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

Effects of multiple transcranial magnetic stimulation sessions on pain relief in patients with chronic neuropathic pain: A French cohort study in real-world clinical practice

BACKGROUND

Current clinical trials indicate that repetitive transcranial magnetic stimulation (rTMS) is effective in reducing drug-resistant neuropathic pain (NP). However, there is a lack of studies evaluating the long-term feasibility and clinical efficacy of rTMS in large patient cohorts in real-world conditions.

METHODS

In this retrospective cohort study, we analysed 12 years of clinical data to assess the long-term analgesic effects of 20 Hz rTMS over the primary motor cortex in patients with NP. Subgroup analyses were conducted to identify predictive factors and assess the potential role of epidural motor cortex stimulation (eMCS) as a sustained solution.

RESULTS

In total, 193 patients completed test period of 4 rTMS sessions and 42% of them reported a pain relief (PR) greater than 30%, with concurrent improvement in their most disabling symptom. Iterative rTMS sessions maintained analgesic effects over 10 years in certain patients identified as responders (≥10% PR) without adverse effects. Success probability was higher in patients with central NP compared to peripheral NP (OR = 2.03[1.04;4.00]), and among those with central post-stroke pain, this probability was higher in ischemic versus hemorrhagic strokes (OR = 3.36[1.17;10.05]). PR obtained with iterative rTMS sessions was an excellent predictor of eMCS efficacy.

CONCLUSIONS

While rTMS shows promise as a therapeutic option for some patients with drug-resistant NP, it does not benefit all patients. Efficacy varies by NP aetiology, aiding patient selection. For responders, eMCS may offer a permanent solution. These findings support a tailored approach to rTMS in NP management, while recognizing both its potential and limitations across diverse patient profiles.

SIGNIFICANCE STATEMENT

Multiple rTMS sessions demonstrate long-term efficacy and safety in treating drug-resistant neuropathic pain. Extending session numbers for the test period can enhance responder identification, especially in patients with initial low pain relief. This identification refines patient selection for neurosurgery, reducing non-responders. Central neuropathic pain shows higher success rates than peripheral. For post-stroke central pain, patients with ischemic stroke are more likely to respond than those with hemorrhagic stroke. These results support integrating rTMS into clinical practice for managing neuropathic pain.

Prediction of the response to repetitive transcranial magnetic stimulation of the motor cortex in peripheral neuropathic pain and validation of a new algorithm

CLINICAL TRIAL REGISTRATION

NCT02010281.

Posterior-superior insula repetitive transcranial magnetic stimulation reduces experimental tonic pain and pain-related cortical inhibition in humans

ABSTRACT

High frequency repetitive transcranial magnetic stimulation (rTMS) to the posterior-superior insula (PSI) may produce analgesic effects. However, the alterations in cortical activity during PSI-rTMS analgesia remain poorly understood. The present study aimed to determine whether tonic capsaicin-induced pain and cortical inhibition (indexed using TMS-electroencephalography) are modulated by PSI-rTMS. Twenty healthy volunteers (10 females) attended 2 sessions randomized to active or sham rTMS. Experimental pain was induced by capsaicin administered to the forearm for 90 minutes, with pain ratings collected every 5 minutes. Left PSI-rTMS was delivered (10 Hz, 100 pulses per train, 15 trains) ∼50 minutes postcapsaicin administration. Transcranial magnetic stimulation-evoked potentials (TEPs) and thermal sensitivity were assessed at baseline, during capsaicin pain prior to rTMS and after rTMS. Bayesian evidence of reduced pain scores and increased heat pain thresholds were found after active rTMS, with no changes occurring after sham rTMS. Pain (prior to active rTMS) led to an increase in the frontal negative peak ∼45 ms (N45) TEP relative to baseline. After active rTMS, there was a decrease in the N45 peak back to baseline levels. In contrast, after sham rTMS, the N45 peak was increased relative to baseline. We also found that the reduction in pain numerical rating scale scores after active vs sham rTMS was correlated with and partially mediated by decreases in the N45 peak. These findings provide evidence of the analgesic effects of PSI-rTMS and suggest that the TEP N45 peak is a potential marker and mediator of both pain and analgesia. This study demonstrates that high-frequency rTMS targeting the posterior-superior insula reduces capsaicin-induced pain and alters cortical activity, with changes in the N45 TMS-evoked potential peak mediating the analgesic effects.

H-Coil Repetitive Transcranial Magnetic Stimulation Relieves Pain and Symptoms of Anxiety and Depression in Patients With Chronic Peripheral Neuropathic Pain: A Randomized Sham-Controlled Crossover Study

OBJECTIVES

This study aimed to investigate the analgesic effects of H-coil repetitive transcranial magnetic stimulation (rTMS) primarily targeting the hand area of the primary motor cortex (M1) in patients with peripheral neuropathic pain. Given that the H-coil has a wider reach than conventional coils, there is a possibility that targeting the hand motor cortex also may stimulate prefrontal areas. Thus, we also aimed to examine whether rTMS with an M1 target could produce effects on psychologic outcomes.

