Ronald R. Tasker

Spinal cord stimulation for nonspecific limb pain versus neuropathic pain and spontaneous versus evoked pain.

OBJECTIVE To compare the outcome of spinal cord stimulation (SCS) in patients with nonspecific limb pain versus patients with neuropathic pain syndromes and in patients with spontaneous versus evoked pain. METHODS A retrospective review of 122 patients accepted for treatment with SCS between January 1990 and December 1998 was conducted. All patients first underwent a trial of SCS with a monopolar epidural electrode. Seventy-four patients had a successful trial and underwent permanent implantation of the monopolar electrode used for the trial (19 patients), or a quadripolar electrode (53 patients), or a Resume quadripolar electrode via laminotomy (2 patients). RESULTS Of the 74 patients, 60.7% underwent implantation of a permanent device and were followed for an average of 3.9 years (range, 0.3–9 yr). Early failure (within 1 yr) occurred in 20.3% of patients, and late failure (after 1 yr) occurred in 33.8% of patients. Overall, 45.9% of patients were still receiving SCS at latest follow-up. Successful SCS (>50% reduction in pain for 1 yr) occurred in 83.3% of patients with nonspecific leg pain, 89.5% of patients with limb pain associated with root injury, and 73.9% of patients with nerve neuropathic pain. SCS was less effective for the control of allodynia or hyperpathia than for spontaneous pain associated with neuropathic pain syndromes. Third-party involvement did not influence outcome. There was a lesser incidence of surgical revisions when quadripolar leads were used than with monopolar electrodes. CONCLUSION SCS is as effective for treating nonspecific limb pain as it is for treating neuropathic pain, including limb pain associated with root damage.

Microelectrode-guided Thalamotomy for Parkinson's Disease

OBJECTIVEnTo describe the outcomes in our first 40 microelectrode-guided thalamotomies for parkinsonian tremor.nnnMETHODSnTwenty-four left-sided and 16 right-sided thalamotomies were performed between October 1984 and January 1996; the mean follow-up period was 35.8 months (range, 1-152 mo). The results were evaluated retrospectively and semiquantitatively by a disinterested observer (MNL) and correlated with the quality of the microelectrode recording and the number and size of radiofrequency lesions made. The first 20 and second 20 procedures were evaluated separately.nnnRESULTSnAt the last follow-up, the Unified Parkinsons Disease Rating Scale showed no or virtually no tremor in the upper limb in 75% of patients or in the lower limb in 73% of patients. No significant persistent complications were found. These results were achieved at the expense of having to repeat the procedure on 11 sides (in 5 because of technical problems and in 6 for no obvious reason). Total or nearly total abolition of tremor occurred after the first procedure in 40% of the first 20 operations and in 65% of the second 20. Eight of the first 20 procedures and 2 of the second 20 failed for technical reasons. Lesions were made larger in the second 20 procedures than in the first 20. With the use of an electrode with a 1.1 x 3-mm bare tip for 60 seconds, it seems that lesions had to be created at 60 degrees C or more to produce a successful result.nnnCONCLUSIONnThalamotomy with microelectrode recording is an effective procedure with which to treat tremor in patients with Parkinsons disease and may involve fewer complications than conventional techniques. The procedure appears to involve a learning curve.

Brain Targets for Pain Control

A variety of brain sites have been targeted for surgical treatment of intractable pain. Both ablative and chronic stimulation procedures have been reported to attenuate such pain. These targets include the thalamus and its projections, the periventricular gray, the cingulate cortex and the motor cortex. An overview of these procedures and their efficacy is provided.

Microelectrode findings in the thalamus in chronic pain and other conditions

Functional neurosurgery usually requires physiological corroboration of the target site, particularly by eliciting characteristic responses to stimulation, or else by microelectrode recording of single cell responses to appropriate stimuli. Understanding pain physiology with both strategies has proven elusive, particularly microelectrode recording in response to noxious or thermal stimuli. The limited experience with stimulation and recording in pain pathways of the brain will be reviewed as well as the apparently pathophysiological observations made in certain patients with neuropathic pain.

The Effects of Pallidotomy on Parkinson’s Disease: Study Design and Assessment Techniques

Lesions of the internal segment of the globus pallidus are increasingly being utilized in the surgical treatment of advanced Parkinsons disease, yet studies to demonstrate the safety and efficacy of these procedures are only now being completed. The importance of procedural variations between centres in the outcome of pallidotomy is not yet known. In order to compare accurately results between centres, carefully designed, prospective studies are needed. The authors utilized blinded, randomly evaluated videotaped examinations of pre- and post-operative patients undergoing microelectrode-guided GPi pallidotomy. Their results demonstrate significant effects on contralateral akinesia and tremor in the off state, and striking attenuation of levodopa-induced dyskinesias in the on state. More modest effects on postural stability and gait disturbance were seen only in non-blinded evaluations. This type of study design should enable many of the outstanding issues related to pallidotomy indications, procedures and outcomes to be addressed.

Sleeping Cells in the Human Thalamus

Neurons in the lateral thalamus of a patient undergoing stereotactic surgery were found to fire in a characteristic bursting pattern only when the patient was asleep. These novel observations are consistent with animal studies in which the tonic firing pattern of thalamic neurons during wakefulness changes to a bursting pattern during slow-wave sleep.

History of lesioning for pain.

The history of open and subsequently stereotactic brain lesions for the relief of pain is traced. Important steps included recognition of the importance of the non-specific pain pathways and the differential effects of lesioning on nociceptive pain and on different elements of neuropathic pain. Although the advent of morphine infusion and deep brain stimulation has greatly eroded the number of destructive lesions made, new technical and conceptual advances must be carefully evaluated.