Practical Pain Management 2022 September/October;22(5)
Studies on brain stimulation for pain began in the 1950s, when researchers looked at its potential for treating pain associated with spinal cord and back injuries. While some findings on the use of brain stimulation for pain have been promising, results have been mixed, and in the US, deep brain stimulation for chronic pain remains investigational. However, the relative lack of safe and effective methods of treating long-term pain has led to a resurgence of interest in the modality.
In a paper published in July 2022 in Neurosurgery Clinics of North America, Alexander Alamri, MBBS, BSc, and Erlick A. C. Pereira, BMBCh DM, of the Neurosciences Research Centre, Molecular and Clinical Sciences Research Institute, at St. George’s University London, took a close look at the current body of literature on the use of DBS for pain, highlighting its risks and benefits. Based on that review, they offered suggestions and best practices for using DBS to treat chronic pain going forward.
Alamri and Pereira pointed out that there is no generally accepted agreement on the mechanism of action behind DBS beyond its effects at the neuronal level. It is possible, they noted, that DBS disrupts high-frequency synchronous oscillations or boosts low-frequency oscillations in parts of the reticulo-thalamic-corticofugal pain neuromatrix.
Regardless of the mechanism of action, careful choice of targets is essential. Their literature review found several targets for DBS, but they emphasized the following: the anatomic target for DBS is generally accepted as a basis for placement of the electrode, but the selection of the final target is more complex and requires physiologic mapping and clinical assessment.
They noted several studies where DBS was found to be effective for chronic pain when using three main targets:
- the periaqueductal gray matter/periventricular gray matter (PAG/PVG)
- the ventral posterior medial/ventral posterior lateral (VPM/VPL) nuclei
- the anterior cingulate cortex (ACC)
The process of screening patients with chronic pain for suitability of DBS should be carried out by a pain physician, wrote Alamri and Pereira. A psychological assessment may also be necessary.
The authors warned that it is important to accurately diagnose anatomic pathologies of chronic pain, such as spondylotic disease, before proceeding with any treatment and that conventional and/or interventional treatments be trialed first, as DBS remains off-label. In certain cases, they wrote, DBS may be appropriate for individuals who have not found relief from conservative or first-line therapies, such as SCS for failed back surgery syndromes.
Dr. Raslan agrees that it’s possible DBS could be effective for certain patients and certain parts of the brain, but he pointed out, the pain community has not identified these targets yet.
Care should be taken when placing a DBS electrode, and it should be tested to ensure correct placement, the reviewers advised. Complications from DBS are low but still worth discussing with patients. Potential risks include hemorrhage, infection, and erosion of the skin over the implant.
However, tolerance may develop several years after DBS treatment. The authors suggested that tolerance may be overcome by making slight changes in the stimulation settings or even by periodically interrupting the stimulation. In addition, technological advancements, such as adaptive stimulation, are in the works and may help to overcome these limitations.
Alamri and Pereira summarized their review by recommending that researchers demonstrate the efficacy of DBS as a treatment for chronic pain. At the same time, they emphasized that, because DBS can be switched on and off, RCTs with smaller populations can still be informative.
Dr. Raslan added that there is hope for the approach but cautions that the pain community needs to better understand how pain is coded in the brain before it can be altered. “Pain is a very complex sensation with multiple aspects: an emotional component, the sensory component, and cognitive component,” he explained. “These are three different networks in the brain and targeting one network would not suffice. You have to target multiple networks. It’s also possible that certain pain types are more amenable to treatment than others, such as neuropathic pain versus nociceptive pain.”