropathic pain. While the critical nociceptive system provides a number of protective functions, it is unique in its central role of monitoring, preserving and restoring the optical tear film in the face of evaporative attrition without which our vision would be non-functional. Meeting this existential need resulted in the evolution of the highly complex, powerful and sensitive dry eye alarm system integrated in the peripheral and central trigeminal sensory network. The clinical consequences of corneal damage to these nociceptive pathways are determined by the type and location of its pathological elements and can range from the spectrum known as dry eye disease to the centalised oculofacial neuropathic pain syndrome characterised by a striking disparity between the high intensity of symptoms and paucity of external signs. These changes parallel those observed in somatic neuropathic pain. When seen through the neuroscience lens, diseases responsible for inadequately explained chronic eye pain (including those described as dry eye) can take on new meanings that may clarify long-standing enigmas and point to new approaches for developing preventive, symptomatic and disease-modifying interventions for these currently refractory disorders.

Mental imagery-induced attention modulates pain perception and cortical excitability

Background

Mental imagery is a powerful method of altering brain activity and behavioral outcomes, such as performance of cognition and motor skills. Further, attention and distraction can modulate pain-related neuronal networks and the perception of pain. This exploratory study examined the effects of mental imagery-induced attention on pressure pain threshold and cortical plasticity using transcranial magnetic stimulation (TMS). This blinded, randomized, and parallel-design trial comprised 30 healthy right-handed male subjects. Exploratory statistical analyses were performed using ANOVA and t-tests for pain and TMS assessments. Pearson’s correlation was used to analyze the association between changes in pain threshold and cortical excitability.

Results

In the analysis of pain outcomes, there was no significant interaction effect on pain between group versus time. In an exploratory analysis, we only observed a significant effect of group for the targeted left hand (ANOVA with pain threshold as the dependent variable and time and group as independent variables). Although there was only a within-group effect of mental imagery on pain, further analyses showed a significant positive correlation of changes in pain threshold and cortical excitability (motor-evoked potentials via TMS).

Conclusions

Mental imagery has a minor effect on pain modulation in healthy subjects. Its effects appear to differ compared with chronic pain, leading to a small decrease in pain threshold. Assessments of cortical excitability confirmed that these effects are related to the modulation of pain-related cortical circuits. These exploratory findings suggest that neuronal plasticity is influenced by pain and that the mental imagery effects on pain depend on the state of central sensitization.

Non-invasive electrical and magnetic stimulation of the brain, spinal cord, roots and peripheral nerves: Basic principles and procedures for routine clinical and research application. An updated report from an I.F.C.N. Committee

These guidelines provide an up-date of previous IFCN report on “Non-invasive electrical and magnetic stimulation of the brain, spinal cord and roots: basic principles and procedures for routine clinical application” (Rossini et al., 1994). A new Committee, composed of international experts, some of whom were in the panel of the 1994 “Report”, was selected to produce a current state-of-the-art review of non-invasive stimulation both for clinical application and research in neuroscience.

Since 1994, the international scientific community has seen a rapid increase in non-invasive brain stimulation in studying cognition, brain–behavior relationship and pathophysiology of various neurologic and psychiatric disorders. New paradigms of stimulation and new techniques have been developed. Furthermore, a large number of studies and clinical trials have demonstrated potential therapeutic applications of non-invasive brain stimulation, especially for TMS. Recent guidelines can be found in the literature covering specific aspects of non-invasive brain stimulation, such as safety (Rossi et al., 2009), methodology (Groppa et al., 2012) and therapeutic applications (Lefaucheur et al., 2014).

This up-dated review covers theoretical, physiological and practical aspects of non-invasive stimulation of brain, spinal cord, nerve roots and peripheral nerves in the light of more updated knowledge, and include some recent extensions and developments.

Treatment of Chronic Facial Pain Including Cluster Headache by Repetitive Transcranial Magnetic Stimulation of the Motor Cortex With Maintenance Sessions: A Naturalistic Study

OBJECTIVE

To assess the long-term maintenance of analgesia induced by high-frequency repetitive transcranial magnetic stimulation (rTMS) of the motor cortex contralateral to pain in a naturalistic study of patients with chronic refractory facial pain.

