Motor Cortex Stimulation for Intractable Pain

Richard K. Osenbach, M.D.

Disclosures

Neurosurg Focus. 2006;21(6) 

In This Article

Transcranial Magnetic Stimulation

Although pharmacological testing can provide important information regarding which patients might respond to MCS, it is not ideal and obviously does not correctly predict outcome in all patients. Transcranial magnetic stimulation is a tool that has been used in a wide variety of neurological disorders, for experimental, diagnostic, and therapeutic purposes. The TMS procedure produces a magnetic field that traverses the skull relatively unimpeded and induces an electrical field that yields actual brain stimulation (Fig. 2). Because TMS is noninvasive and painless, it can be easily performed in awake patients. Repetitive TMS has been investigated as a potential therapy in patients with medically intractable neuropathic pain.[5,16] Based on its known mechanisms of action, TMS could be used preoperatively to screen patients for MCS.

Figure 2.

Photograph showing the TMS device, which may be used preoperatively as a potential predictor of the response to MCS.

Drouot and colleagues[5] studied 12 patients with neuropathic pain by using repetitive TMS. All patients suffered from chronic unilateral neuropathic pain involving the face and/or hand; the pain was due to thalamic infarction (four patients), trigeminal nerve lesions (three), or brachial plexus avulsion (five). The TMS technique was performed with a figure-eight coil positioned on the area of the scalp overlying the motor cortex corresponding to the painful region. Patients underwent three sessions of stimulation: 1) a 20 train series for 5 seconds, frequency of 10 Hz, intensity at 80% of motor threshold; 2) a protocol identical to the first one, but using a "sham" coil; and 3) 0.5-Hz stimulation for 20 minutes at 80% of motor threshold intensity. Patients were asked to rate their pain on a 0- to 10-point VAS before and 10 minutes after concluding TMS.

The investigators observed no adverse effects of TMS. With sham stimulation, there was no significant difference in pre- and posttreatment VAS scores (7.0 ± 0.6 compared with 6.5 ± 0.6, p = 0.28). Stimulation at 0.5 Hz produced minimally significant changes in VAS scores (6.4 ± 0.7 compared with 5.5 ± 0.7, p = 0.04), whereas the reduction in VAS scores with 10-Hz stimulation was significantly more dramatic (7.3 ± 0.5 compared with 4.8 ± 0.8, p = 0.0005). The results of this study indicated that TMS of the motor cortex can produce at least transient pain reduction that appears to be largely frequency dependent. With more data, it is conceivable that TMS could become an important preoperative screening tool for patients undergoing MCS.

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