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W J Levy

Publications and source records attributed to W J Levy.

At least 55 records · Page 3Linked to original sources
PubMed1987

Clinical experience with motor and cerebellar evoked potential monitoring.

We are reporting 98 cases of motor evoked potential (MEP) monitoring performed between 1982 and 1986. These were divided into supratentorial, posterior fossa, and spinal cord categories. We observed in this sample that the peripheral nerve or electromyographic response was substantially more sensitive than the spinal cord response to injury and hypotension during operation and was often present bilaterally. Reversible weakening or loss of the peripheral nerve response was not associated with a deficit. However, weakening of the peripheral nerve response without recovery could warn of a motor defect after operation. The spinal cord responses can change so little in amplitude and latency with injury conditions that their reliable use during operation without accompanying peripheral nerve and muscle response monitoring may be compromised, especially in view of the often difficult recording environment in the operating room. With spinal cord monitoring, the MEP seemed closely correlated with the stresses that we imposed on the cord, as well as with subsequent clinical outcome. In posterior fossa cases, we observed sensitivity of the MEP to manipulation of the nervous system and reliable indication of the outcome in the cases monitored. Supratentorial cases present a more complex environment for monitoring; a potential pitfall is to stimulate an area that produces responses in the peripheral nerves and spinal cord, but that is not being compromised by the injury process. Alternatively, stimulating too large an area of cortex or stimulating with too high a current, which penetrates to white matter below the gray matter, may not show an injury. Although we did not encounter cases where permanent deficits were missed by the motor evoked potential, we were concerned by the appearance of temporary deficits. These may be related to technical limitations of our methods and indicate that monitoring of the supratentorial process requires substantial methodological advance for high reliability. Modulation of the MEP by prior somatosensory evoked potential stimulation seems useful and promising. Cerebellar evoked potential responses were present in humans and were sensitive to injury. Overall, this test is promising.

Animals↗
PubMed1986

Power spectrum correlates of changes in consciousness during anesthetic induction with enflurane.

In order to correlate electroencephalogram (EEG) changes during anesthetic induction with level of consciousness, four-channel parasagittal EEG recordings were made during anesthetic induction with enflurane and enflurane-nitrous oxide in oxygen. The EEG was quantitated using power spectrum analysis. Significant EEG changes were identified during all anesthetic inductions; however, the frequency of occurrence of change was significant only during development of amnesia (15 of 20 subjects, P = 0.04). The nature of the EEG changes at this time was agent-specific (P less than 0.05 by chi-square), with high-frequency changes evident in the enflurane group and shifts in amplitude in the 8-12 Hz activity predominating in the nitrous oxide-enflurane group. Anterior dominance could not be documented as a correlate of amnesia or unresponsiveness. The identification of such EEG changes may be valuable in assessing anesthetic depth, but other effects, such as the response of the EEG to surgical stimulation, must be determined before the results are clinically applicable.

Amnesia↗
PubMed1986

Remission of acanthosis nigricans, hypertrichosis, and Hashimoto's thyroiditis with thyroxine replacement.

Hypothyroidism is not commonly associated with acanthosis nigricans (AN). We examined a 13-year-old girl with AN, hypertrichosis, and Hashimoto's thyroiditis. Overt biochemical hypothyroidism, thyroid enlargement, and positive titers of antimicrosomal and antithyroglobulin antibodies confirmed Hashimoto's thyroiditis. Both AN and hypertrichosis resolved with thyroid hormone replacement. There was no evidence of insulin resistance, polycystic ovarian disease, lipoatrophy, or other endocrine dysfunction, or of malignancy. In two patients from the literature with AN and hypothyroidism, AN was attributed to associated thyroid carcinoma or insulin resistance, rather than coexisting hypothyroidism. Since the skin lesions improved with thyroid hormone therapy in those two patients and in ours, hypothyroidism appears to be directly involved in the pathogenesis of AN.

Acanthosis Nigricans↗
PubMed1986

Spinal neurofibromas: a report of 66 cases and a comparison with meningiomas.