METHODS

55 patients were included (cluster headache, n = 19; trigeminal neuropathic pain, n = 21; atypical facial pain, n = 15). The rTMS protocol consisted of an "induction phase" of one daily rTMS session for five days per week during two consecutive weeks, followed by a "maintenance phase" of two sessions during one week, then one session in weeks 4 and 6, and a monthly session for the next five months. In a subset of patients, navigated targeting was performed and session duration was shortened from 20-min to 10-min (with the same number of 2000 pulses per session). The analgesic effect of rTMS was assessed on a 0-10 visual numerical scale from 15 to 180 days after treatment initiation.

RESULTS

All pain measures significantly decreased from baseline to D15: the intensity of permanent pain (5.2 ± 1.6 to 3.2 ± 1.9) and paroxysmal pain (8.6 ± 1.5 to 4.5 ± 3.4), as well as the daily number of painful attacks (5.6 ± 3.1 to 2.3 ± 3.1). The percentage of responders (defined as pain score decrease ≥30%) was 73% at D15 and dropped to 40% at D180. The analgesic effect was similar regardless of the type of pain and was significantly lower when session duration was shortened, irrespective of the number of pulses.

CONCLUSION

This long-term maintenance rTMS protocol can be a therapeutic option in the clinical management of patients with chronic refractory facial pain, including cluster headache. However, only part of the patients respond to this technique and session duration should not be reduced.

Motor Cortex Reorganization and Impaired Function in the Transition to Sustained Muscle Pain

Primary motor cortical (M1) adaptation has not been investigated in the transition to sustained muscle pain. Daily injection of nerve growth factor (NGF) induces hyperalgesia reminiscent of musculoskeletal pain and provides a novel model to study M1 in response to progressively developing muscle soreness. Twelve healthy individuals were injected with NGF into right extensor carpi radialis brevis (ECRB) on Days 0 and 2 and with hypertonic saline on Day 4. Quantitative sensory and motor testing and assessment of M1 organization and function using transcranial magnetic stimulation were performed prior to injection on Days 0, 2, and 4 and again on Day 14. Pain and disability increased at Day 2 and increased further at Day 4. Reorganization of M1 was evident at Day 4 and was characterized by increased map excitability. These changes were accompanied by reduced intracortical inhibition and increased intracortical facilitation. Interhemispheric inhibition was reduced from the "affected" to the "unaffected" hemisphere on Day 4, and this was associated with increased pressure sensitivity in left ECRB. These data provide the first evidence of M1 adaptation in the transition to sustained muscle pain and have relevance for the development of therapies that seek to target M1 in musculoskeletal pain.

An MRI-compatible, ultra-thin, flexible stimulator array for functional neuroimaging by direct stimulation of the rat brain

We developed an MRI-compatible, ultra-thin, flexible stimulator array for the rat brain and performed functional MRI (fMRI) acquisition during direct electrical stimulation of the brain. This technique measured brain activity evoked by direct stimulation of the motor and the somatosensory cortex. In order to avoid MR signal loss due to interferences with the main static field and RF field in the MRI system, the stimulator array was made from a non-magnetic gold electrode of 100-nm thickness on a 2-um-thick parylene substrate. By using this stimulator array, MR images without signal loss around conducting electrode pads were acquired, and fMRI acquisition during concurrent electrical stimulation of the cerebral cortex was achieved. Neuronal activity propagated to distant brain areas from the stimulated motor cortex. Positive blood oxygenation level dependent (BOLD) signals were observed with direct stimulation of the motor cortex, while negative BOLD signals were observed with direct stimulation of the somatosensory cortex. Interestingly, the pattern of brain activity evoked by direct stimulation of the somatosensory cortex was different from that evoked by electrical stimulation of the forepaw.

Non-pharmacological interventions for chronic pain in people with spinal cord injury

BACKGROUND

Chronic pain is frequent in persons living with spinal cord injury (SCI). Conventionally, the pain is treated pharmacologically, yet long-term pain medication is often refractory and associated with side effects. Non-pharmacological interventions are frequently advocated, although the benefit and harm profiles of these treatments are not well established, in part because of methodological weaknesses of available studies.

OBJECTIVES

To critically appraise and synthesise available research evidence on the effects of non-pharmacological interventions for the treatment of chronic neuropathic and nociceptive pain in people living with SCI.

SEARCH METHODS

The search was run on the 1st March 2011. We searched the Cochrane Injuries Group's Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (OvidSP), Embase (OvidSP), PsycINFO (OvidSP), four other databases and clinical trials registers. In addition, we manually searched the proceedings of three major scientific conferences on SCI. We updated this search in November 2014 but these results have not yet been incorporated.

