Deep brain stimulation for chronic pain: a narrative review.

Although Deep brain stimulation (DBS) is commonly used in movement disorders, it was originally developed in the 1970s to treat medically-refractory chronic pain. There are still indications for DBS, including refractory facial neuropathic pain, central neuropathic pain, brachial plexus avulsion pain, and phantom limb pain. Brain DBS targets used to treat pain are either involved in nociception pathways, belonging to the "Pain Matrix", such as the sensitive nuclei of the thalamus, the insula or the anterior cingulate; or are involved in pain inhibitory pathways such as the periaqueductal and periventricular grey matters (PAG/PVG). The effect and efficacy of PAG/PVG-DBS, mainly used to treat nociceptive pain, and thalamic-DBS (used more in neuropathic pain) were described in case series, showing an overall 63% success rate in nociceptive pain and 47% in neuropathic pain. Recently, new targets have been proposed, including the anterior cingulate and insula. Each of these targets has shown varied outcome that are described and discussed in this review. DBS remains a therapeutic option for patients suffering from severe chronic neuropathic pain resistant to pharmacological and non-pharmacological treatments. Its results encourage the continued use of DBS in therapeutic trials to optimize targets, improve patient selection and determine optimal stimulation modalities.