Motor Cortex Stimulation for Intractable Pain

Richard K. Osenbach, M.D.

Disclosures

Neurosurg Focus. 2006;21(6) 

In This Article

Results of MCS

Motor cortex stimulation has proven to be effective in a variety of intractable pain conditions. When interpreting the results of MCS, it is important to consider that this therapy is often applied to some of the most refractory pain problems that exist. Traditionally, a benchmark of 50% pain reduction has been suggested to represent a successful treatment. However, some patients may achieve less than 50% pain relief yet have significant improvement in functional ability and quality of life. Conversely, others may sometimes report high levels of pain reduction yet fail to demonstrate any functional improvement. This dichotomy underscores the need for standardized and valid outcome measures in evaluating not only MCS but all implantable devices for pain therapy.

It would appear that the most consistent success has been achieved in patients with poststroke and trigeminal neuropathic pain. Nguyen et al.[22] reported that 10 of 13 patients with central pain obtained substantial relief with MCS. Katayama et al.[10] reported their results with MCS treatment in 31 patients with poststroke pain with a minimum 2-year follow-up duration. The underlying disorders included thalamic hemorrhage or infarction (20 patients), a small lesion of the posterior limb of the internal capsule (eight), and lateral medullary infarction (three). Of the 31 patients, 24 (77%) achieved sufficient pain control to justify a permanent implant. The initial benefit was maintained throughout the follow-up period in 15 (63%) of the 24 patients who received permanent implants. In eight patients (37%), the effect diminished over time. The absence of significant motor deficits in the painful areas and the ability to elicit motor responses were correlated with a positive effect. Satisfactory pain relief was achieved in 73% of patients in whom motor weakness was absent or only very mild, compared with only 15% of patients with moderate or severe motor weakness. Of the 20 patients in whom motor responses could be elicited, 14 (70%) obtained satisfactory long-term benefit, compared with only one (9%) of 11 patients in whom muscle contraction was not inducible. There was no significant relationship between pain relief and various somatosensory findings. Therefore, an intact corticospinal system originating from the motor cortex appears to be important, at least for patients with poststroke pain, for achieving good pain control with MCS. In some circumstances it is simply not possible to induce motor responses yet MCS can be successful. For example, it has been beneficial in a small number of patients with conditions such as phantom pain and brachial plexus avulsion.[12,27,29] Despite an inability to evoke motor responses, however, these patients would otherwise be anticipated to have had preserved cortical neuronal circuits in the presence of an intact corticospinal pathway.

The second large group of patients for whom MCS appears to be beneficial is those with trigeminal neuropathic pain.[6,15,20] This group includes patients who sustain injury to the peripheral trigeminal system following destructive procedures for trigeminal neuralgia, after resection of tumors that involve the trigeminal nerve or its branches, or as a result of facial trauma, dental procedures, sinus surgery, and so on. Meyerson and colleagues[15] reported one of the first experiences with MCS for trigeminal neuropathic pain in five patients. All had undergone a variety of other treatments, including DBS, stimulation of the Gasserian ganglion, and cervical SCS, without benefit. Motor cortex stimulation provided pain relief varying between 60 and 90% in all five patients. Nguyen, et al.[20] reported significant pain relief in 10 (83%) of 12 patients with neuropathic facial pain.

Recently, other indications for MCS have been identified; these include brachial plexus avulsion, phantom pain, postherpetic neuralgia, and CRPS Type I. Carroll et al.[4] reported relief in excess of 70% in two of three patients with phantom pain. Saitoh et al.[28] described good pain relief in a single patient with this disorder. On the other hand, Katayama, et al.[12] achieved satisfactory long-term pain control in only one of five patients (20%) with phantom pain. Although there have been some encouraging results, there are currently insufficient numbers of patients with these indications to draw any strong conclusions regarding effectiveness.

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