A series of 66 spinal cord neurofibromas was analyzed for history, signs, surgical approach, and outcome. The tumors presented primarily with sensory symptoms. Plain films were abnormal in 1/2 of cases and 1/2 had a complete block. They were primarily intradural, and primarily thoracic. A conservative exam system was used for follow-up and 85% with pain had complete relief; 50% with motor loss had normal motor function, and 88% had normal sensation who had prior sensory loss. In comparison to meningiomas, the principal differences were that neurofibromas had an even sex distribution, a lower incidence of cord signs and symptoms, more frequent findings on plain x-rays, and higher cerebrospinal fluid protein. Surgical outcome was similar. Sacrifice of the involved root during removal usually did not produce a deficit. The series is compared with a similar series of meningiomas from the same institution over the same time period.

Adolescent↗
PubMed1986

Nonpyramidal motor activation produced by stimulation of the cerebellum, direct or transcranial: a cerebellar evoked potential.

There is a need to monitor the functional status of the motor pathways well enough to predict the state of that function during operations and in injured or diseased patients. We previously reported that a motor evoked potential (MEP) can be produced by direct or transcranial stimulation of the motor cortex in both cats and humans. This signal descends through both the dorsolateral and ventral spinal cord and is primarily localized in the pyramidal tracts, producing a peripheral nerve signal and an electromyogram (EMG) response. It is more sensitive to injury than the somatosensory evoked potential (SEP). We report here that one can stimulate the cerebellar cortex, either directly or transcranially, and produce a descending signal in the spinal cord that has different characteristics from the MEP. The cerebellar evoked potential (CEP), located in the dorsolateral and the ventral cord, has an earlier latency and a faster conduction velocity than the MEP. It is predominantly ipsilateral with some contralateral components and also produces EMG responses. In the peripheral nerves, the CEP often produces a pattern of several waves that is different from the one or two predominant contralateral waves of the MEP. The CEP is not diminished by pyramidotomy. It arises from two sites on the cerebellar cortex, medial and lateral. The pathways activated may be the vestibulospinal, rubrospinal, reticulospinal, and fastigiospinal systems. This test seems to offer a monitor of selected motor pathways in the spinal cord largely separate from and complementary to the MEP. The ventral pathways activated probably include those demonstrated to be most essential to basic ambulation after spinal cord injury in primates. Also of importance, one type of evoked potential can facilitate another, which provides additional diagnostic tests. The CEP should be of investigative and clinical value.

Animals↗
PubMed1985

A method for in vitro enzymatic dissociation of nerve roots and peripheral nerves from adult mammals.

Preparations yielding a high percentage of undamaged axons from fresh peripheral nerve or nerve root were made using an enzymatic dissociation regimen. The nerve was placed in a temperature-controlled chamber mounted over an inverted phase-contrast microscope. An oxygenated solution (Brimijoins) or modified Hank's solution was pumped through the chamber, first in a calcium-free form and then containing enzymes. The enzymes for dissociation were collagenase and trypsin, alternated. Enzymatic dissociation of the epineurium, perineurium and extracellular matrix was achieved. We supplemented the gentle agitation of a 10-roller peristaltic pump by periodically raising and lowering the fluid level in the chamber to provide a controlled mechanical agitation that promoted dissociation. A large percentage of the axons can be dissociated from the nerve, varying from approximately one-quarter to occasional complete dissociation. Action potentials were still conducted through dissociated axons, and axon transport was also still present, as documented by direct visualization using an AVEC-DIC type of microscope system. The axons had a better morphological appearance and displayed better transport than comparison preparations prepared by the usual mechanical teasing method, in our hands. The enzymatic method allows study of axons in an adult or developing mammal with regard to their electrical conduction and axon transport mechanisms. It should help to avoid a selection process for more hardy axons which may be imposed by traditional mechanical teasing methods. Mechanical stress was observed to cause widened Schmidt-Lanterman clefts, widened nodes, myelin bubbles, and other abnormal morphology as evidence of damage.

Animals↗
PubMed1985

Comparison of laser and radiofrequency dorsal root entry zone lesions in cats.

Dorsal root entry zone lesions are effective in the control of intractable pain in several types of spinal cord injuries. Traditionally, these lesions have been made with the radiofrequency technique. This is effective, but has the drawback of being laborious, and there is a significant incidence of permanent weakness. We have evaluated the carbon dioxide laser, hoping that it would be both faster and more controlled, thereby offering the chance to lower the complication rate. In comparing a parallel series of radiofrequency and laser dorsal root entry zone lesions along the cat's spinal cord, we observed that the radiofrequency lesion was larger. In addition, it had 3 times more variability in its size than the laser lesion. We attribute this in part to the nature of the laser in making a very precise and reproducible lesion. Second, the extremely brief pulse of the laser, a fraction of a second, means that movement of the spinal cord from respiration and heartbeat and movement of the surgical instrument from the surgeon's hand become far less important in inducing lesion variability. We also studied for 2 months a series of chronic cats; there were no complications due to the laser. This work suggests that the laser is a useful instrument for dorsal root entry zone lesions, but requires more precise aiming and focusing.

