The operation Motor Cortex Stimulation or MCS was developed in Japan in the 1980’s to treat post-stroke pain. It is performed in specialized centres around the world. It is not a particularly demanding neurosurgical procedure and as such has relatively few complications. The most difficult aspect of this operation is selecting the correct patient. In the treatment of pain, it is widely accepted that a ‘successful’ procedure (or pill) is one that reduces the pain by more than 50%. With this standard, MCS has a success rate of approximately 50% for pain in the body and 70% for pain in the face.
This operation is performed under a general anesthetic with electrophysiological monitoring. The scalp is incised and a small window of skull removed. An electrode is placed on the dura (the leather-like covering over the brain) directly over the motor cortex. The skull and scalp are closed and the electrode is connected by a wire to a pacemaker, which is placed under the skin in the chest (or a convenience site). After the operation, the stimulation from the pacemaker is directed through the wire to the electrode over the motor cortex. Stimulating the motor cortex is thought to ‘down regulate’ the abnormal brain activity causing the pain syndrome. How this occurs is still debated. Activity in the motor cortex (the part of the brain initiating movement) is known to down regulate the sensation from the part of the body moving. For example, someone throwing a spear cannot feel fine touch in the hand throwing the object as well as if their hand was still. This may have provided an evolutionary advantage on the African savanna millions of years ago. We know that the sensory system is abnormally up regulated when someone has neuropathic pain. The drugs that treat neuropathic pain all tend to dampen the function of the nervous system – but unfortunately their sedative side-effects are predictable. MCS may use this ancient neural pathway from the motor system to quiet the activity in the sensory system.
When this operation is successful, patients report that their pain drops from an average 8 or 9 out of 10 down to a 2 or 3 out of 10. We have not had a patient report that all of their pain has disappeared although there are reports of this in the literature. The potential complications of this operation include infection (1%) or a brief seizure triggered by too much stimulation of the motor cortex. A full description of all potential complications requires direct discussion with your neurosurgeon. After the operation, patients must come to the clinic for adjustment of their stimulation on a monthly basis for several months. Eventually the pacemaker will run out of power and need elective replacement. This is done as an outpatient procedure under local anesthetic and usually takes twenty minutes of operating time.