Transcranial Direct Current Stimulation for the Reduction of Clinical and Experimentally Induced Pain: A Systematic Review and Meta-analysis

Analgesic efficacy of cerebral and peripheral electrical stimulation in chronic nonspecific low back pain: a randomized, double-blind, factorial clinical trial

BACKGROUND

Chronic non-specific low back pain is a major socioeconomic public health issue worldwide and, despite the volume of research in the area, it is still a difficult-to-treat condition. The conservative analgesic therapy usually comprises a variety of pharmacological and non-pharmacological strategies, such as transcutaneous electrical nerve stimulation. The neuromatrix pain model and the new findings on the process of chronicity of pain point to a higher effectiveness of treatments that address central rather than peripheral structures. The transcranial direct current stimulation is a noninvasive technique of neuromodulation that has made recent advances in the treatment of chronic pain. The simultaneous combination of these two electrostimulation techniques (cerebral and peripheral) can provide an analgesic effect superior to isolated interventions. However, all the evidence on the analgesic efficacy of these techniques, alone or combined, is still fragmented. This is a protocol for a randomized clinical trial to investigate whether cerebral electrical stimulation combined with peripheral electrical stimulation is more effective in relieving pain than the isolated application of electrical stimulations in patients with chronic nonspecific low back pain.

METHODS/DESIGN

Ninety-two patients will be randomized into four groups to receive transcranial direct current stimulation (real/sham) + transcutaneous electrical nerve stimulation (real/sham) for 12 sessions over a period of four weeks. The primary clinical outcome (pain intensity) and the secondary ones (sensory and affective aspects of pain, physical functioning and global perceived effect) will be recorded before treatment, after four weeks, in Month 3 and in Month 6 after randomization. Confounding factors such as anxiety and depression, the patient's satisfaction with treatment and adverse effects will also be listed. Data will be collected by an examiner unaware of (blind to) the treatment allocation.

DISCUSSION

The results of this study may assist in clinical decision-making about the combined use of cerebral and peripheral electrical stimulation for pain relief in patients with chronic low back pain.

TRIAL REGISTRATION

NCT01896453.

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.

Pearls and pitfalls: neurostimulation in headache

CONTEXT

A variety of neuromodulatory approaches available today has broadened our therapeutic options significantly especially in drug refractory patients with chronic cluster headache and chronic migraine.

OVERVIEW

It is a dynamic field with a current trend to non-invasive transcutaneous stimulation approaches. However, sound studies providing evidence for the widespread use of these novel approaches are sparse. For invasive approaches, occipital nerve stimulation is now widely considered the treatment of first choice in chronic trigeminal autonomic cephalgias and - with limitations - chronic migraine. Although equally effective, deep brain stimulation is considered second-line treatment in cluster headache because of its potentially life-threatening side effects. Most recently, stimulation of the sphenopalatine ganglion has also been shown to effectively abort acute cluster headache attacks. Interesting other upcoming approaches include transcutaneous supraorbital nerve stimulation and transcutaneous vagal nerve stimulation.

CONCLUSION

Pearls and pitfalls of common invasive and non-invasive neuromodulatory approaches and open questions are summarised in this review along with recommendations for future studies.

Transcranial Direct Current Stimulation in Neuropathic Pain

Neuropathic pain (NP) is one of the most common problems contributing to suffering and disability worldwide. Unfortunately, NP is also largely refractory to treatments, with a large number of patients continuing to report significant pain even when they are receiving recommended medications and physical therapy. Thus, there remains an urgent need for additional effective treatments. In recent years, nonpharmacologic brain stimulation techniques have emerged as potential therapeutic options. Many of these techniques and procedures – such as transcranial magnetic stimulation, spinal cord stimulation, deep brain stimulation, and motor cortical stimulation – have very limited availability, particularly in developing countries. Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation procedure that has shown promise for effectively treating NP, and also has the potential to be widely available. This review describes tDCS and the tDCS procedures and principles that may be helpful for treating NP. The findings indicate that the analgesic benefits of tDCS can occur both during stimulation and beyond the time of stimulation. The mechanisms of cortical modulation by tDCS may involve various activities in neuronal networks such as increasing glutamine and glutamate under the stimulating electrode, effects on the μ-opioid receptor, and restoration of the defective intracortical inhibition. Additional research is needed to determine (1) the factors that may moderate the efficacy of tDCS, (2) the dose (e.g. number and frequency of treatment sessions) that results in the largest benefits and (3) the long-term effects of tDCS treatment.

Motor cortex stimulation activates the incertothalamic pathway in an animal model of spinal cord injury

We have shown previously that electrical stimulation of the motor cortex reduces spontaneous painlike behaviors in animals with spinal cord injury (SCI). Because SCI pain behaviors are associated with abnormal inhibition in the inhibitory nucleus zona incerta (ZI) and because inactivation of the ZI blocks motor cortex stimulation (MCS) effects, we hypothesized that the antinociceptive effects of MCS are due to enhanced inhibitory inputs from ZI to the posterior thalamus (Po)-an area heavily implicated in nociceptive processing. To test this hypothesis, we used a rodent model of SCI pain and performed in vivo extracellular electrophysiological recordings in single well-isolated neurons in anesthetized rats. We recorded spontaneous activity in ZI and Po from 48 rats before, during, and after MCS (50 μA, 50 Hz; 300-ms pulses). We found that MCS enhanced spontaneous activity in 35% of ZI neurons and suppressed spontaneous activity in 58% of Po neurons. The majority of MCS-enhanced ZI neurons (81%) were located in the ventrorateral subdivision of ZI-the area containing Po-projecting ZI neurons. In addition, we found that inactivation of ZI using muscimol (GABAA receptor agonist) blocked the effects of MCS in 73% of Po neurons. Although we cannot eliminate the possibility that muscimol spread to areas adjacent to ZI, these findings support our hypothesis and suggest that MCS produces antinociception by activating the incertothalamic pathway.

PERSPECTIVE

This article describes a novel brain circuit that can be manipulated, in rats, to produce antinociception. These results have the potential to significantly impact the standard of care currently in place for the treatment of patients with intractable pain.