Cortical neurostimulation for neuropathic pain

Abstract

The treatment of neuropathic pain by neuromodulation is an objective for more than 40 years in modern clinical practice. With respect to spinal cord and deep brain structures, the cerebral cortex is the most recently evaluated target of invasive neuromodulation therapy for pain. In the early 90s, the first successes of invasive epidural motor cortex stimulation (EMCS) were published. A few years later was developed repetitive transcranial magnetic stimulation (rTMS), a noninvasive stimulation technique. Then, electrical transcranial stimulation returned valid and is currently in full development, with transcranial direct current stimulation (tDCS). Regarding transcranial approaches, the main studied and validated target was still the motor cortex, but other cortical targets are under investigation. The mechanisms of action of these techniques share similarities, especially between EMCS and rTMS, but they also have differences that could justify specific indications and applications. It is therefore important to know the principles and to assess the merit of these techniques on the basis of a rigorous assessment of the results, to avoid fad. Various types of chronic neuropathic pain syndromes can be significantly relieved by EMCS or repeated daily sessions of high-frequency (5-20 Hz) rTMS or anodal tDCS over weeks, at least when pain is lateralized and stimulation is applied to the motor cortex contralateral to pain side. However, cortical stimulation therapy remains to be optimized, especially by improving EMCS electrode design, rTMS targeting, or tDCS montage, to reduce the rate of nonresponders, who do not experience clinically relevant effects of these techniques.

Delayed pain decrease following M1 tDCS in spinal cord injury: A randomized controlled clinical trial

“…This observation highlights the long-term effects of tDCS in maintaining low level of pain as compared to the sham intervention. As abovementioned, several studies have highlighted the need for repeating the number of tDCS sessions (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) to induce long-lasting and clinically relevant effects. In the present study, even with a limited sample size, we demonstrated that adding a second phase of 10 stimulations sessions can help maintaining the benefits induced by tDCS.…”

“…Robust and extensive basic science research has demonstrated the effects of tDCS and many studies have confirmed that the anode increases cortical excitability while the cathode decreases it [8,10,11]. From a clinical perspective, when the anode is placed over the primary motor cortex (M1), it can induce clinically significant pain relief in chronic pain syndromes [7,[12][13][14][15][16]. In a previous study, our group has tested the effects of tDCS in SCI patients suffering from neuropathic pain, showing that 5 sessions of M1 tDCS significantly reduced level of pain after the end of the stimulation sessions but not when reassessed at 2-week follow-up [7].…”

Strategies for replacing non-invasive brain stimulation sessions: recommendations for designing neurostimulation clinical trials

“…In studies detailing missing visits, the rate of patients who were not fully adherent is extremely high, ranging from 30 to 60%, reflecting the importance of taking this factor into account when designing a trial and when reporting the results. Although it is well-defined that multiple sessions of tDCS and TMS have cumulative effects, the impact of spaced sessions in abolishing, potentiating or having no effect still needs to be further clarified [16,[33][34][35]. This was explored by Zanão et al (2014), based on their previous trial [36] where some patients did not attend all visit [37].…”

“…missed visits) [11,12]. In addition, these disorders are frequently studied in neurostimulation trials which have shown promising results for symptom reduction (for reviews see [13][14][15][16][17]). Based on our findings, we proposed a strategy to handle these missed visits.…”

Electronic Dura Mater Meddling in the Central Nervous System

“…7 Motor cortex stimulation delivered over the epidural surface has emerged as a potential strategy to treat resistant peripheral and central neurogenic pain resulting from stroke or trigeminal neuropathy. 15 Imaging studies 16 suggest that motor cortex stimulation inhibits the high firing rate of the sensory compartment of the thalamus and increases the activity of the cingulate gyrus, which together diminish pain. In present applications, electrodes are positioned epidurally.…”