MATERIALS AND METHODS

In total, 17 patients were randomly assigned to receive active or sham H-coil rTMS in a counterbalanced order. After a nine-week washout period, they crossed over to either active or sham rTMS, according to a double-blind crossover design. Each treatment period consisted of five daily rTMS sessions and a one- and three-week follow-up visit. The primary outcome was average usual pain intensity. Secondary outcomes included pain unpleasantness, dynamic and static mechanical allodynia, anxiety and depression, sleep, pain catastrophizing, function, and patients' impression of change. Effects of rTMS were investigated using linear mixed model analyses.

RESULTS

We found two significant interactions between treatment and time, indicating that active H-coil rTMS induced significant analgesic effects (t [134] = -2.18; p = .03; d = -0.10) and significant reductions in anxiety and depression compared with sham stimulation over the treatment course (t [73] = -2.14; p = .04; d = -0.09). The analgesic effect occurred two weeks after the treatment, and the effect on anxiety and depression occurred three weeks after treatment. No other significant interactions were found for the secondary variables.

CONCLUSIONS

Five days of H-coil rTMS targeting the hand area of M1 induced statistically significant effects on pain intensity. Moreover, rTMS improved symptoms of anxiety and depression, possibly because of the wide and deep reach of the H-coil.

CLINICAL TRIAL REGISTRATION

The Clinicaltrials.gov registration number for the study is NCT05488808.

Neuromodulation for neuropathic pain

The treatment of neuropathic pain (NeP) often leads to partial or incomplete pain relief, with up to 40 % of patients being pharmaco-resistant. In this chapter the efficacy of neuromodulation techniques in treating NeP is reviewed. It presents a detailed evaluation of the mechanisms of action and evidence supporting the clinical use of the most common approaches like transcutaneous electrical nerve stimulation (TENS), transcranial direct current stimulation (tDCS), repetitive transcranial magnetic stimulation (rTMS), deep brain stimulation (DBS), invasive motor cortex stimulation (iMCS), spinal cord stimulation (SCS), dorsal root ganglion stimulation (DRG-S), and peripheral nerve stimulation (PNS). Current literature suggests that motor cortex rTMS is effective for peripheral and central NeP, and TENS for peripheral NeP. Evidence for tDCS is inconclusive. DBS is reserved for research settings due to heterogeneous results, while iMSC has shown efficacy in a small randomized trial in neuropathic pain due to stroke and brachial plexus avulsion. SCS has moderate evidence for painful diabetic neuropathy and failed back surgery syndrome, but trials were not controlled with sham. DRG-S and PNS have shown positive results for complex regional pain syndrome and post-surgical neuropathic pain, respectively. Adverse effects vary, with non-invasive techniques showing local discomfort, dizziness and headache, and DBS and SCS hardware-related issues. To date, non-invasive techniques have been more extensively studied and some are included in international guidelines, while the evidence level for invasive techniques are less robust, potentially suggesting their use in a case-by-case indication considering patient´s preferences, costs and expected benefits.

10-Day Theta Burst Stimulation Intervention Facilitates the Clinical Rehabilitation of Patients After an Isolated Limb Fracture: A Longitudinal SHAM-Controlled Pilot Study

OBJECTIVE

We investigated if theta burst stimulation could enhance recovery by reducing key symptoms when implemented acutely postfracture in participants with an isolated upper limb fracture.

METHODS/DESIGN

This was a pilot study with a randomized matched pair, sham-controlled, participant-blind design of a 10-day prolonged continuous theta burst stimulation protocol. Two main groups were included: I) participants with isolated upper limb fracture receiving active theta burst stimulation and II) patients with isolated upper limb fracture receiving SHAM/placebo. Another group (III) of healthy individuals was the reference group. Disability and pain intensity were collected through questionnaires (disabilities of the Arm, Shoulder, and Hand as well as numerical rating scale (NRA)) at three time points (baseline; 72 hrs after intervention, 3 mos after injury). Group III completed the baseline assessment.

RESULTS

Seventy-nine participants were enrolled. Individuals in the ACTIVE and SHAM groups had similar baseline measures. For disability, the interaction between intervention and time approached significance (F = 2.33; P = 0.11), whereas it was significant for pain (F = 3.42; P = 0.04). At 3 mos after injury, the ACTIVE group reported reduced disability (F = 4.71; P = 0.04) and pain (F = 5.84; P = 0.02) at 3 mos after injury compared to the SHAM group, with clinical measures from ACTIVE group being like controls.

