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Biomedical subjects

R B North

Publications and source records attributed to R B North.

At least 19 recordsLinked to original sources
PubMed1997

Artificial neural networks: application to electrical stimulation of the human nervous system.

Artificial neural networks are used increasingly in applications such as graphic pattern recognition, which are difficult to address with conventional statistical methods. In the management of chronic pain, graphic methods are used routinely; patients describe their patterns of pain using "pain drawings." The authors have previously reported an automated, computerized pain drawing methodology, which has been used by patients with implanted spinal cord stimulators to represent a technical goal of the procedure, the overlap of pain by stimulation paresthesias. Standard linear discriminant statistical methods have shown associations between stimulation parameters and electrode positions as independent variables and technical outcome and relief of pain as dependent variables. The authors have applied artificial neural networks to the problem of optimizing implanted stimulator adjustment. A data set of 3000 electrode combinations obtained in 41 patients was used to develop a linear discriminant statistical model on a mainframe computer and to train artificial neural networks on a personal computer. The performance of these two systems on a new data set obtained in 10 patients was compared with that of human "experts." The best neural network model was marginally better than the linear discriminant model; the variance in patient ratings was predicted by these models to a degree that the human experts were unable to predict. The authors anticipate expanding the role of these models and incorporating them into expert systems for clinical use.

Journal Article↗
PubMed1997

Spinal cord stimulation with percutaneous and plate electrodes: side effects and quantitative comparisons.

Spinal cord stimulation is limited by the uncomfortable side effects experienced by the patient as the amplitude of stimulation is increased. These side effects include local segmental paresthesias or motor responses, which are objectively demonstrable as frequency-following muscle contractions, attributable to dorsal root stimulation. The authors present evidence for another mechanism of stimulation-evoked discomfort, namely recruitment of small fibers in ligamentum flavum, which occurs when electrodes are inserted percutaneously and their contacts are exposed circumferentially; this does not occur with plate electrodes with insulated dorsal surfaces. In a consecutive series of 79 patients with postsurgical lumbar pain syndromes, percutaneous four-contact electrodes were tested at levels from T-8 through T-12. At one or more levels, 46% of patients described paravertebral, nonradiating discomfort, unaccompanied by frequency-following muscle contractions. This was observed most commonly at the T-8 and T-9 levels. The effect was ameliorated in some cases by using multiple cathodes in parallel, which reduced the current density at individual contacts. In 10 of these patients, this side effect interfered with an otherwise successful trial to such a degree that an insulated plate electrode was selected for permanent implantation at the same level as the percutaneous electrode. This eliminated the uncomfortable side effect completely in all patients. Intraoperative testing with the insulated plate electrode inverted (that is, contacts dorsal) reproduced the side effect in the majority of patients, indicating that structures dorsal to the electrode, such as fibers in ligamentum flavum, mediate the effect. Postoperative testing by computerized techniques demonstrated improved coverage of pain by stimulation paresthesias, with lower stimulation power requirements, using the insulated plate electrode. This technical limitation of percutaneous spinal cord stimulation electrodes, which may confound treatment if unrecognized, has been found to have a straightforward solution which indicates the underlying mechanism.

Journal Article↗
PubMed1997

Cost-effectiveness analysis of spinal cord stimulation in treatment of failed back surgery syndrome.

This article presents an analysis of the medical costs of spinal cord stimulation (SCS) therapy in the treatment of patients with failed back surgery syndrome (FBSS). We compared the medical costs of SCS therapy with an alternative regimen of surgeries and other interventions. Externally powered (external) and fully internalized (internal) SCS systems were considered separately. Clinical management models of each of the therapy alternatives were derived from the clinical literature, retrospective data sets, expert opinion, and published diagnostic and therapy protocols. No value was placed on pain relief or improvements in the quality of life that successful SCS therapy can generate. We found that by reducing the demand for medical care by FBSS patients, SCS therapy can lower medical costs. On average, given current screening and efficacy rates, SCS therapy pays for itself within 5.5 years. For those patients for whom SCS therapy is clinically efficacious, the therapy pays for itself within 2.1 years.