Animals↗
PubMed1985

Model for the study of individual mammalian axons in vivo, with anatomical continuity and function maintained.

Methods for the study of axons involve whole nerve preparations, teased preparations of axons that are excised from their proximal and distal connections, and tissue culture models. As a complement to these, it would be advantageous to study separated, isolated axons in vivo, still in continuity with the end organ distally and the spinal cord central nervous system neuron proximally. This would allow the study of axon function, normal or pathological, in a close relationship to its biological environment. To achieve this, we have passed the surgically isolated sciatic nerve of a rat through a chamber specially designed for enzymatic dissociation. This was based on principles derived from a prior in vitro method for dissociating nerve into axons. The chamber has controlled temperature and flow and is on an inverted microscope stage, allowing observation of the process. We perfused the chamber with a calcium-free solution followed by a series of enzymes: collagenase, trypsin, and hyaluronidase. This dissociates that part of the extracellular matrix external to the Schwann cells, leaving free, myelinated axons with their Schwann cells. In this acute preparation, the axons continue to conduct action potentials for at least 8 hours. Furthermore, an in vitro study of the axon after the in vivo dissociation demonstrated that axonal transport was maintained in over 90% of the axons, directly visualized on an AVEC-DIC type of microscope system. Properties of axonal transport or active spike propagation can thus be studied individually in an in vivo axon preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Unusual problems for the physician in managing a hospital patient who received a malicious insulin overdose.

A patient recovering normally from a biopsy and subtotal removal of a malignant brain tumor became severely hypoglycemic on the ward and died. The differential diagnosis eliminated disease as a possible cause, and medication error on the floor was also ruled out. Deliberate administration of a massive dose of insulin intravenously seemed to be the only alternative. A careful investigation supported the likelihood of a criminal act. The patient's wife came under suspicion and was subsequently arrested, charged with murder, and convicted. This sequence of events created three problems that fell outside of our normal professional training and experience as physicians. First, we were slow to suspect foul play in our search for an unusual cause. Second, the steps taken to protect the patient against further risk without denying reasonable rights to family or arousing the suspect's suspicions needed strengthening. Third, even though the occurrence of these events in a hospital allowed an unusual degree of evidence documenting the allegations to be accumulated, key parts of the evidence could not be used. The routine hospital handling of laboratory tests critical to support of the accusations was not sufficient to meet the demands of the legal system, which has its own criteria. We discuss the issues in managing these problems.

Blood Glucose↗
PubMed1984

Quantitative analysis of EEG changes during hypothermia.

Power spectrum analysis of 4-channel EEGs was performed during cooling and rewarming using cardiopulmonary bypass. During rewarming, linear correlations of temperature with the total power and with peak power frequency of the high-frequency band were observed in a significant number of cases (85%, P less than 0.0001 and 76%, P less than 0.002, respectively). The magnitude of these changes were 1,215 microV2/degrees C (+/- 150 [SEM] ) and 0.39 Hz/degrees C (+/- 0.04 [SEM] ). Two other descriptors of the EEG power spectrum (the spectral edge and average frequencies) did not correlate with the temperature changes in a significant number of cases. Changes during cooling followed a similar trend but were more variable, presumably because of other physiologic changes associated with the start of bypass. Knowledge of the relationship of the EEG to temperature should permit distinguishing EEG changes secondary to hypothermia from those caused by acute hypoxia.

Brain↗
PubMed1984

Intraoperative EEG patterns: implications for EEG monitoring.

