Motor cortex stimulation may improve chronic pain

Clinical question Does motor cortex stimulation improve chronic pain?

Bottom line The reporting of this systematic review limits the conclusions, but it appears that motor cortex stimulation decreases pain in patients with chronic pain. The inclusion of lower-quality studies and the incomplete reporting makes it difficult to determine if the improvement is clinically important. (Level of evidence = 2a–)

Synopsis The authors searched several databases for prospective studies that evaluated the effectiveness of motor cortex stimulation in patients with chronic pain. Additionally, the authors tried to find unpublished studies. The authors don't describe independent selection of the included studies, study quality assessment, or data extraction. They included 22 studies (327 patients) of invasive brain stimulation and 11 studies (274 patients) of noninvasive stimulation. In other words, these were all small studies. Some of the studies were open-label trials, a design that tends to make the intervention look better. The authors report that pain was significantly reduced by 9.4% using a visual analog scale. They also provide a great deal of data about the proportion of responders in the various studies, but fail to define what constitutes a response. They also fail to report the response rate in the control groups. The response rate is greater in the invasive studies than in the noninvasive studies, but because we don't know the control rate, we don't know how much better these interventions really are.

Lima MC, Fregni F. Motor cortex stimulation for chronic pain: systematic review and meta-analysis of the literature. Neurology. 2008;70(24):2329-2337.