SELECTION CRITERIA

Randomised controlled trials of any intervention not involving intake of medication or other active substances to treat chronic pain in people with SCI.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed risk of bias in the included studies. The primary outcome was any measure of pain intensity or pain relief. Secondary outcomes included adverse events, anxiety, depression and quality of life. When possible, meta-analyses were performed to calculate standardised mean differences for each type of intervention.

MAIN RESULTS

We identified 16 trials involving a total of 616 participants. Eight different types of interventions were studied. Eight trials investigated the effects of electrical brain stimulation (transcranial direct current stimulation (tDCS) and cranial electrotherapy stimulation (CES); five trials) or repetitive transcranial magnetic stimulation (rTMS; three trials). Interventions in the remaining studies included exercise programmes (three trials); acupuncture (two trials); self-hypnosis (one trial); transcutaneous electrical nerve stimulation (TENS) (one trial); and a cognitive behavioural programme (one trial). None of the included trials were considered to have low overall risk of bias. Twelve studies had high overall risk of bias, and in four studies risk of bias was unclear. The overall quality of the included studies was weak. Their validity was impaired by methodological weaknesses such as inappropriate choice of control groups. An additional search in November 2014 identified more recent studies that will be included in an update of this review.For tDCS the pooled mean difference between intervention and control groups in pain scores on an 11-point visual analogue scale (VAS) (0-10) was a reduction of -1.90 units (95% confidence interval (CI) -3.48 to -0.33; P value 0.02) in the short term and of -1.87 (95% CI -3.30 to -0.45; P value 0.01) in the mid term. Exercise programmes led to mean reductions in chronic shoulder pain of -1.9 score points for the Short Form (SF)-36 item for pain experience (95% CI -3.4 to -0.4; P value 0.01) and -2.8 pain VAS units (95% CI -3.77 to -1.83; P value < 0.00001); this represented the largest observed treatment effects in the included studies. Trials using rTMS, CES, acupuncture, self-hypnosis, TENS or a cognitive behavioural programme provided no evidence that these interventions reduce chronic pain. Ten trials examined study endpoints other than pain, including anxiety, depression and quality of life, but available data were too scarce for firm conclusions to be drawn. In four trials no side effects were reported with study interventions. Five trials reported transient mild side effects. Overall, a paucity of evidence was found on any serious or long-lasting side effects of the interventions.

AUTHORS' CONCLUSIONS

Evidence is insufficient to suggest that non-pharmacological treatments are effective in reducing chronic pain in people living with SCI. The benefits and harms of commonly used non-pharmacological pain treatments should be investigated in randomised controlled trials with adequate sample size and study methodology.

Repetitive transcranial magnetic stimulation in chronic pain: a review of the literature

OBJECTIVE

To review the literature on the analgesic effects of repetitive transcranial magnetic stimulation (rTMS) in chronic pain according to different pain syndromes and stimulation parameters.

DATA SOURCES

Publications on rTMS and chronic pain were searched in PubMed and Google Scholar using the following key words: chronic pain, analgesia, transcranial magnetic stimulation, neuropathic pain, fibromyalgia, and complex regional pain syndrome.

STUDY SELECTION

This review only included double-blind, controlled studies with >10 participants in each arm that were published from 1996 to 2014 and written in English. Studies with relevant information for the understanding of the effects of rTMS were also cited.

DATA EXTRACTION

The following data were retained: type of pain syndrome, type of study, coil type, target, stimulation intensity, frequency, number of pulses, orientation of induced current, number of session, and a brief summary of intervention outcomes.

DATA SYNTHESIS

A total of 33 randomized trials were found. Many studies reported significant pain relief by rTMS, especially high-frequency stimulation over the primary motor cortex performed in consecutive treatment sessions. Pain relief was frequently >30% compared with control treatment. Neuropathic pain, fibromyalgia, and complex regional pain syndrome were the pain syndromes more frequently studied. However, among all published studies, only a few performed repetitive sessions of rTMS.

CONCLUSIONS

rTMS has potential utility in the management of chronic pain; however, studies using maintenance sessions of rTMS and assessing the effects of rTMS on the different aspects of chronic pain are needed to provide a more solid basis for its clinical application for pain relief.

