Motor cortex stimulation for chronic pain: systematic review and meta-analysis of the literature

To conduct a systematic review and meta-analysis to quantify the efficacy of invasive and noninvasive brain stimulation for the treatment of chronic pain.

MEDLINE and other databases were searched as data sources. Reference lists and conference abstracts were examined for further relevant articles. We included studies that evaluated the effects of invasive and noninvasive brain stimulation of motor cortex on chronic pain using the visual analogue scale. Eleven studies using noninvasive brain stimulation and 22 studies using invasive brain stimulation met our inclusion criteria. The results showed that weighted responder rate was 72.6% (95% CI, 67.7-77.4) for the invasive stimulation studies and 45.3% (95% CI, 39.2-51.4) for the noninvasive stimulation studies. This difference was significant. For the noninvasive stimulation studies, the random effects model revealed that the number of responders in the active group was significantly higher as compared with sham stimulation group (risk ratio of 2.64) (95% CI, 1.63-4.30).

This meta-analysis shows that two different techniques of brain stimulation of motor cortex--invasive and noninvasive--can exert a significant effect on pain in patients with chronic pain. We discuss potential reasons that invasive brain stimulation showed a larger effect in this meta-analysis. Our findings encourage continuation of research in this area and highlight the need for well-designed clinical trials to define the role of brain stimulation in pain management.