Motor cortex stimulation for central pain syndrome treatment

[David Berg]

Someone just emailed this article to me. I subscribe to Medscape, so I don't know how I could have missed it before.

This article is located on Medscape at:
http://www.medscape.com/AANS/NF/2001/v11.n03/nf1103.01.brow/nf1103.01.brow.html

You must have a free account with Medscape to access Medscape online.

David Berg
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From
Neurosurgical FocusTM
Motor Cortex Stimulation for Central Pain Syndromes
Topic Editor: Jeffrey A. Brown, M.D., Department of Neurological Surgery, Wayne State University School of Medicine, Detroit, Michigan
[Neurosurg Focus 11(3), 2001. © 2001 American Association of Neurological Surgeons]

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Technical innovation has been the force that "through the green fuse" drives the flower of progress in the field of neurosurgery. Each of the papers presented in this inaugural symposium on epidural motor cortex stimulation (MCS) reflects this observation. Each article expands on Tsubokawas seminal work published a decade ago in which he treated seven patients with thalamic pain by epidural MCS.

In the opening article the authors summarize the background of discovery that led to the conceptualization of MCS for deafferentation pain. The writers review the conclusions from ensuing publications. Why does MCS help alleviate symptoms in patients with central and neuropathic pain syndromes? Of interest is the work of Garcia-Larrea, et al., Tsubokawa found that MCS increased cerebral blood flow (CBF) in the thalamus and hypothesized that thalamic burst activity was inhibited. Garcia-Larrea, et al., used positron emission tomography to demonstrate that CBF not only increased in the ipsilateral thalamus but also in other sites including the cingulate gyrus, orbito-frontal cortex, and brainstem. The authors correlated the degree of pain relief with the volume of blood flow in the cingulate gyrus. They suggest that MCS improves the suffering component inherent in chronic pain.

There were only a few articles published in the first half decade following Tsubokawa's paper. It was difficult to identify accurately the precentral gyrus while the procedure remains epidural. The far-field, evoked-potential technology used initially to confirm the site of the central sulcus is tedious. Not until Nguyen, et al., applied computer neuronavigation to the task of targeting the precentral gyrus did the field blossom. The operation became much simpler and results improved, especially in patients with facial neuropathic pain, presumably because the cortical facial representation is so much larger and easier to identify. Using neuronavigation for target identification, Nguyen, et al., reported substantial pain relief in patients with central pain and 75% substantial relief in up to 77% of their patients with facial neuropathic pain. This is a major medical breakthrough for conditions thought to be untreatable.

With this background in mind, each of the papers in this issue explores technical variations in the established operative approach. In their paper, "Motor cortex stimulation for deafferentation pain," Saitoh, et al., were unable to confirm any predictive benefit from preoperative pharmacological evaluation in which intravenous phentolamine, ketamine, and morphine are administered, as has been hypothesized by Tsubokawa. They were able to reestablish effective pain relief, which had ceased 6 months after epidural stimulation, by placing a new electrode in the subdural space. They also performed chronic stimulation from within the central sulcus itself. Finally, they expand the indications of treatment to include brachial plexus injury, spinal cord injury, and phantom limb pain.

In the second paper, "Motor cortex stimulation for neuropathic pain," Smith, et al., describe successful alleviation of pain only in patients in whom motor contractions could be elicited by stimulation during their evaluation. They confirm the findings of Katayama, et al., that the presence of moderate to severe paralysis in the region of neuropathic pain correlates with poor postcortical stimulation results.

In their paper, "The Zeiss-MKM system for frameless image-guided approach in epidural motor cortex stimulation for central neuropathic pain," Pirotte, et al., confirm the accuracy of neuronavigation in target identification. The mean distance between magnetic resonance (MR) imaging-defined and the actual central sulcus was 2.4 mm. Intraoperative median nerve evoked potential localization of the central sulcus was, however, not easily reproducible, and it was also less accurate. The authors confirm that their best clinical results were in patients with trigeminal neuropathic and central poststroke pain syndromes.

In the final paper, "Epidural motor cortex stimulation with functional imaging guidance," Mogilner and Rezai introduce the intriguing integration of functional MR imaging and magnetoencephalography for preoperative mapping of the stimulation target. The possibility of precise preoperative target determination based on the individual patient's functional representation rather than a mapped equivalent speaks to a hopeful future concerning this well-established operation for the treatment of patients with a most difficult, and previously untreatable, syndrome.

[This message was edited by David Berg on October 14, 2001 at 01:24 AM.]