Corticospinal and intracortical excitability of the quadriceps in patients with knee osteoarthritis

Deficits in voluntary activation of the quadriceps muscle are characteristic of knee osteoarthritis (OA), contributing to the quadriceps weakness that is also a hallmark of the disease. The mechanisms underlying this central activation deficit (CAD) are unknown, although cortical mechanisms may be involved. Here, we utilize transcranial magnetic stimulation (TMS) to assess corticospinal and intracortical excitability in patients with knee OA and in a comparably aged group of healthy older adults, to quantify group differences, and to examine associations between TMS measures and pain, quadriceps strength, and CAD. Seventeen patients with knee OA and 20 healthy controls completed testing. Motor evoked potentials were measured at the quadriceps by superficial electromyographic recordings. Corticospinal excitability was assessed by measuring resting motor threshold (RMT) to TMS stimulation of the quadriceps representation at primary motor cortex, and intracortical excitability was assessed via paired-pulse paradigms for short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF). No statistically significant differences between patients with knee OA and healthy controls were found for RMT, SICI or ICF measures (p > 0.05). For patients with knee OA, there were significant associations observed between pain and RMT, as well as between pain and ICF. No associations were observed between CAD and measures of corticospinal or intracortical excitability. These data suggest against direct involvement of corticospinal or intracortical pathways within primary motor cortex in the mechanisms of CAD. However, pain is implicated in the neural mechanisms of quadriceps motor control in patients with knee OA.

Transcranial magnetic stimulation for chronic pain

Current data suggest that transcranial magnetic stimulation (TMS) has the potential to be an effective and complimentary treatment modality for patients with chronic neuropathic pain syndromes. The success of TMS for pain relief depends on the parameters of the stimulation delivered, the location of neural target, and duration of treatment. TMS can be used to excite or inhibit underlying neural tissue that depends on long-term potentiation and long-term depression, respectively. Long-term randomized controlled studies are warranted to establish the efficacy of repetitive TMS in patients with various chronic pain syndromes.

Alterations in central motor representation increase over time in individuals with rotator cuff tendinopathy

OBJECTIVE

To investigate whether rotator cuff tendinopathy leads to changes in central motor representation of a rotator cuff muscle, and to assess whether such changes are related to pain intensity, pain duration, and physical disability.

METHODS

Using transcranial magnetic stimulation, motor representation of infraspinatus muscle was assessed bilaterally in patients with unilateral rotator cuff tendinopathy.

RESULTS

Active motor threshold is significantly larger for the affected shoulder comparatively to the unaffected shoulder (n=39, p=0.01), indicating decreased corticospinal excitability on the affected side compared to unaffected side. Further, results suggest that this asymmetry in corticospinal excitability is associated with duration of pain (n=39; r=0.45; p=0.005), but not with pain intensity (n=39; r<0.03; p>0.43). In contrast with findings in other populations with musculoskeletal pain, no significant inter-hemispheric asymmetry was observed in map location (n=16; p-values ⩾ 0.91), or in the amplitude of motor responses obtained at various stimulation intensities (n=16; p=0.83).

CONCLUSION

Chronicity of pain, but not its intensity, appears to be a factor related to lower excitability of infraspinatus representation.

SIGNIFICANCE

These results support the view that while cortical reorganization correlates with magnitude of pain in neuropathic pain syndromes, it could be more related to chronicity in the case of musculoskeletal disorders.

Evidence-based guidelines on the therapeutic use of repetitive transcranial magnetic stimulation (rTMS)

A group of European experts was commissioned to establish guidelines on the therapeutic use of repetitive transcranial magnetic stimulation (rTMS) from evidence published up until March 2014, regarding pain, movement disorders, stroke, amyotrophic lateral sclerosis, multiple sclerosis, epilepsy, consciousness disorders, tinnitus, depression, anxiety disorders, obsessive-compulsive disorder, schizophrenia, craving/addiction, and conversion. Despite unavoidable inhomogeneities, there is a sufficient body of evidence to accept with level A (definite efficacy) the analgesic effect of high-frequency (HF) rTMS of the primary motor cortex (M1) contralateral to the pain and the antidepressant effect of HF-rTMS of the left dorsolateral prefrontal cortex (DLPFC). A Level B recommendation (probable efficacy) is proposed for the antidepressant effect of low-frequency (LF) rTMS of the right DLPFC, HF-rTMS of the left DLPFC for the negative symptoms of schizophrenia, and LF-rTMS of contralesional M1 in chronic motor stroke. The effects of rTMS in a number of indications reach level C (possible efficacy), including LF-rTMS of the left temporoparietal cortex in tinnitus and auditory hallucinations. It remains to determine how to optimize rTMS protocols and techniques to give them relevance in routine clinical practice. In addition, professionals carrying out rTMS protocols should undergo rigorous training to ensure the quality of the technical realization, guarantee the proper care of patients, and maximize the chances of success. Under these conditions, the therapeutic use of rTMS should be able to develop in the coming years.

