Motor Cortex Stimulation Provides Long-Term Analgesia for Neuropathic Pain
APRIL 08, 2014
Amber N. Mitchell, MD
Epidural motor cortex stimulation (MCS) is an alternative, adjuvant treatment for intractable neuropathic central pain. MCS consists of invasive implantation of a device epidurally with continuous stimulation at frequencies that serve to supplement conventional pharmacologic analgesics. Prior studies have shown that positive analgesic response to noninvasive repetitive transcranial magnetic stimulation (rTMS) serves as an adequate preoperative predictor of continuous MCS efficacy. 1-3 Therefore, an analgesic effect of noninvasive rTMS often serves as an aid to identify candidates for invasive epidural implantation of the MCS apparatus. However, some studies have shown that a poor rTMS response may fail to identify some successful responders to subsequent MCS.4
With this in mind, the authors of “Is Life Better after Motor Cortex Stimulation for Pain Control? Results at Long-Term and their Prediction by Preoperative rTMS,” published in Pain Physician, sought to clarify the predictive value of rTMS with respect to MCS and to assess long-term pain reduction and quality of life scores in a blinded fashion.
For the study, 20 patients (mean age 54.3 years, 45% female), were randomized to two cohorts of sham vs. active 20Hz-rTMS in a cross-over model, before all patientswere submitted to MCS surgery. There was a statistically significant pain reduction of 14.6% for active rTMS versus 2.9% for the sham group. Effects of MCS at six months and six years were included. Fifty percent of patients retained long-term benefit of MCS by both intensity and quality of life assessments (ability to function free of pain and dependence).
The results of this study showed that MCS was beneficial regardless of previous response to non-invasive preliminary rTMS, although positive response to a single session of rTMS by combined pain assessment and henceforth long-term response to continuous MCS had a 90% positive predictive value (PPV) and 67% negative predictive value at long-term assessments.
Transcranial magnetic stimulation was independently efficacious (14.6% vs. 2.9% pain reduction for sham) outside of response to MCS at 6 months and mean 6 years (37% and 28%, respectively). However, those who did experience analgesic effect from rTMS were more likely to benefit from MCS with a 90% PPV.