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HomeBrainindex/list_12253_1Motor Cortex Stimulation for Chronic Neuropathic Pain

Motor Cortex Stimulation for Chronic Neuropathic Pain

Abstract and Introduction

Abstract

Motor cortex stimulation via surgically implanted electrodes has been used as an off-label treatment for chronic neuropathic pain, but its efficacy has not been fully established. We aimed to objectively study the efficacy of motor cortex stimulation and characterize potential predictors of response.

In this randomized, double-blind, sham-controlled, single centre trial, we recruited 18 patients with chronic neuropathic pain who did not adequately respond to conventional treatment and had a numerical pain rating scale (NRS) score ≥6. Patients were initially assigned to receive 3 months of active (‘on’) or sham (‘off’) stimulation in a double-blind cross-over phase. This was followed by a 3-month single-blind phase, and 6 months of open-label follow-up. A meaningful response in our trial was defined as a ≥30% or 2-point reduction in NRS scores during active stimulation.

Using Bayesian statistics, we found a 41.4% probability of response towards on versus off motor cortex stimulation. The probability of improvement during active stimulation (double-blind, single-blind and open-label phases) compared to baseline was 47.2–68.5%. Thirty nine per cent of the patients were considered long-term responders, 71.4% of whom had facial pain, phantom limb pain or complex regional pain syndrome. In contrast, 72.7% of non-responders had either post-stroke pain or pain associated with brachial plexus avulsion. Thirty-nine per cent of patients had a substantial postoperative analgesic effect after electrode insertion in the absence of stimulation. Individuals with diagnoses associated with a good postoperative outcome or those who developed an insertional effect had a near 100% probability of response to motor cortex stimulation.

In summary, we found that ~40% of patients responded to motor cortex stimulation, particularly those who developed an insertional effect or had specific clinical conditions that seemed to predict an appropriate postoperative response.

Introduction

Motor cortex stimulation (MCS) is an invasive neuromodulation technique that has been offered in many centres as a therapeutic alternative to patients with medically refractory chronic neuropathic pain. Despite being used for almost three decades, the effectiveness of MCS remains unclear.[1] A recent review investigating the outcome of MCS for chronic neuropathic pain reported that ~60% of patients had a good postoperative response.[2] To date, only a few clinical trials including double-blind assessments have been published.[3–5] Studies comparing numerical pain rating scale (NRS) scores during active versus sham treatment[3] or high versus low stimulation (longer ‘on’ versus ‘off’ stimulation cycling)[4] found no differences in clinical response. In contrast, a significant analgesic effect of MCS has been reported when stimulation was activated at different intervals.[5]

A major problem in the field of brain neuromodulation for pain is the lack of predictors of a positive outcome. Previously hypothesized factors include an early analgesic effect, clinical diagnosis, the development of an analgesic effect after the insertion of electrodes and electrophysiological responses.[6–9]

We aimed to objectively study the efficacy of MCS and characterize potential predictors of response in a prospective, double-blind, randomized, cross-over trial.

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