Motor Cortex Stimulation for Intractable Pain

Richard K. Osenbach, M.D.

Disclosures

Neurosurg Focus. 2006;21(6) 

In This Article

Programming and Patient Follow-Up Evaluation

There is wide variability in the stimulation parameters used for long-term MCS ( Table 4 ). A standardized protocol for long-term stimulation has yet to be developed, and quite frankly it may not be possible to develop "standard" stimulation parameters that will be suitable for all patients. Therefore, parameters for chronic stimulation should be chosen that result in the best pain relief. Although some patients can obtain excellent pain relief with the initial parameters, experience has suggested that a number of these patients require frequent adjustments to maintain efficacy. Bipolar stimulation is used, and because the electrical field is generated at the negative pole, the cathode overlies the motor cortex and the anode the sensory cortex. At our institution we generally begin by programming the IPG with parameters similar to the ones that produced the best results during the trial. Most patients begin with a rate of 50 Hz and a pulse width of 200 msec. The amplitude can be programmed at either the minimum intensity required for pain relief or as a percentage of the intensity that corresponds to the motor threshold. No data as yet suggest that one method is superior to the other. If the latter method is used, one obviously must identify the motor threshold, and in doing so induction of a seizure is more likely. In most patients, pain relief occurs within minutes, and the effect persists for minutes to hours after stimulation is discontinued.

One of the advantages of MCS over other neurostimulation techniques such as SCS is that analgesia is not dependent on perception of paresthesias. Spinal cord stimulation is rarely if ever effective in patients who lack the ability to perceive stimulation-induced paresthesias, as is the case in those who suffer from full-blown anesthesia dolorosa, phantom pain, or other deafferentation pain syndromes that have rendered the painful area anesthetic. Because MCS does not depend on paresthesia perception, it can potentially be effective in conditions that will not respond to more conventional neurostimulation techniques. For many patients, analgesia is the only indication that the stimulator is on. Some patients may experience paresthesias located in the distribution of their pain, but this varies.

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