Noninvasive neuromodulation techniques for the management of phantom limb pain: a systematic review of randomized controlled trials

Beyond traditional therapies: a network meta-analysis on the treatment efficacy for chronic phantom limb pain

BACKGROUND

Phantom limb pain (PLP) frequently affects individuals with limb amputations. When PLP evolves into its chronic phase, known as chronic PLP, traditional therapies often fall short in providing sufficient relief. The optimal intervention for chronic PLP remains unclear.

OBJECTIVE

The objectives of this network meta-analysis (NMA) were to examine the efficacy of different treatments on pain intensity for patients with chronic PLP.

EVIDENCE REVIEW

We searched Medline, EMBASE, Cochrane CENTRAL, Scopus, and CINAHL EBSCO, focusing on randomized controlled trials (RCTs) that evaluated interventions such as neuromodulation, neural block, pharmacological methods, and alternative treatments. An NMA was conducted based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The primary outcome was pain score improvement, and the secondary outcomes were adverse events.

FINDINGS

The NMA, incorporating 12 RCTs, indicated that neuromodulation, specifically repetitive transcranial magnetic stimulation, provided the most substantial pain improvement when compared with placebo/sham groups (mean difference=-2.9 points, 95% CI=-4.62 to -1.18; quality of evidence (QoE): moderate). Pharmacological intervention using morphine was associated with a significant increase in adverse event rate (OR=6.04, 95% CI=2.26 to 16.12; QoE: low).

CONCLUSIONS

The NMA suggests that neuromodulation using repetitive transcranial magnetic stimulation may be associated with significantly larger pain improvement for chronic PLP. However, the paucity of studies, varying patient characteristics across each trial, and absence of long-term results underscore the necessity for more comprehensive, large-scale RCTs.

PROSPERO REGISTRATION NUMBER

CRD42023455949.

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.

Evolving techniques for reducing phantom limb pain

At least two million people in the United States of America live with lost limbs, and the number is expected to double by 2050, although the incidence of amputations is significantly greater in other parts of the world. Within days to weeks of the amputation, up to 90% of these individuals develop neuropathic pain, presenting as phantom limb pain (PLP). The pain level increases significantly within one year and remains chronic and severe for about 10%. Amputation-induced changes are considered to underlie the causation of PLP. Techniques applied to the central nervous system (CNS) and peripheral nervous system (PNS) are designed to reverse amputation-induced changes, thereby reducing/eliminating PLP. The primary treatment for PLP is the administration of pharmacological agents, some of which are considered but provide no more than short-term pain relief. Alternative techniques are also discussed, which provide only short-term pain relief. Changes induced by various cells and the factors they release are required to change neurons and their environment to reduce/eliminate PLP. It is concluded that novel techniques that utilize autologous platelet-rich plasma (PRP) may provide long-term PLP reduction/elimination.

Transcranial direct current stimulation in the management of phantom limb pain: a systematic review of randomized controlled trials

INTRODUCTION

Phantom limb pain (PLP) after amputation is a frequent entity that conditions the life of those who suffer it. Current treatment methods are not sufficiently effective for PLP management. We aim to analyze the clinical application of transcranial direct current (tDCS) in people with amputation suffering from PLP.

EVIDENCE ACQUISITION

The following databases were consulted in September 2021: MEDLINE, EMBASE, The Web of Science, PEDro, SCOPUS and SciELO. Randomized controlled trials investigating the use of tDCS in people with amputation undergoing PLP were selected. Demographic data, type and cause of amputation, time since amputation, stimulation parameters, and outcomes were extracted.

EVIDENCE SYNTHESIS

Six articles were included in this review (seven studies were considered because one study performed two individual protocols). All included studies evaluated PLP; six evaluated the phantom limb sensations (PLS) and two evaluated the psychiatric disorders. In all included studies the intensity and frequency of PLP was reduced, in three PLS were reduced, and in none study psychiatric symptoms were modified.

CONCLUSIONS

Anodic tDCS over the contralateral M1 to the affected limb, with an intensity of 1-2 mA, for 15-20 minutes seems to significantly reduce PLP in people with amputation. Single-session treatment could modify PLP intensity for hours, and multi-session treatment could modify PLP for months. Limited evidence suggests that PLS and psychiatric disorders should be treated with different PLP electrode placements. Further studies with larger sample size and longer follow-up times are needed to establish the priority of tDCS application in the PLP management.

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.

Neuromodulation Techniques in Phantom Limb Pain: A Systematic Review and Meta-analysis

OBJECTIVE

To evaluate the effects of neuromodulation techniques in adults with phantom limb pain (PLP).

METHODS

A systematic search was performed, comprising randomized controlled trials (RCTs) and quasi-experimental (QE) studies that were published from database inception to February 2019 and that measured the effects of neuromodulation in adults with PLP. Hedge's g effect size (ES) and 95% confidence intervals were calculated, and random-effects meta-analyses were performed.

RESULTS

Fourteen studies (nine RCTs and five QE noncontrolled studies) were included. The meta-analysis of RCTs showed significant effects for i) excitatory primary motor cortex (M1) stimulation in reducing pain after stimulation (ES = -1.36, 95% confidence interval [CI] = -2.26 to -0.45); ii) anodal M1 transcranial direct current stimulation (tDCS) in lowering pain after stimulation (ES = -1.50, 95% CI = -2.05 to 0.95), and one-week follow-up (ES = -1.04, 95% CI = -1.64 to 0.45). The meta-analysis of noncontrolled QE studies demonstrated a high rate of pain reduction after stimulation with transcutaneous electrical nerve stimulation (rate = 67%, 95% CI = 60% to 73%) and at one-year follow-up with deep brain stimulation (rate = 73%, 95% CI = 63% to 82%).

CONCLUSIONS

The evidence from RCTs suggests that excitatory M1 stimulation-specifically, anodal M1 tDCS-has a significant short-term effect in reducing pain scale scores in PLP. Various neuromodulation techniques appear to have a significant and positive impact on PLP, but due to the limited amount of data, it is not possible to draw more definite conclusions.