Univariate descriptors such as the mean frequency and spectral edge frequency have been proposed for intraoperative representation of the EEG. Such univariate descriptors of the EEG are accurate only when the EEG behaves as a unimodal distribution of frequencies that change slowly with time. EEGs were recorded from 64 patients undergoing anesthetic inductions and 30 patients undergoing cardiopulmonary bypass to determine the characteristics of the observed distribution of frequencies. Multimodal EEG activity was observed in 64% of these cases, including 83% of those patients undergoing cardiopulmonary bypass. The differences between the two peaks averaged 7.6 Hz, and the average ratio of the power of the peaks to the intervening valley was 2.5:1 and 1.9:1. Calculations of mean frequency and spectral edge frequency failed to adequately reflect the complexity of the EEG in these cases. Burst-suppression activity was observed in 26% of cases during cardiopulmonary bypass, and averaging over time destroyed the characteristic pattern. Thus, univariate descriptors of the EEG appear inadequate to describe the behavior of EEG during anesthesia in a large percentage of cases.

Alpha Rhythm↗
PubMed1984

Curved biopsy needle for stereotactic surgery: a technical note.

Needle brain biopsy and aspiration is an important technique for the diagnosis of tumors and for the evacuation of fluid collections. Current biopsy methods use a straight needle, which has the disadvantage of requiring multiple passes through the overlying brain to obtain multiple biopsies. Furthermore, a straight needle does not give optimal samples of tumor for diagnosis because the needle passes through the viable rim of the tumor instead of along it. We are reporting a curved plastic biopsy needle suitable for computed tomography-guided biopsy. It remains inside an outer guide catheter that holds it straight until it reaches the edge of the tissue to be biopsied. At this point, the needle is advanced beyond the guide catheter and obtains the biopsy sample by passing around the edge of a tumor. This can in principle produce an improvement in diagnostic yield. Furthermore, multiple biopsies of the tumor from a single guide catheter position are possible. The surgeon rotates the curved needle within its guide catheter to redirect it before the needle emerges, and a different biopsy is then obtained without reinsertion. This avoids multiple punctures of the overlying uninvolved tissue. We are reporting the technique and beginning an evaluation of it.

Biopsy, Needle↗
PubMed1984

Motor evoked potentials from transcranial stimulation of the motor cortex in cats.

Electrical testing of central nervous system pathways is assuming increasing importance in clinical medicine. However, there is no direct monitor of the motor system. We previously reported using a motor evoked potential created by direct excitation of the spinal cord, placing a stimulating electrode over the corticospinal tract area. To produce a less invasive test, we now use direct transcranial stimulation of the motor cortex through the scalp or direct stimulation of the motor cortex itself during operation. A descending signal can be recorded over the spinal cord and in the peripheral nerves where no retrograde sensory signals should be able to descend. This motor cortex stimulation produces contralateral limb movements and selective activation of the peripheral nerves of a limb. The characteristics of this signal are similar to those described in the neurophysiological literature for a descending motor signal. With a depth electrode, it was found that the signal was strongest in the spinal cord near the corticospinal tracts and in the anterior horn cell area. A set of lesioning studies showed that most of the signal travels in the area of the corticospinal tract, with some traveling in the ventral portion of the spinal cord, perhaps in the anterior corticospinal tract. Section of the pyramid essentially abolishes the signal, but lesioning of the red nucleus does not. This test offers an electrical assessment of the motor system that can be useful in experimental work on spinal cord and brain function. It has potential clinical applicability in humans.

Animals↗
PubMed1984

Motor evoked potentials from transcranial stimulation of the motor cortex in humans.

Electrical monitoring of the motor system offers the potential for the detection of injury, the diagnosis of disease, the evaluation of treatment, and the prediction of recovery from damage. Existing evoked potentials monitor one or another sensory modality, but no generally usable motor monitor exists. We have reported a motor evoked potential using direct stimulation of the spinal cord over the motor tracts in cats and in humans. To achieve a less invasive monitor, we used transcranial stimulation over the motor cortex in the cat, thus stimulating the motor cortex. We report here the initial application of this method to humans. A plate electrode over the motor cortex on the scalp and a second electrode on the palate direct a mild current through the motor cortex which will activate the motor pathways. This signal can be recorded over the spinal cord. It can elicit contralateral peripheral nerve and electromyographic signals in the limbs or movements when the appropriate stimulation parameters are used. In clinical use to date, this has been more reliable than the somatosensory evoked potential in predicting motor function in patients where the two tests differed. It offers a number of possibilities for the development of valuable brain and spinal cord monitoring techniques, but requires further animal studies and clinical experience. Studies to date have not demonstrated adverse effects, but evaluation is continuing.

Adult↗