Transcranial Magnetic Stimulation for the Treatment of Phantom Pain

Overview

Phantom pain refers to the sensation of pain felt by patients who have had a limb amputated. The treatment of phantom pain is often disappointing and is unable to provide adequate relief to the patients. The area of the brain involved (posterior parietal cortex \[PPC\]) is found on the opposite side of the amputated limb. For example, if a patient has the right arm amputated, the left posterior parietal cortex is involved in the phantom pain. Researchers believe that if they can decrease activity in the posterior parietal cortex they may be able to reduce phantom pain. Researchers plan to use low frequency (1 Hz) transcranial magnetic stimulation (TMS) to decrease the excitability of the PPC opposite the side of the amputated limb. TMS involves the placement of a cooled electromagnet with a figure-eight coil on the patient's scalp and turning on the magnetic flux. This permits non-invasive, relatively localized stimulation of the surface of the brain (cerebral cortex). When an area of the brain is stimulated a period follows when that area cannot be stimulated again. In this case, researchers plan to use TMS to stimulate the PPC in order to decrease the level of excitability there.

Phantom pain is a chronic painful condition that affects patients with amputations. Treatment for phantom pain is often disappointing. In amputees, hyperexcitability of the posterior parietal cortex area (PPC) contralateral to the side of the amputation has been linked with the presence of phantom sensations. PPC is an area overactive in different forms of chronic pain too. It is therefore conceivable that downregulation of activity in PPC could improve phantom limb pain, a condition poorly responsive to available treatments. We have previously demonstrated that low frequency TMS (1 Hz) results in decreased excitability of the stimulated cortical regions. We plan to apply low-frequency TMS to PPC cortical areas contralateral to the side of the amputated limb. We expect that this intervention will result in amelioration of the phantom pain. Stimulation of the PPC area (target intervention) will be compared with a control intervention in which TMS is directed slightly away from the head.