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.
Introduction
Some of the neuromodulation techniques may be an adjunct in the treatment of neuropathic pain (NeP) resistant to usual clinical treatment. Despite recent advancements, adequate relief with pharmacological treatments cannot be achieved in up to 40 % of patients (Hansson et al., 2009). Although analgesics, anticonvulsants, antidepressants, and opioids have demonstrated efficacy to several NeP conditions, they often result in insufficient analgesia or intolerable side effects, especially in central NeP (Cruccu et al., 2016). Both invasive and non-invasive neuromodulation techniques have been tested in combination with pharmacological treatments. Some interventions such as transcranial magnetic stimulation have provided an additional 40 to 50 % of pain relief when compared to sham stimulation in patients with central or peripheral neuropathic pain (Baptista et al., 2019, Cruccu et al., 2016, Moisset et al., 2020, Asipp, 2013). Other techniques have been less frequently explored in sham controlled trials as tDCS and SCS. While some of the neuromodulatory techniques enter clinical practice for pain management, issues related to long term efficacy beyond six months, and cost-effectiveness remain to be ascertained...
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