Back Pain↗
PubMed1997

Primary intracerebral small-cell osteosarcoma in an adolescent girl: report of a case.

A young patient surviving four years after treatment for primary intracerebral small-cell osteosarcoma is reported. This 16-year-old girl presented with headaches, visual disturbance, and papilledema and was found to have a large, heavily calcified mass in the left parietal lobe. A gross total resection of the tumor was performed and pathologic analysis revealed a small-cell osteosarcoma. Thoracic computerized tomography (CT) scans and a complete bone scan showed no other lesions. The patient received adjuvant chemotherapy and radiotherapy. She continues to do well with no evidence of metastases or local recurrence 4 years after her initial presentation. The clinical, radiographic, surgical, pathologic, and immunohistochemical features of this case, along with therapeutic interventions and outcome, are presented.

Adolescent↗
PubMed1996

Pneumosinus dilatans: a sign of intracranial meningioma.

BACKGROUND: Pneumosinus dilatans affecting the sphenoid and posterior ethmoid sinuses has been reported in association with spheno-orbital meningiomas and is believed by some authors be a sign of an adjacent meningioma. METHODS: We report the case of a 57-year-old man who developed progressive neurologic signs and symptoms consistent with a frontal lobe lesion. Neuroimaging studies revealed a large partially cystic mass at the base of the anterior cranial fossa that appeared to be invading the left frontal lobe and that was associated with pneumosinus dilatans of the adjacent left frontal sinus. RESULTS: Although the appearance of the mass by neuroimaging was thought to be most consistent with a malignant glioma, the lesion was found at craniotomy to be a benign meningothelial meningioma. CONCLUSIONS: Many previous cases of progressive optic neuropathy associated with pneumosinus dilatans affecting the sphenoid and posterior ethmoid sinuses have been found to be caused by adjacent optic nerve sheath meningiomas. This case provides further evidence that pneumosinus dilatans is a sign of intracranial meningioma.

Humans↗
PubMed1996

Prognostic value of psychological testing in patients undergoing spinal cord stimulation: a prospective study.

OBJECTIVE: Associations between psychological and physical states are understood to exist, and the development of standardized psychological tests has allowed quantitative evaluation of this relationship. We tested whether associations exist between psychological test instruments and patients selected for therapeutic trials of spinal cord stimulation (SCS) for chronic, intractable pain. METHODS: Fifty-eight patients selected for SCS were tested prospectively with a battery of standardized psychological tests: Minnesota Multiphasic Personality Inventory with Wiggins content scales, Symptom Check List-90, and Derogatis Affects Balance Scale. Associations between treatment outcomes and preoperative test scores and clinical variables were tested by univariate and multivariate statistical analyses, in which the dependent variables were as follows: 1) the outcome of a therapeutic trial of stimulation (whether the patient derived sufficient reported pain relief with a temporary electrode to proceed with a permanent implant), and 2) long-term outcome of treatment with the permanent implant, as determined by disinterested third-party interview. RESULTS: Significant associations (P < or = 0.01) were observed between the outcome of the therapeutic trial of stimulation and psychological test results; patients with low "anxiety" scores on the Derogatis Affects Balance Scale and with high "organic symptoms" scores on the Wiggins test were significantly more likely to proceed to permanent implants, as determined by multivariate statistical models. There was an elevation in the Minnesota Multiphasic Personality Inventory hypochondriasis scale in these patients by univariate (P = 0.02), but not by multivariate, models. The multivariate model also identified young age, reproduction of leg pain by straight leg raising, and bilateral leg pain as favorable prognostic factors. The only association with favorable long-term outcome of implantation of a permanent device, by univariate analysis, was an elevated "joy" score on the Derogatis Affects Balance Scale. Multivariate analysis revealed no statistically significant predictors of long-term outcome. CONCLUSION: Because our study population was selected on the basis of recognized prognostic factors and long clinical experience, it may not be possible to generalize our findings to the overall pain clinic referral population. In the subpopulation we have chosen for SCS trials, psychological testing is of modest value and explains little of the observed variance in outcome. We find little evidence for selecting patients for SCS on the basis of psychological testing. Because self-reported outcome measures may themselves reflect the patient's psychological state, these findings should be considered carefully, in overall clinical context. A prospective study with additional objective outcome measures is underway, which will address some of these issues.

