Motor cortex stimulation therapy in patients with thalamic pain

Seven patients with thalamic pain were treated by electrical stimulation of the motor cortex. Patients ranged from 55 to 71 years of age. There were six men and one woman. Causes of thalamic pain were thalamic infarction in 2 patients and thalamic hemorrhage in five. Six patients had intractable pain associated with dysesthesia in the upper and lower limb (upper limb dominant). One patient had intractable pain in the face contralateral to the lesion. Magnetic resonance images (MRI) were performed in 5 patients and showed the deposit of hemosiderin in the internal capsule, posterolateral nucleus and pulvinar. Electrodes were placed on the motor cortex epidurally in seven patients. Electrodes were implanted permanently in six patients and removed in one patient after an unsatisfactory result of test stimulation. Motor cortex stimulation provided satisfactory pain relief in ail six patients for a month after the beginning of stimulation, however, by the time three months had passed, pain relief had become gradually unsatisfactory in five patients. We compared pain relief between 10Hz and 100Hz of stimulus rate in four patients and observed that all patients complained of fatigue in the upper extremity at the 100Hz of stimulus rate, though no difference in pain relief was obtained according to which of these two stimulus rates were used. We concluded that motor cortex stimulation brought about pain inhibition in patients with thalamic pain, but pain control tended to become less gradual within several months after the beginning of stimulation.