Noninvasive transcranial direct current stimulation of the pain-modulating areas of the cerebral cortex markedly reduced postoperative pain and opioid use in a randomized trial involving total knee arthroplasty recipients.
Transcranial direct current stimulation (tDCS), a novel and apparently safe form of neurostimulation for analgesia, also is in planned or ongoing clinical trials for various forms of chronic pain.
Dr. Jeffrey Borckardt
In tDCS, two saline-soaked electrodes are placed over different areas of the brain so that a 2.0 mA direct current can be run through the brain for about 20 minutes. This electrical current increases activity in one target area of the brain while decreasing activity in another. In the total knee arthroplasty study, for example, the cathode was placed over the right dorsolateral prefrontal cortex, and the anode was placed over the knee representation of the motor strip.
There is intense research interest in extending tDCS beyond the arena of pain control and exploring its potential for nonpharmacologic treatment of mood and anxiety disorders, according to Jeffrey J. Borckardt, Ph.D., a psychologist at the Medical University of South Carolina, Charleston.
“This whole area of minimally invasive brain stimulation technologies is growing rapidly. Psychotherapy changes the electrical patterns that are realized in the brain, as shown by good-quality functional MRI studies. And tDCS is another way to do that,” he explained. “We’ve just started playing with an idea that has real interesting potential: If we can enhance cortical excitability in targeted brain regions and we also have an idea what we’re doing to brain regions with psychotherapy, we may be able to get a synergistic effect by combining these brain stimulation technologies with psychotherapy. Perhaps we can increase the longevity and even the intensity of the clinical impact we have.”
He and his coinvestigators selected total knee arthroplasty for a pilot clinical trial of tDCS for acute pain because it’s one of the most frequently performed orthopedic surgeries and the postoperative pain is severe. Many patients experience continued marked pain despite opioids and nerve blocks. The result is slowed recovery, increased hospital length of stay, and difficulty in completing the recommended postop physical therapy program.
Dr. Borckardt reported on 40 patients undergoing unilateral total knee arthroplasty who were randomized to receive four 20-minute sessions of real or sham tDCS. The first session was immediately after the surgery, the second 4 hours later, the third on the morning of postoperative day 1, and the fourth that afternoon.
Subjects who received real tDCS used 44% less patient-controlled opioid analgesia during the first 48 hours post surgery. And despite having significantly fewer opioids on board, they rated their pain as significantly less than controls did: an average of 9 out of a possible 100 points on a visual analog scale, compared with 34 points in the sham tDCS group.
In an earlier randomized, sham-controlled pilot study of tDCS for postprocedural pain in 21 women undergoing endoscopic retrograde cholangiopancreatography for pancreatitis-related pain, the patients who received a single 20-minute session of real tDCS used an average of 22% less patient-controlled opioid analgesia (Gastrointest. Endosc. 2011;73:1158-64).
Transcranial direct current stimulation, like the much more extensively studied transcranial magnetic stimulation (TMS), falls under the heading of neurostimulatory therapies for pain control. All rely upon the gate theory of pain, which holds that bombarding pain-signaling pathways with stimuli prevents the pain signals from getting through.
The best-known neurostimulation technology is transcutaneous electrical nerve stimulation (TENS). Invasive neurostimulation technologies include spinal cord stimulation; vagus nerve stimulation, which is Food and Drug Administration–approved for treatment of both epilepsy and depression; and motor cortex stimulation, involving a small craniotomy and implantation of electrodes into the brain.
Dr. Borckardt and his South Carolina colleagues have been heavily involved in studies of both TMS and tDCS. These are noninvasive technologies in that they don’t entail implantation of electrodes or generators. Both can be performed on patients who are awake.
Transcranial magnetic stimulation uses a cone-shaped magnetic field generated by a figure-eight–shaped coil placed above the patient’s head. The magnetic field passes unimpeded through the hair and skull to depolarize neurons in a dime-sized target area. However, if the magnetic field intensity or frequency is too high, the therapy can induce seizures. The therapy also causes bone pain or discomfort. Although Dr. Borckardt characterized TMS as “reasonably safe,” tDCS is a considerably safer procedure because it doesn’t depolarize neurons and thus doesn’t cause seizures or other adverse effects.
It is also much easier to perform tDCS than TMS. Among other attractive features of the nonpharmacologic therapy is that electricity has no metabolite or other residue, the psychologist noted. But he was quick to add that research into the modern clinical applications of this technology is a recent development.
“We’re not really sure of the best way to do tDCS: the best targets, best intensities, best frequencies. But we’re getting there quickly,” Dr. Borckardt said.
He reported having no financial conflicts.