Adaptation, Psychological↗
PubMed1995

Spinal cord stimulation versus reoperation for failed back surgery syndrome: a prospective, randomized study design.

Retrospectively reported results of spinal cord stimulation compare favorably with those of neurosurgical treatment alternatives for the treatment of failed back surgery syndrome, including reoperation and ablative procedures. There has been no direct prospective comparison, however, between SCS and other techniques for pain management. Therefore, we have designed a prospective, randomized comparison of spinal cord stimulation and reoperation in patients with persistent radicular pain, with and without low back pain, after lumbosacral spine surgery. Patients selected for reoperation by standard criteria are randomly assigned to initial treatment by one or the other technique. The primary outcome measure is the frequency of crossover to the alternative procedure, if the results of the first have been unsatisfactory after 6 months. Results for the first 27 patients reaching the 6-month crossover point show a statistically significant (p = 0.018) advantage for spinal cord stimulation over reoperation. Many other potentially important outcome measures will now be followed long-term as a larger overall study population accumulates.

Electric Stimulation Therapy↗
PubMed1995

Implantable pumps for drug delivery to the brain.

This article reviews the role of implantable pumps in the treatment of CNS tumors. Systemic administration of chemotherapeutic agents has been associated with various problems, including adverse systemic effects and decreased concentration of the drug at the target site. Continuous infusion of chemotherapeutic agents with implantable pumps have been used in an attempt to overcome these problems. Various different chemotherapeutic agents have been used for this purpose, and catheters have been placed in the intraspinal, intraventricular and intratumoral locations.

Alzheimer Disease↗
PubMed1995

Spinal cord stimulation for chronic pain.

Electrical stimulation of the spinal cord for the relief of pain was first reported in 1967. Since that time, there have been marked improvements in patient selection criteria, hardware, technology, and methods for implantation, which have resulted in substantial improvement in the overall results achieved with spinal cord stimulation.

Chronic Disease↗
PubMed1994

A prospective, randomized study of spinal cord stimulation versus reoperation for failed back surgery syndrome: initial results.

Spinal cord stimulation (SCS) has been reported to be effective treatment for the failed back surgery syndrome in a number of retrospective case series. Its retrospectively reported results compare favorably with those of neurosurgical treatment alternatives, such as reoperation and ablative procedures. There has been no direct prospective comparison, however, between SCS and other techniques for pain management. We have undertaken a prospective, randomized comparison of SCS and reoperation in patients with persistent radicular pain, with and without low back pain, following lumboscral spine surgery. Patients selected for reoperation by standard criteria have been randomly assigned to initial treatment by one or the other technique. The primary outcome measure is the frequency of crossover to the alternative procedure, if the results of the first have been unsatisfactory after 6 months. Results for the first 27 patients reaching the 6-month crossover point show a statistically significant (p = 0.018) advantage for SCS over reoperation. This is one of many potentially important outcome measures, which are to be followed long-term as a larger overall study population accrues.

Back Pain↗
PubMed1994

Consensus conference on the neurosurgical management of pain.

On the recommendation of the American Association of Neurological Surgeons Section on Pain, a satellite conference was organized for the 1993 annual meeting to work toward a consensus regarding the indications, expected outcomes, and potential complications of neurosurgical procedures for intractable pain. Twenty-two experts in the field attended this 2-day conference to consolidate our understanding of the role of neurosurgical procedures in pain management and to review critically the methodologies for clinical studies. With the support of the Section on Pain, this consensus development process will continue in order to refine the application and study of neurosurgical procedures for pain.

Algorithms↗
PubMed1993

Spinal cord stimulation for chronic, intractable pain: experience over two decades.