[craig]

Huh ? ... LOL http://sci.rutgers.edu/forum/images/smilies/eek.gif

[Joe B]

David

If I understand this summary correctly, several papers reported relieving central pain in test patients (about 75% of patients reported relief) using epidurual motor cortex stimulation. I believe this is electrical stimulation of a precise location of the MC within the brain (many reports were on using various methods for locating the MC).

I saw that one report indicated that there was a need to restimulate the site after 6 mos but that this was considered to be easily achieved because the site was known. I suppose they could leave the electrodes in-place and stimulate the site periodically as needed.

The report by Saitoh etal, said it expanded its results to thalamic, SCI, and phantom limb.

This would be wonderful if more research bears out that it causes relief for central pain in SCI and is a viable method.

Dr. Young please comment what you think of these reports and how can we encourage them to do more testing

Joe B

[David Berg]

I did a little more research on motor cortex stimulation. It has been around for awhile, it seems, and bears more research. One article I found is down right spooky. I won't post the whole thing here, but it's located at http://www.neurosurgery.org/journals/online_j/may99/6-5-p2.html

The jist of it is that one woman in Italy had motor cortex stimulation and then experienced phantom limb pain, for a false third arm. Just what we need, central pain in body parts that don't really exist! Apparently this woman is the only reported case with this side effect, but it serves as an example of how badly things can go wrong. IMHO, that's just downright spooky.

Joe B, if you try to leave the electrodes in place, the problem is that I don't think there's any structure available to anchor the electrode in place. (am I wrong on this Wise?) That can be a problem, since I've heard of other treatments where electrodes cannot be anchored and they tend to "drift" within several months, meaning that you need additional deep brain surgery or else you leave the electrodes to wander about. Gray matter is very soft and doesn't have what it takes to hold an electrode in place without some other means of support.

David Berg

[Wise Young]

Joe B,

The field is still in somewhat of a disarray concerning the best place to stimulate the brain to relieve central pain after stroke and other conditions. Cortical stimulation is often used because it is easily accessible and relatively non-invasive. Deep brain stimulation has also been used (i.e. in the thalamus and hypothalamus). In the old days (i.e. 20 years or more ago), they use to use cerebellar stimulation.

Part of the rationale for using brain stimulation and particularly cortical stimulation is the abundance of inhibitory connections between different parts of the brain. In people with neuropathic pain, several areas in the brain and thalamus tend to light up on scans of brain activity. The goal of the cortical stimulation is to find the place in the cortex that inhibits these areas and hopefully reduce pain. There is no question that stimulation does work in some people. The question is where to stimulate, how to make it more consistent, and what conditions it is most effective for. By the way, spinal cord stimulation is in much the same state. There is substantial evidence that spinal cord stimulation can reduce neuropathic pain in some people but the precise locations of stimulation are not well established (or perhaps not even estabishable because different people may require different stimulation locations and paradigms).

David, I don't think that there is any problem with the anchoring of electrodes in deep brain structures. The gray matter is not that soft. It is possible to do deep brain stimulation for long periods of time. The only problem of course is that one has to insert the electrode deep and the electrode itself does damage the brain through the insertion path. In the coming years, this is likely to change because new generations of electrodes will be available, including wireless ones.


Wise.

[David Berg]

Wise,

Thank you for your response. Most of my statement on the problem of electrodes becoming displaced comes from speaking to a patient who traveled to Toronto to see Dr. Ron Tasker, one of the premeir clinicians in the area of central pain. He told this patient that he was not a good candidate for electrodes for pain management due to the fact that his pain covers his entire body that he would require quite a few electrodes to be placed and that they have a tendency to move if not anchored, often within a matter of 6 months or so. For patients that would need electrodes in areas that do not offer a good way to anchor them, he recommended that they were really only appropriate for terminal patients, such as patients with central pain from advanced cancer.

That said, I've never had the opportunity to handle gray matter myself and I can only go from descriptions from others about its nature, which is where I came up with the statement that it's so soft.

I'm not stating all of this as any sort of counter anything you said in any way, only to pass along how I came by my information. As always, I value your wisdom and experience.

I will mention that, at least in regards to TENS treatment for central pain patients, that it should be tried with caution. One central pain patient that I know gave TENS a try only to find that it dramatically increased his pain in some areas of his body for 2 or 3 months. This sort of hazard makes it especially difficult to search for an effective way to manage pain.

David Berg

[craig]

Thank you all, W. Young , David, and Joe B for information a little more understanding.
craig