Chronic pain following physical and emotional trauma: the station nightclub fire

OBJECTIVE

The purpose of this study was to evaluate factors associated with chronic pain in survivors of a large fire, including those with and without burn injury.

METHODS

This study employed a survey-based cross-sectional design to evaluate data from survivors of The Station nightclub fire. The primary outcome measure was the presence and severity of pain. Multiple linear regressions with a stepwise approach were used to examine relationships among variables. Variables considered included age, gender, marital status, burn injury, total body surface area, skin graft, pre-morbid employment, time off work, return to same employment, depression (Beck depression inventory, BDI), and post-traumatic stress (impact of event scale - revised).

RESULTS

Of 104 fire survivors, 27% reported pain at least 28 months after the event. Multiple factors associated with pain were assessed in the univariate analysis but only age (p = 0.012), graft (p = 0.009), and BDI score (p < 0.001) were significantly associated with pain in the multiple regression model.

DISCUSSION

A significant number of fire survivors with and without burn injuries experienced chronic pain. Depth of burn and depression were significantly associated with pain outcome. Pain management should address both physical and emotional risk factors in this population.

Repetitive transcranial magnetic stimulation increases the corticospinal inhibition and the brain-derived neurotrophic factor in chronic myofascial pain syndrome: an explanatory double-blinded, randomized, sham-controlled trial

Chronic myofascial pain syndrome has been related to defective descending inhibitory systems. Twenty-four females aged 19 to 65 years with chronic myofascial pain syndrome were randomized to receive 10 sessions of repetitive transcranial magnetic stimulation (rTMS) (n = 12) at 10 Hz or a sham intervention (n = 12). We tested if pain (quantitative sensory testing), descending inhibitory systems (conditioned pain modulation [quantitative sensory testing + conditioned pain modulation]), cortical excitability (TMS parameters), and the brain-derived neurotrophic factor (BDNF) would be modified. There was a significant interaction (time vs group) regarding the main outcomes of the pain scores as indexed by the visual analog scale on pain (analysis of variance, P < .01). Post hoc analysis showed that compared with placebo-sham, the treatment reduced daily pain scores by -30.21% (95% confidence interval = -39.23 to -21.20) and analgesic use by -44.56 (-57.46 to -31.67). Compared to sham, rTMS enhanced the corticospinal inhibitory system (41.74% reduction in quantitative sensory testing + conditioned pain modulation, P < .05), reduced the intracortical facilitation in 23.94% (P = .03), increased the motor evoked potential in 52.02% (P = .02), and presented 12.38 ng/mL higher serum BDNF (95% confidence interval = 2.32-22.38). No adverse events were observed. rTMS analgesic effects in chronic myofascial pain syndrome were mediated by top-down regulation mechanisms, enhancing the corticospinal inhibitory system possibly via BDNF secretion modulation.

PERSPECTIVE

High-frequency rTMS analgesic effects were mediated by top-down regulation mechanisms enhancing the corticospinal inhibitory, and this effect involved an increase in BDNF secretion.

Nerve injury-induced neuropathic pain causes disinhibition of the anterior cingulate cortex

Neuropathic pain caused by peripheral nerve injury is a debilitating neurological condition of high clinical relevance. On the cellular level, the elevated pain sensitivity is induced by plasticity of neuronal function along the pain pathway. Changes in cortical areas involved in pain processing contribute to the development of neuropathic pain. Yet, it remains elusive which plasticity mechanisms occur in cortical circuits. We investigated the properties of neural networks in the anterior cingulate cortex (ACC), a brain region mediating affective responses to noxious stimuli. We performed multiple whole-cell recordings from neurons in layer 5 (L5) of the ACC of adult mice after chronic constriction injury of the sciatic nerve of the left hindpaw and observed a striking loss of connections between excitatory and inhibitory neurons in both directions. In contrast, no significant changes in synaptic efficacy in the remaining connected pairs were found. These changes were reflected on the network level by a decrease in the mEPSC and mIPSC frequency. Additionally, nerve injury resulted in a potentiation of the intrinsic excitability of pyramidal neurons, whereas the cellular properties of interneurons were unchanged. Our set of experimental parameters allowed constructing a neuronal network model of L5 in the ACC, revealing that the modification of inhibitory connectivity had the most profound effect on increased network activity. Thus, our combined experimental and modeling approach suggests that cortical disinhibition is a fundamental pathological modification associated with peripheral nerve damage. These changes at the cortical network level might therefore contribute to the neuropathic pain condition.