Over the past two decades, spinal cord stimulation devices and techniques have evolved from single-channel systems, with electrodes requiring laminectomy, into programmable "multichannel" systems with electrodes that may be placed percutaneously. We have reviewed our experience in 320 consecutive patients treated with these devices at our institution between 1972 and 1990. Technical details of treatment as well as patient characteristics have been assessed as predictors of clinical outcome and of hardware reliability by univariate and multivariate statistical methods. Current follow-up has been obtained at intervals from 2 to 20 years (mean, 7.1 yr) postoperatively on 205 patients. All clinical outcome measures have been based on disinterested third-party interview data--standard analog pain ratings, employment status, activities of daily living, and use of analgesics. At 7-year mean follow-up, 52% of the 171 patients who received permanent implants reported at least 50% continued pain relief. A majority had maintained improvements in activities of daily living and analgesic use. Analysis of hardware reliability for 298 permanent implants revealed significantly fewer clinical failures (P < 0.001) and technical failures (in particular, electrode migration and malposition, P = 0.025) as single-channel implants have evolved into programmable, multichannel devices. Our analysis of technical and clinical prognostic factors may be useful to the clinician in selecting patients for this procedure.

Adult↗
PubMed1992

Spinal cord stimulation evoked potentials during thoracoabdominal aortic aneurysm surgery.

Although monitoring of somatosensory evoked potentials elicited from stimulation of lower extremity peripheral nerves has been suggested as a method for assessing neural function during thoracoabdominal aortic aneurysm surgery, this technique has been reported to yield a large number of false positives. It was believed that direct stimulation of the spinal cord would eliminate some of the problems associated with peripheral evoked potentials. The present study compared in 18 patients the use of scalp recorded evoked potential following stimulation of either the posterior tibial nerve via percutaneous needles or the spinal cord via an epidural electrode previously placed fluoroscopically. In 10 patients in whom distal bypass or shunt was not used, peripheral evoked potentials totally disappeared within 5-30 min of aortic clamping. Spinal cord stimulation evoked potentials disappeared permanently in 2 patients shortly after aortic cross-clamping; 1 died shortly after the procedure, and the other awoke densely paraplegic and died the next day. When distal perfusion was maintained by shunt or bypass, the disappearance of both peripheral and spinal evoked potentials accurately predicted the neurologic outcome of 1 paralyzed patient. Loss of spinal cord stimulation evoked potentials was found to be correlated with adverse neurologic outcome. Over the period of aortic clamping a gradual decrease in mean amplitude (50% at 45 min [P less than 0.05]) and a 20% increase in mean latency time were observed. Maintenance of adequate distal perfusion may permit the use of peripheral evoked potentials in the assessment of spinal cord ischemia during aortic cross-clamping.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Patient-interactive, computer-controlled neurological stimulation system: clinical efficacy in spinal cord stimulator adjustment.

Over the past 20 years, continuing technical advances have rendered spinal cord stimulation an easily implemented low-morbidity technique for the management of chronic intractable pain in properly selected patients. Percutaneous methods for the insertion of arrays of multiple epidural electrodes, which are driven by noninvasively programmable "multichannel" implanted devices, have been among the most important of these technical improvements. The same implanted electronics may be used with peripheral nerve or intracerebral electrodes. If the capabilities of this new hardware are to be used to full advantage, a major investment of time and effort is required to adjust the system postoperatively for optimum effect. Ideally, these adjustments should be based upon psychophysical data, obtained in a manner that minimizes influences such as potential operator bias or stimulus presentation-order effects. These requirements have been met by the development of a computerized system designed for direct patient interaction and for greater ease of operation than the standard external devices used with these implants. The system has been tested clinically in 25 patients with spinal cord stimulation for pain. It rapidly tests the available electrode combinations and stimulus pulse parameters at a rate comparable to or greater than that of a skilled human operator using the standard device. It records detailed graphic data and patient analog ratings at varying thresholds and implements "pain drawing" methods with novel input and analytical techniques. This patient-interactive computerized system has proved to be safe and effective clinically. The time required by the average patient working with this system to adjust the stimulator is comparable to or less than the time required by the same patient working with a physician's assistant. Psychophysical data collected by the system may be correlated with clinical observations. Ongoing development will permit delivery of novel pulse sequences and protocols to assess the mechanisms by which stimulation affords relief from pain.

Electric Stimulation Therapy↗