CONCLUSIONS

In isolated upper limb fracture patients, a 10-day theta burst stimulation intervention implemented acutely posttrauma had beneficial effects on symptoms of functional recovery and pain at 3 mos after trauma.

Management of Central Post-Stroke Pain: Systematic Review and Meta-Analysis

Central post stroke pain (CPSP) is a neuropathic pain condition prevalent in 8% to 35% of stroke patients. This systematic review and meta-analysis aimed to provide insight in the effectiveness of available pharmacological, physical, psychological, and neuromodulation intervention in reducing pain in CPSP patients (PROSPERO Registration: CRD42022371835). Secondary outcomes included mood, sleep, global impression of change, and physical responses. Data extraction included participant demographics, stroke aetiology, pain characteristics, pain reduction scores, and secondary outcome metrics. Forty two original studies were included with a total of 1451 participants. No studies providing psychological therapy to CPSP patients were identified. Twelve studies met requirements for a random-effects meta-analyses that found: pharmacological therapy to have a small effect on mean pain score (SMD = -0.36, 96.0% Confidence Interval [-0.68, -0.03], physical interventions did not show a significant effect (SMD = -0.55, [-1.28, 0.18]), and neuromodulation treatments had a moderate effect (SMD -0.64, [-1.08, -0.19]). Fourteen studies were included in proportional meta-analysis with pharmacological studies having a moderate effect (58.3% mean pain reduction, [-36.51, -80.15]), and neuromodulation studies a small effect (31.1% mean pain reduction, [-43.45, -18.76]). Sixteen studies were included in the narrative review, findings from which largely supported meta-analyses results. Duloxetine, Amitriptyline and repetitive Transcranial Magnetic Stimulation (rTMS) had the most robust evidence for their effectiveness in alleviating CPSP induced pain. Further multi-centre placebo-controlled research is needed to ascertain the effectiveness of physical therapies, such as acupuncture and virtual reality, and invasive and non-invasive neuromodulation treatments. PERSPECTIVE: This article presents a top-down and bottom-up overview of evidence for the effectiveness of different pharmacological, physical, and neuromodulation treatments of CPSP. This review could provide clinicians with a comprehensive understanding of the effectiveness and tolerability of different treatment types.

Posterior insula repetitive transcranial magnetic stimulation for chronic pain in patients with Parkinson disease - pain type matters: A double-blinded randomized sham-controlled trial

OBJECTIVES

Altered somatosensory processing in the posterior insula may play a role in chronic pain development and contribute to Parkinson disease (PD)-related pain. Posterior-superior insula (PSI) repetitive transcranial magnetic stimulation (rTMS) has been demonstrated to have analgesic effects among patients with some chronic pain conditions. This study aimed at assessing the efficacy of PSI-rTMS for treating PD-related pain.

METHODS

This was a double-blinded, randomized, sham-controlled, parallel-arm trial (NCT03504748). People with PD (PwP)-related chronic pain underwent five daily PSI-rTMS sessions for a week, followed by once weekly maintenance stimulations for seven weeks. rTMS was delivered at 10 Hz and 80% of the resting motor threshold. The primary outcome was a ≥ 30% pain intensity reduction at 8 weeks compared to baseline. Functionality, mood, cognitive, motor status, and somatosensory thresholds were also assessed.

RESULTS

Twenty-five patients were enrolled. Mean age was 55.2 ± 9.5 years-old, and 56% were female. Nociceptive pain accounted for 60%, and neuropathic and nociplastic for 20% each. No significant difference was found for 30% pain reduction response rates between active (42.7%) and sham groups (14.6%, p = 0.26). Secondary clinical outcomes and sensory thresholds also did not differ significantly. In a post hoc analysis, PwP with nociceptive pain sub-type experienced more pain relief after active (85.7%) compared to sham PSI-rTMS (25%, p = 0.032).

CONCLUSION

Our preliminary results suggest that different types of PD-related pain may respond differently to treatment, and therefore people with PD may benefit from having PD-related pain well characterized in research trials and in clinical practice.

The deep and the deeper: Spinal cord and deep brain stimulation for neuropathic pain

