Deafferentation pain: Cerebral cortex surgery

Abstract

Deafferentation pains are very difficult to treat by medication and surgical techniques, and there is no established strategy. Until today, many kinds of ablation surgeries were tried for deafferentation pains. Now electrical stimulation therapies (spinal cord stimulation, deep brain stimulation and motor cortex stimulation) are currently used, because these techniques are less invasive and more effective. At this time, I would like to summarize the current treatments and discuss cortical (motor cortex) stimulation therapy (MCS). MCS has been reported to be effective on thalamic pain, phantom limb pain and CRPS. As a standard MCS technique, a resume was placed in the epidural space with SEP measuring to determine the central sulcus. We placed a grid electrode in the subdural space to decide upon the best stimulation point for pain relief over a few weeks with the purpose of determining the placement of a resume. In several patients, resumes were implanted in the interhemispheric fissure to reduce lower extremity pain. In seven patients, resumes were placed within the central sulcus to stimulate area 4 and area 3b directly. In addition, electrodes were also placed on the surface of the precentral gyrus. To date, 75% of the patients in our institute showed pain reduction. Our results indicated that area 4 within the central sulcus may be the optimal stimulation point for pain relief. We speculate that conventional method may sometimes fail to stimulate area 4 and that focal stimulation of area 4 within the central sulcus may improve the efficacy of this treatment. Our pharmacological tests show that the mechanism of deafferentation pain seems to be complicated, but patients with ketamine sensitivity seem to be good candidates for MCS. The MCS mechanism is unknown. A study with positron emission tomography showed that CBF increases in the thalamus, anterior cingulate, rectal gyrus and brainstem after MCS, but rarely in the sensory cortex. The efficacy of MCS is mainly related to increased synaptic activity in the thalamus, while activations in the rectal gyrus, anterior cingulate and frontal cortex may be rather related to emotional processes. MCS is a good and less invasive treatment for deafferentation pain, especially for thalamic pain, but the success rate is not 100%. In the case of MCS failure, we should choose spinal cord stimulation and deep brain stimulation especially for peripheral deafferentation pain.