Surgical treatment for central pain after stroke based on the neural mechanism

Abstract

Previous neurophysiological and neuroimaging studies have suggested that functional changes might occur in the sensory thalamus, associated with reorganization of the thalamocortical system, in cases with central pain after stroke (thalamic pain). It might cause the misconduction of the sensory signal or a hyperactive response to peripheral natural stimulation on the thalamus, resulting in it playing an important roles in the genesis of central pain. Hyperactivity in the cerebral cortex adjacent to the central sulcus on the side ipsilateral to a cerebrovascular disease (CVD) lesion also might relate to central pain. We performed various kinds of surgical treatments in 29 cases with central pain after stroke based on the neural mechanism deserbed above. Epidural spinal cord stimulation was effective in 4 out of 7 cases with localized pain on the distal part of the leg and arm. We achieved pain control in these cases showing definite SEP originating in the sensory cortex before surgery. Stereotactic (Vim-Vcpc) thalamotomy with the aid of depth microrecording was effective in 4 out of 7 cases with diffuse pain. In good responders, we could find responses to natural peripheral stimulation and seldom encountered irregular burst discharges in the sensory thalamus during the operation. Preoperative PET studies also revealed an increase of rCBF in the sensory cortex ipsilateral to the thalamic CVD lesion during contralateral thumb brushing. Gamma knife treatment was effective in 5 out of 7 cases after stereotactic thalamotomy. It became stable in 3 out of these 5 cases. Each case was treated with a maximum dose of 120∼ 150 Gy using a 4 mm collimator. Precentral electrical cortical stimulation was performed in 8 cases. Sufficient pain relief was achieved in 3 out of 6 cases in which we could implant an IPG. In one of these cases, we found definite sensory responses and seldom encountered irregular burst discharges in the sensory thalamus during the previous thalamic surgery. A MEG study also demonstrated preservation of spino-thalamo-cortical function in the other one case. In each case, in which we failed to achieve pain control, internal capsular (posterior limb) or thalamic Vim-Vcpc stimulation was carried out. We could obtain sufficient but short-term pain relief. Surgical treatment could be expected to ameliorate central pain after stroke in those cases in which CVD had caused mild destruction of the pain conducting system and the spino-thalamo-cortical function was relatively preserved.