Very low frequency (<2 Hz) stimulation may be more effective at controlling neuropathic pain in patients with spinal-cord injury than higher frequencies (>10 Hz), according to a small, 2-subject study presented on September 28 at the 140th Annual Meeting of the American Neurological Association (ANA).
Corneliu Luca MD, PhD, University of Miami Health System, Miami, Florida and colleagues observed 2 patients with severe pain from longstanding spinal-cord injury. The patients received deep-brain stimulation (DBS) in the midbrain periaqueductal and periventricular gray areas. The patients could optimise analgesia by selecting the 1 resulting in the greatest pain relief from among several blinded frequencies.
One of the participants has a partially severed spinal cord between the T10 and T11 vertebrae, and showed almost complete analgesia when applying the lowest stimulation frequencies (mean 0.67 Hz). The other participant has a completely severed spinal cord (at C4), and experienced minimal pain relief, but also preferred 0.67 Hz over higher frequencies.
In both of these patients, visual side-effects, the only complication of stimulation, disappeared with lower frequencies. After adjustment of frequency, pain could change over several hours or more, indicating the value of slow titration.
These findings suggest that very low frequencies should be applied “whenever DBS is used for prolonged, continuous direct excitation of a pathway,” the researchers concluded.
Dr. Luca also noted that this was the first time very low frequency stimulation of brain nuclei was used to treat pain in patients with spinal-cord injury. “Our results may affect the way clinicians treat pain in patients with spinal-cord injury in the future,” he said.
Randomised, controlled trials are required to confirm these findings.
DBS of the periaquedactal gray and periventricular gray matter has been used for several decades to control chronic pain, including neuropathic pain experienced by patients after spinal-cord injury.