Brain stimulation in migraine

Migraine is a very prevalent disease with great individual disability and socioeconomic burden. Despite intensive research effort in recent years, the etiopathogenesis of the disease remains to be elucidated. Recently, much importance has been given to mechanisms underlying the cortical excitability that has been suggested to be dysfunctional in migraine. In recent years, noninvasive brain stimulation techniques based on magnetic fields (transcranial magnetic stimulation, TMS) and on direct electrical currents (transcranial direct current stimulation, tDCS) have been shown to be safe and effective tools to explore the issue of cortical excitability, activation, and plasticity in migraine. Moreover, TMS, repetitive TMS (rTMS), and tDCS, thanks to their ability to interfere with and/or modulate cortical activity inducing plastic, persistent effects, have been also explored as potential therapeutic approaches, opening an interesting perspective for noninvasive neurostimulation for both symptomatic and preventive treatment of migraine and other types of headache. In this chapter we critically review evidence regarding the role of noninvasive brain stimulation in the pathophysiology and treatment of migraine, delineating the advantages and limits of these techniques together with potential development and future application.

Non-invasive brain stimulation techniques for chronic pain

BACKGROUND

This is an updated version of the original Cochrane review published in 2010, Issue 9. Non-invasive brain stimulation techniques aim to induce an electrical stimulation of the brain in an attempt to reduce chronic pain by directly altering brain activity. They include repetitive transcranial magnetic stimulation (rTMS), cranial electrotherapy stimulation (CES), transcranial direct current stimulation (tDCS) and reduced impedance non-invasive cortical electrostimulation (RINCE).

OBJECTIVES

To evaluate the efficacy of non-invasive brain stimulation techniques in chronic pain.

SEARCH METHODS

We searched CENTRAL (2013, Issue 6), MEDLINE, EMBASE, CINAHL, PsycINFO, LILACS and clinical trials registers. The original search for the review was run in November 2009 and searched all databases from their inception. To identify studies for inclusion in this update we searched from 2009 to July 2013.

SELECTION CRITERIA

Randomised and quasi-randomised studies of rTMS, CES, tDCS or RINCE if they employed a sham stimulation control group, recruited patients over the age of 18 with pain of three months duration or more and measured pain as a primary outcome.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted and verified data. Where possible we entered data into meta-analyses. We excluded studies judged as being at high risk of bias from the analysis. We used the GRADE system to summarise the quality of evidence for core comparisons.

MAIN RESULTS

We included an additional 23 trials (involving 773 participants randomised) in this update, making a total of 56 trials in the review (involving 1710 participants randomised). This update included a total of 30 rTMS studies, 11 CES, 14 tDCS and one study of RINCE(the original review included 19 rTMS, eight CES and six tDCS studies). We judged only three studies as being at low risk of bias across all criteria.Meta-analysis of studies of rTMS (involving 528 participants) demonstrated significant heterogeneity. Pre-specified subgroup analyses suggest that low-frequency stimulation is ineffective (low-quality evidence) and that rTMS applied to the dorsolateral prefrontal cortex is ineffective (very low-quality evidence). We found a short-term effect on pain of active high-frequency stimulation of the motor cortex in single-dose studies (low-quality evidence, standardised mean difference (SMD) 0.39 (95% confidence interval (CI) -0.27 to -0.51 P < 0.01)). This equates to a 12% (95% CI 8% to 15%) reduction in pain, which does not exceed the pre-established criteria for a minimal clinically important difference (≥ 15%). Evidence for multiple-dose studies was heterogenous but did not demonstrate a significant effect (very low-quality evidence).For CES (six studies, 270 participants) no statistically significant difference was found between active stimulation and sham (low-quality evidence).Analysis of tDCS studies (11 studies, 193 people) demonstrated significant heterogeneity and did not find a significant difference between active and sham stimulation (very low-quality evidence). Pre-specified subgroup analysis of tDCS applied to the motor cortex (n = 183) did not demonstrate a statistically significant effect and this lack of effect was consistent for subgroups of single or multiple-dose studies.One small study (n = 91) at unclear risk of bias suggested a positive effect of RINCE over sham stimulation on pain (very low-quality evidence).Non-invasive brain stimulation appears to be frequently associated with minor and transient side effects, though there were two reported incidences of seizure related to active rTMS in the included studies.