Neuropathic pain occurs in people experiencing lesion or disease affecting the somatosensorial system. It is present in 7 % of the general population and may not fully respond to first- and second-line treatments in up to 40 % of cases. Neuromodulation approaches are often proposed for those not tolerating or not responding to usual pharmacological management. These approaches can be delivered surgically (invasively) or non-invasively. Invasive neuromodulation techniques were the first to be employed in neuropathic pain. Among them is spinal cord stimulation (SCS), which consists of the implantation of epidural electrodes over the spinal cord. It is recommended in some guidelines for peripheral neuropathic pain. While recent studies have called into question its efficacy, others have provided promising data, driven by advances in techniques, battery capabilities, programming algorithms and software developments. Deep brain stimulation (DBS) is another well-stablished neuromodulation therapy routinely used for movement disorders; however, its role in pain management remains limited to specific research centers. This is not only due to variable results in the literature contesting its efficacy, but also because several different brain targets have been explored in small trials, compromising comparisons between these studies. Structures such as the periaqueductal grey, posterior thalamus, anterior cingulate cortex, ventral striatum/anterior limb of the internal capsule and the insula are the main targets described to date in literature. SCS and DBS present diverse rationales for use, mechanistic backgrounds, and varying levels of support from experimental studies. The present review aims to present their methodological details, main mechanisms of action for analgesia and their place in the current body of evidence in the management of patients with neuropathic pain, as well their particularities, effectiveness, safety and limitations.

Anatomo-physiological basis and applied techniques of electrical neuromodulation in chronic pain

Chronic pain, a complex and debilitating condition, poses a significant challenge to both patients and healthcare providers worldwide. Conventional pharmacological interventions often prove inadequate in delivering satisfactory relief while carrying the risks of addiction and adverse reactions. In recent years, electric neuromodulation emerged as a promising alternative in chronic pain management. This method entails the precise administration of electrical stimulation to specific nerves or regions within the central nervous system to regulate pain signals. Through mechanisms that include the alteration of neural activity and the release of endogenous pain-relieving substances, electric neuromodulation can effectively alleviate pain and improve patients' quality of life. Several modalities of electric neuromodulation, with a different grade of invasiveness, provide tailored strategies to tackle various forms and origins of chronic pain. Through an exploration of the anatomical and physiological pathways of chronic pain, encompassing neurotransmitter involvement, this narrative review offers insights into electrical therapies' mechanisms of action, clinical utility, and future perspectives in chronic pain management.

Evoked oscillatory cortical activity during acute pain: Probing brain in pain by transcranial magnetic stimulation combined with electroencephalogram

Temporal dynamics of local cortical rhythms during acute pain remain largely unknown. The current study used a novel approach based on transcranial magnetic stimulation combined with electroencephalogram (TMS-EEG) to investigate evoked-oscillatory cortical activity during acute pain. Motor (M1) and dorsolateral prefrontal cortex (DLPFC) were probed by TMS, respectively, to record oscillatory power (event-related spectral perturbation and relative spectral power) and phase synchronization (inter-trial coherence) by 63 EEG channels during experimentally induced acute heat pain in 24 healthy participants. TMS-EEG was recorded before, during, and after noxious heat (acute pain condition) and non-noxious warm (Control condition), delivered in a randomized sequence. The main frequency bands (α, β1, and β2) of TMS-evoked potentials after M1 and DLPFC stimulation were recorded close to the TMS coil and remotely. Cold and heat pain thresholds were measured before TMS-EEG. Over M1, acute pain decreased α-band oscillatory power locally and α-band phase synchronization remotely in parietal-occipital clusters compared with non-noxious warm (all p < .05). The remote (parietal-occipital) decrease in α-band phase synchronization during acute pain correlated with the cold (p = .001) and heat pain thresholds (p = .023) and to local (M1) α-band oscillatory power decrease (p = .024). Over DLPFC, acute pain only decreased β1-band power locally compared with non-noxious warm (p = .015). Thus, evoked-oscillatory cortical activity to M1 stimulation is reduced by acute pain in central and parietal-occipital regions and correlated with pain sensitivity, in contrast to DLPFC, which had only local effects. This finding expands the significance of α and β band oscillations and may have relevance for pain therapies.

Central neuropathic pain

Central neuropathic pain arises from a lesion or disease of the central somatosensory nervous system such as brain injury, spinal cord injury, stroke, multiple sclerosis or related neuroinflammatory conditions. The incidence of central neuropathic pain differs based on its underlying cause. Individuals with spinal cord injury are at the highest risk; however, central post-stroke pain is the most prevalent form of central neuropathic pain worldwide. The mechanisms that underlie central neuropathic pain are not fully understood, but the pathophysiology likely involves intricate interactions and maladaptive plasticity within spinal circuits and brain circuits associated with nociception and antinociception coupled with neuronal hyperexcitability. Modulation of neuronal activity, neuron-glia and neuro-immune interactions and targeting pain-related alterations in brain connectivity, represent potential therapeutic approaches. Current evidence-based pharmacological treatments include antidepressants and gabapentinoids as first-line options. Non-pharmacological pain management options include self-management strategies, exercise and neuromodulation. A comprehensive pain history and clinical examination form the foundation of central neuropathic pain classification, identification of potential risk factors and stratification of patients for clinical trials. Advanced neurophysiological and neuroimaging techniques hold promise to improve the understanding of mechanisms that underlie central neuropathic pain and as predictive biomarkers of treatment outcome.