Long-Term Results of Cortical Motor Stimulation for Neuropathic Peripheral and Central Pain: Real-World Evidence From Two Independent Centers

BACKGROUND AND OBJECTIVES

Cortical motor stimulation (CMS) is used to modulate neuropathic pain. The literature supports its use; however, short follow-up studies might overestimate its real effect. This study brings real-world evidence from two independent centers about CMS methodology and its long-term outcomes.

METHODS

Patients with chronic refractory neuropathic pain were implanted with CMS. The International Classification of Headache Disorders 3rd Edition was used to classify craniofacial pain and the Douleur Neuropathique en 4 Questions Scale score to explore its neuropathic nature. Demographics and clinical and surgical data were collected. Pain intensity at 6, 12, and 24 months and last follow-up was registered. Numeric rating scale reduction of ≥50% was considered a good response. The Clinical Global Impression of Change scale was used to report patient satisfaction.

RESULTS

Twelve males (38.7%) and 19 females (61.3%) with a mean age of 55.8 years (±11.9) were analyzed. Nineteen (61.5%) were diagnosed from painful trigeminal neuropathy (PTN), and seven (22.5%) from central poststroke pain. The mean follow-up was 51 months (±23). At 6 months, 42% (13/31) of the patients were responders, all of them being PTN (13/19; 68.4%). At last follow-up, only 35% (11/31) remained responders (11/19 PTN; 58%). At last follow-up, the global Numeric rating scale reduction was 34% ( P = .0001). The Clinical Global Impression of Change scale punctuated 2.39 (±0.94) after 3 months from the surgery and 2.95 (±1.32) at last follow-up ( P = .0079). Signs of suspicious placebo effect were appreciated in around 40% of the nonresponders.

CONCLUSION

CMS might show long-term efficacy for neuropathic pain syndromes, with the effect on PTN being more robust in the long term. Multicentric clinical trials are needed to confirm the efficacy of this therapy for this and other conditions.

Cortical stimulation for chronic pain: from anecdote to evidence

Epidural stimulation of the motor cortex (eMCS) was devised in the 1990's, and has now largely supplanted thalamic stimulation for neuropathic pain relief. Its mechanisms of action involve activation of multiple cortico-subcortical areas initiated in the thalamus, with involvement of endogenous opioids and descending inhibition toward the spinal cord. Evidence for clinical efficacy is now supported by at least seven RCTs; benefits may persist up to 10 years, and can be reasonably predicted by preoperative use of non-invasive repetitive magnetic stimulation (rTMS). rTMS first developed as a means of predicting the efficacy of epidural procedures, then as an analgesic method on its own right. Reasonable evidence from at least six well-conducted RCTs favors a significant analgesic effect of high-frequency rTMS of the motor cortex in neuropathic pain (NP), and less consistently in widespread/fibromyalgic pain. Stimulation of the dorsolateral frontal cortex (DLPFC) has not proven efficacious for pain, so far. The posterior operculo-insular cortex is a new and attractive target but evidence remains inconsistent. Transcranial direct current stimulation (tDCS) is applied upon similar targets as rTMS and eMCS; it does not elicit action potentials but modulates the neuronal resting membrane state. tDCS presents practical advantages including low cost, few safety issues, and possibility of home-based protocols; however, the limited quality of most published reports entails a low level of evidence. Patients responsive to tDCS may differ from those improved by rTMS, and in both cases repeated sessions over a long time may be required to achieve clinically significant relief. Both invasive and non-invasive procedures exert their effects through multiple distributed brain networks influencing the sensory, affective and cognitive aspects of chronic pain. Their effects are mainly exerted upon abnormally sensitized pathways, rather than on acute physiological pain. Extending the duration of long-term benefits remains a challenge, for which different strategies are discussed in this review.

Training in the practice of noninvasive brain stimulation: Recommendations from an IFCN committee

As the field of noninvasive brain stimulation (NIBS) expands, there is a growing need for comprehensive guidelines on training practitioners in the safe and effective administration of NIBS techniques in their various research and clinical applications. This article provides recommendations on the structure and content of this training. Three different types of practitioners are considered (Technicians, Clinicians, and Scientists), to attempt to cover the range of education and responsibilities of practitioners in NIBS from the laboratory to the clinic. Basic or core competencies and more advanced knowledge and skills are discussed, and recommendations offered regarding didactic and practical curricular components. We encourage individual licensing and governing bodies to implement these guidelines.

Effectiveness of tonic and burst motor cortex stimulation in chronic neuropathic pain

Background: Motor cortex stimulation (MCS) is an intracranial, invasive method for treatment of chronic pain. Main indications for MCS are central post stroke pain, neuropathic facial pain, phantom limb pain and brachial plexus or spinal cord injury pain. Spinal cord stimulation (SCS) with burst waveform has been proved to be more effective than tonic mode in chronic pain. Necessity to replace depleted batteries of motor cortex tonic stimulators gave us an opportunity of applying burst stimulation. The objective of the pilot study was to evaluate the effects of burst stimulation applied on motor cortex in patients with chronic pain syndromes as well as comparison to tonic mode. Materials and methods: We have evaluated 6 patients (females N=3, males N=3) belonging to the group of 14 cases (females N=5, males N=9) who had undergone surgical procedure of MCS in years 2005-2017. Selected for the study were 6 patients with thalamic pain N=3, with facial pain N=3 (anaesthesia dolorosa and neuropathic trigeminal neuralgia). The patients were subjected to both modes of stimulation then they chose which one was better in relieving pain: tonic or burst. Pain intensity was assessed with the visual analogue scale (VAS) before the replacement of implanted pulse generator (IPG) and after the stimulation with tonic and burst modes. Results: In the study, 5 out of 6 patients with MCS found burst mode more effective than tonic mode. Baseline VAS score in patients that had at least 3 months depleted battery of tonic IPG was 95 mm. After implantation of a new IPG mean VAS score on tonic stimulation was 72 mm, on burst 53 mm. Conclusions: The most preferred option of MCS in selected group of patients was burst stimulation. This study has shown, that the burst stimulation of cerebral cortex is a promising modality when tonic stimulation is not sufficient in refractory, neuropathic pain.