AUTHORS' CONCLUSIONS

Single doses of high-frequency rTMS of the motor cortex may have small short-term effects on chronic pain. It is likely that multiple sources of bias may exaggerate this observed effect. The effects do not meet the predetermined threshold of minimal clinical significance and multiple-dose studies do not consistently demonstrate effectiveness. The available evidence suggests that low-frequency rTMS, rTMS applied to the pre-frontal cortex, CES and tDCS are not effective in the treatment of chronic pain. While the broad conclusions for rTMS and CES have not changed substantially, the addition of this new evidence and the application of the GRADE system has modified some of our interpretation and the conclusion regarding the effectiveness of tDCS has changed. We recommend that previous readers should re-read this update. There is a need for larger, rigorously designed studies, particularly of longer courses of stimulation. It is likely that future evidence may substantially impact upon the presented results.

Pressure pain thresholds increase after preconditioning 1 Hz repetitive transcranial magnetic stimulation with transcranial direct current stimulation

BACKGROUND

The primary motor cortex (M1) is an effective target of non-invasive cortical stimulation (NICS) for pain threshold modulation. It has been suggested that the initial level of cortical excitability of M1 plays a key role in the plastic effects of NICS.

OBJECTIVE

Here we investigate whether transcranial direct current stimulation (tDCS) primed 1 Hz repetitive transcranial magnetic stimulation (rTMS) modulates experimental pressure pain thresholds and if this is related to observed alterations in cortical excitability.

METHOD

15 healthy, male participants received 10 min 1 mA anodal, cathodal and sham tDCS to the left M1 before 15 min 1 Hz rTMS in separate sessions over a period of 3 weeks. Motor cortical excitability was recorded at baseline, post-tDCS priming and post-rTMS through recording motor evoked potentials (MEPs) from right FDI muscle. Pressure pain thresholds were determined by quantitative sensory testing (QST) through a computerized algometer, on the palmar thenar of the right hand pre- and post-stimulation.

RESULTS

Cathodal tDCS-primed 1 Hz-rTMS was found to reverse the expected suppressive effect of 1 Hz rTMS on cortical excitability; leading to an overall increase in activity (p<0.001) with a parallel increase in pressure pain thresholds (p<0.01). In contrast, anodal tDCS-primed 1 Hz-rTMS resulted in a corresponding decrease in cortical excitability (p<0.05), with no significant effect on pressure pain.

CONCLUSION

This study demonstrates that priming the M1 before stimulation of 1 Hz-rTMS modulates experimental pressure pain thresholds in a safe and controlled manner, producing a form of analgesia.

Modulation of intracortical inhibition in response to acute psychosocial stress is impaired among individuals with chronic neck pain

OBJECTIVE

Psychosocial stress has been associated with a variety of chronic pain disorders although the mechanisms responsible for this relationship are unknown. The purpose of this study was to compare the excitability of intracortical and corticospinal pathways to the trapezius muscle in individuals with and without chronic neck pain during exposure to low and high levels of psychosocial stress.

METHODS

Single and paired-pulse transcranial magnetic stimulation was used to assess motor evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) during mental math performed in the presence and absence of social evaluative threat.

RESULTS

All participants demonstrated higher amplitude MEPs in the high stress compared to the low stress condition (p < 0.01). Participants with chronic neck pain had significantly greater SICI than healthy participants in the low stress condition (p = 0.03). During exposure to the stressor, healthy participants showed an increase in SICI, whereas participants with neck pain showed no change (group difference for change in SICI, p < 0.01).

CONCLUSIONS

These findings suggest that individuals with chronic neck pain inhibit motor output to the trapezius in the presence of minor stressors, and are unable to compensate for additional stress-evoked increases in corticospinal excitability through further modulation of SICI. This observation has potential implications for the management of patients who have difficulty relaxing painful muscles during times of stress.