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Robert J. Coffey and Andres M. Lozano

Object

Neurostimulation to treat chronic pain includes approved and investigational therapies directed at the spinal cord, thalamus, periaqueductal or periventricular gray matter, motor cortex, and peripheral nerves. Persistent pain after surgery and work-related or neural injuries are common indications for such treatments. In light of the risks, efforts, costs, and expectations associated with neurostimulation therapies, a careful reexamination of the methods used to gather evidence for this treatment’s long-term efficacy is in order.

Methods

The authors combed English-language publications to determine the nature of the evidence supporting the efficacy of neurostimulation therapies for chronic noncancer pain. To formulate recommendations for the design of future studies, the results of their analysis were compared with established guidelines for the evaluation of medical evidence.

Evidence supporting the efficacy of neurostimulation has been collected predominantly from retrospective series or from prospective studies whose design or methods of analysis make them subject to limited interpretation. To date, there has been no successful clinical study focused on establishing the efficacy of neurostimulation for pain and incorporating sufficient numbers of participants, matched control groups, sham stimulation, randomization, prospectively defined end points, and methods for controlling experimental bias. Currently available data provide little support for the common practices of psychological or pharmacological screening or trial stimulation to predict and/or improve long-term results.

Conclusions

These findings do not diminish the value of previous investigations or positive patient experiences and do not mean that the treatments are ineffective; rather, they reveal that new data are required to answer the questions raised in and by previous study data. Future analyses of emerging neurostimulation modalities for pain should, whenever feasible, require unambiguous diagnoses as an entry criterion and should involve the use of randomization, parallel control groups that receive sham stimulation, and blinding of patients, investigators, and device programmers. Given the chronicity of patient symptoms and stimulation therapies, efficacy should be studied for 1 year or longer after device implantation. Meticulous study methods are especially important to evaluate new therapies like motor cortex and occipital nerve stimulation.

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Kim J. Burchiel

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Robert J. Coffey, Terrence L. Cascino and Edward G. Shaw

✓ Hemangiopericytomas of the meninges, classified previously as angioblastic meningiomas, have a propensity to recur either locally or at distant sites within the nervous system after surgical resection. Visceral metastases also develop much more commonly in these lesions than in other types of histologically benign meningiomas. The radiosurgical gamma knife was used to treat five patients with 11 meningeal hemangiopericytomas (seven new, two recurrent, and two residual tumors) after surgical resection of an initially solitary intracranial lesion. Three patients had undergone multiple craniotomies and radiation therapy before referral, and two patients underwent a second radiosurgical procedure for lesions that appeared between 5 and 13 months after the first treatment session. Dramatic tumor shrinkage occurred in most patients within 6 to 10 months after treatment. The only treatment-related morbidity in this series was a partial visual-field defect in one patient with a large falx-tentorial junction hemangiopericytoma who had previously undergone radiation therapy. Radiosurgery appears to cause dramatic early shrinkage of small and medium-sized intracranial hemangiopericytomas that have recurred or developed after previous surgery and/or radiation therapy.

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Akio Morita, Robert J. Coffey, Robert L. Foote, David Schiff and Deborah Gorman

Object. In this study the authors sought to determine the neurological risks and potential clinical benefits of gamma knife radiosurgery for skull base meningiomas.

Methods. A consecutive series of 88 patients harboring skull base meningiomas were treated between 1990 and 1996 by using the Leksell gamma knife in a prospective clinical study that included a strict dose—volume protocol. Forty-nine patients had previously undergone surgery, and six had received external-beam radiotherapy. The median treatment volume was 10 cm3, and the median dose to the tumor margin was 16 Gy. The radiosurgical dosage to the optic nerve, the cavernous sinus, and Meckel's cave was calculated and correlated with clinical outcome. The median patient follow-up time was 35 months (range 12–83 months).

Two tumors (2.3%) progressed after radiosurgery; the progression-free 5-year survival rate was 95%. At last follow-up review, 60 (68%) tumors were smaller and 26 (29.5%) remained unchanged. Clinical improvement (in vision, trigeminal pain, or other cranial nerve symptoms) occurred in 15 patients. Functioning optic nerves received a median dose of 10 Gy (range 1–16 Gy), and no treatment-induced visual loss occurred. Among nine patients with new trigeminal neuropathy, six received doses of more than 19 Gy to Meckel's cave.

Conclusions. Gamma knife radiosurgery appeared to be an effective method to control the growth of most skull base meningiomas in this intermediate-term study. The risk of trigeminal neuropathy seemed to be associated with doses of more than 19 Gy, and the optic apparatus appeared to tolerate doses greater than 10 Gy. Considering the risks to cranial nerves associated with open surgery for comparable tumors, the authors believe that gamma knife radiosurgery is a useful method for the management of properly selected recurrent, residual, or newly diagnosed skull base meningiomas.

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Michael J. Link, Robert J. Coffey, Douglas A. Nichols and Deborah A. Gorman

✓ Over the past 5 years 29 patients with dural arteriovenous fistulas (AVFs) were treated by the authors using the Leksell radiosurgical gamma knife unit. Within 2 days after radiosurgery, 17 patients with AVFs that exhibited retrograde pial or cortical venous drainage (12 patients) and/or produced intractable bruit (eight patients) underwent particulate embolization of external carotid feeding vessels. The rationale for this treatment strategy was that radiosurgery was expected to cause obliteration of most fistulas after 12 to 36 months. In patients with bruit, ocular symptoms, or in those at risk for hemorrhage, treatment with embolization after radiosurgery kept the fistulas angiographically visible for radiosurgical targeting yet offered palliation of symptoms and temporary, partial protection from hemorrhage during the latency period. In 12 patients, preobliteration embolization immediately reduced (10 patients) or eliminated (two patients) retrograde pial venous drainage. To date, no lesion has hemorrhaged after treatment. Angiography 1 to 3 years posttreatment in 18 patients showed total obliteration of 13 fistulas (72%) and partial obliteration of five (28%). Radiosurgery, followed by embolization when retrograde pial venous drainage, intractable bruit, and/or major external carotid artery supply is present, appears to be a promising treatment for selected patients with symptomatic dural AVFs.

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Robert J. Coffey