[Motor cortex stimulation in deafferentation facial pain]

OBJECTIVE

To demonstrate the results of treatment of poorly controlled deafferentation facial pain using motor cortex stimulation and to review the relevant literature.

MATERIAL AND METHODS

The study included 8 patients (3 males and 5 females) with deafferentation facial pain who were implanted with a system of constant motor cortex stimulation at the Illinois University in Chicago in 2004-2016 and Novosibirsk Federal Center of Neurosurgery in 2017. The patients' age ranged from 37 to 81 years (mean age, 57.5 years). Scale-based assessment of the pain severity was performed at admission to hospital, at discharge, and during follow-up. The visual analogue pain scale, Barrow Neurological Institute pain scale (BNIPS), and McLaughlin scale were used.

RESULTS

Immediately after surgery, a significant improvement in the form of pain reduction by 80-100% occurred in 4 patients. The pain intensity at discharge from the hospital decreased by 55%, on average. During the follow-up period, the efficacy of motor cortex stimulation was assessed (McLaughlin scale) as very good by 3 of the 8 patients, as good by 4 patients, and as unsatisfactory by 1 patient.

CONCLUSION

Our findings and recent studies have demonstrated that motor cortex stimulation is one of the treatment options for deafferentation facial pain. Even a slight decrease in the intensity of excruciating and debilitating pain (assessed by patients as a good effect) gives grounds for application of the procedure. Further research is needed to define more precise criteria for selecting patients for this treatment and to increase the efficacy of stimulation.

Modelling of the Current Density Distributions during Cortical Electric Stimulation for Neuropathic Pain Treatment

In the last two decades, motor cortex stimulation has been recognized as a valuable alternative to pharmacological therapy for the treatment of neuropathic pain. Although this technique started to be used in clinical studies, the debate about the optimal settings that enhance its effectiveness without inducing tissue damage is still open. To this purpose, computational approaches applied to realistic human models aimed to assess the current density distribution within the cortex can be a powerful tool to provide a basic understanding of that technique and could help the design of clinical experimental protocols. This study aims to evaluate, by computational techniques, the current density distributions induced in the brain by a realistic electrode array for cortical stimulation. The simulation outcomes, summarized by specific metrics quantifying the efficacy of the stimulation (i.e., the effective volume and the effective depth of penetration) over two cortical targets, were evaluated by varying the interelectrode distance, the stimulus characteristics (amplitude and frequency), and the anatomical human model. The results suggest that all these parameters somehow affect the current density distributions and have to be therefore taken into account during the planning of effective electrical cortical stimulation strategies. In particular, our calculations show that (1) the most effective interelectrode distance equals 2 cm; (2) increasing voltage amplitudes increases the effective volume; (3) increasing frequencies allow enlarging the effective volume; and (4) the effective depth of penetration is strictly linked to both the anatomy of the subject and the electrode placement.

Cyclization of Motor Cortex Stimulation for Neuropathic Pain: A Prospective, Randomized, Blinded Trial

OBJECTIVES

Programming guidelines for motor cortex stimulation (MCS) in neuropathic pain requires further investigation. After optimizing voltage as a percentage of motor threshold, we evaluated the effect of cyclizing time of stimulation on pain relief for chronic neuropathic pain.

METHODS

Six patients were enrolled into this trial. In a prospective, randomized, double-blinded manner, patients were programmed to receive stimulation 100, 83.3, 66.7, or 50% of the time in 30-min intervals. Outcomes were assessed after 14 days on each setting with a visual analogue scale (VAS) for pain and the SF36 quality of life questionnaire.

RESULTS

There was no significant difference (p > 0.05) between the different cyclized settings as measured by the VAS, MGPQ, or SF36 in our cohort. There were two distinct subgroups: responders (n = 4) and nonresponders (n = 2) to cyclization. Responders continued to have pain relief when stimulation was reduced to only 50% of the time (15 min ON/15 min off). Interestingly, this group subjectively preferred the 50% stimulation timing compared to 100%. Nonresponders could not tolerate cyclizing because of increased pain.

CONCLUSIONS

In this small cohort, cyclization of MCS settings revealed two distinct subgroups: responders and nonresponders. Responders tolerated stimulation in all settings and 50% stimulation (15 min ON/15 min off) was their subjectively preferred setting. Cyclization in responders will prolong battery life and delay the need for INS replacement and may offer improved pain relief. Building from our previous work, we recommend clinicians consider following the Vancouver MCS programming algorithm presented in this manuscript.

Deep brain stimulation versus motor cortex stimulation for neuropathic pain: A minireview of the literature and proposal for future research

The treatment of neuropathic pain remains a public health concern. A growing cohort of patients is plagued by medically refractory, unrelenting severe neuropathic pain that ruins their quality of life and productivity. For this group, neurosurgery can offer two different kinds of neuromodulation that may help: deep brain simulation (DBS) and motor cortex stimulation (MCS). Unfortunately, there is no consensus on how to perform these procedures, which stimulation parameters to select, how to measure success, and which patients may benefit. This brief review highlights the literature supporting each technique and attempts to provide some comparisons and contrasts between DBS and MCS for the treatment of neuropathic pain. Finally, we highlight the current unanswered questions in the field and suggest future research strategies that may advance the care of our patients with neuropathic pain.