Daniel M. Schwartz

Multimodality monitoring of transcranial electric motor and somatosensory-evoked potentials during surgical correction of spinal deformity in patients with cerebral palsy and other neuromuscular disorders.

Study Design. This prospective, descriptive study determined the reliability of transcranial electric motor and posterior tibial nerve somatosensory-evoked potentials in children with neuromuscular scoliosis. Objective. To assess the applicability of transcranial electric motor and posterior tibial nerve somatosensory-evoked potentials during surgical correction of neuromuscular scoliosis, particularly with cerebral palsy-related deformity. Summary of Background Data. During corrective spinal surgery for neuromuscular scoliosis, intraoperative multimodality spinal cord monitoring is recommended. There exist conflicting, retrospective studies regarding the reliability of spinal cord monitoring in patients with neuromuscular scoliosis. Methods. Transcranial electric motor potentials and posterior tibial nerve somatosensory-evoked potentials were monitored in all patients presenting for spinal fusion between 2000 and 2001. Anesthesia was standardized for all patients. Results. There were 68 patients subdivided into two subject groups. Group I consisted of 39 patients with neuromuscular scoliosis associated with cerebral palsy, and Group II consisted of 29 children with neuromuscular scoliosis due to a disease process other than cerebral palsy. Five of the 68 patients had significant amplitude changes in 1 or both monitoring methods during surgery relative to baseline. Of these, one had permanent neurologic deficit despite standard intervention. Somatosensory-evoked potentials were monitored successfully in 82% of the cerebral palsy and 86% of the noncerebral palsy patients. Transcranial electric motor-evoked potentials, on the other hand, were monitorable in 63% of patients with mild or moderate degrees of cerebral palsy and 39% of those with severe involvement. Eighty-six percent of those with noncerebral palsy-related neuromuscular scoliosis had recordable motor-evoked potentials at baseline. Conclusion. Both transcranial electric motor and posterior tibial nerve somatosensory-evoked potentials can be monitored reliably in most patients with neuromuscularscoliosis. Those with severe cerebral palsy present the greatest challenge to successful neurophysiologicmonitoring.

Neurophysiological Identification of Position-Induced Neurologic Injury During Anterior Cervical Spine Surgery

This study was a retrospective review of 3,806 patients who underwent anterior cervical spine surgery with multi-modality neurophysiological monitoring consisting of transcranial electric motor evoked potentials, somatosensory evoked potentials and spontaneous electromyography between 1999–2003. The objectives of this study were twofold: (1) to evaluate the role of transcranial electric motor evoked potential tceMEP and ulnar nerve somatosensory evoked potential (SSEP) monitoring for identifying impending position-related stretch brachial plexopathy, peripheral nerve entrapment/compression or spinal cord compression and (2) to estimate the point-prevalence of impending neurologic injury secondary to surgical positioning effects. Sixty-nine of 3,806 patients (1.8% showed intraoperative evidence of impending neurologic injury secondary to positioning, prompting interventional repositioning of the patient. The brachial plexus was the site of evolving injury in 65% of these 69 cases. Impending brachial plexopathy was most commonly noted immediately following shoulder taping and the application of counter-traction. Brachial plexus stretch upon neck extension for optimal surgical access and visualization was second in frequency-of-occurrence. Evolving traction injury to the ulnar nerve attributed to tightly-wrapped or malpositioned arms was observed in 16% of alerted cases, whereas evolving spinal cord injury following neck extension accounted for an additional 19%. This study highlights the role of tceMEP and ulnar nerve SSEP monitoring for detecting emerging peripheral nerve injury secondary to positioning in preparation for and during anterior cervical spine surgery.

Intraoperative neurophysiologic monitoring during spinal surgery.

Abstract Intraoperative neurophysiologic monitoring (IONM) is a battery of neurophysiologic tests used to assess the functional integrity of the spinal cord, nerve roots, and other peripheral nervous system structures (eg, brachial plexus) during spinal surgery. The underlying principle of IONM is to identify emerging insult to nervous system structures, pathways, and/or related vascular supply and to provide feedback regarding correlative changes in neural function before development of irreversible neural injury. IONM data provide an opportunity for intervention to prevent or minimize postoperative neurologic deficit. Current multimodality monitoring techniques permit intraoperative assessment of the functional integrity of afferent dorsal sensory spinal cord tracts, efferent ventral spinal cord motor tracts, and nerve roots. Combined use of these techniques is useful during complex spinal surgery because these monitoring modalities provide important complementary information to the surgery team.

Pedicle screws with high electrical resistance: a potential source of error with stimulus-evoked EMG.

Study Design. Clinically relevant aspects of pedicle screws were subjected to electrical resistance testing. Objectives. To catalog commonly used pedicle screws in terms of electrical resistance, and to determine whether polyaxial-type pedicle screws have the potential to create a high-resistance circuit during stimulus-evoked electromyographic testing. Summary of Background Data. Although stimulus-evoked electromyography is commonly used to confirm the accuracy of pedicle screw placement, no studies have documented the electrical resistance of commonly used pedicle screws. Methods. Resistance measurements were obtained from eight pedicle screw varieties (5 screws of each type) across the screw shank and between the shank and regions of the screw that would be clinically accessible to stimulus-evoked electromyographic testing with a screw implanted in a pedicle. To determine measurement variability, resistance was measured three times at each site and with the crown of the polyaxial-type screw in three random positions. Results. Resistance across the screw shank ranged from 0 to 36.4 ohms, whereas resistance across the length of the monoaxial-type screws ranged from 0.1 to 31.8 ohms. Resistance between the hexagonal port and shank of polyaxial-type screws ranged from 0 to 25 ohms. In contrast, resistance between the mobile crown and shank of polyaxial-type screws varied widely, ranging from 0.1 ohms to an open circuit (no electrical conduction). Polyaxial-type screws demonstrated an open circuit in 28 of 75 measurements (37%) and a high-resistance circuit (exceeding 1000 ohms) in 5 of 75 measurements (7%). Conclusions. Polyaxial-type pedicle screws have the potential for high electrical resistance between the mobile crown and shank, and therefore may fail to demonstrate an electromyographic response during stimulus-evoked electromyographic testing in the setting of a pedicle breech. To avoid false-negative stimulus-evoked electromyographic testing, the cathode stimulator probe should be applied to the hexagonal port or directly to the screw shank, and not to the mobile crown.

Transcranial Electric Motor Evoked Potential Monitoring During Spine Surgery: Is It Safe?

Study Design. Retrospective review. Objective. To report on the safety of repetitive transcranial electric stimulation (RTES) for eliciting motor-evoked potentials during spine surgery. Summary of Background Data. Theoretical concerns over the safety of RTES have hindered broader acceptance of transcranial electric motor-evoked potentials (tceMEP), despite successful implementation of spinal cord monitoring with tceMEPs in many large spine centers, as well as their apparent superiority over mixed-nerve somatosensory-evoked potentials (SSEP) for detection of spinal cord injury. Methods. The records of 18,862 consecutive patients who met inclusion criteria and underwent spine surgery with tceMEP monitoring were reviewed for RTES-related complications. Results. This large retrospective review identified only 26 (0.14%) cases with RTES-related complications; all but one of these were tongue lacerations, most of which were self-limiting. Conclusions. The results demonstrate that RTES is a highly safe modality for monitoring spinal cord motor tract function intraoperatively.

Reaction-time measures of stutterers and nonstutterers

Abstract Ten adult male stutterers and ten adult male nonstutterers participated in six reaction-time tasks designed to measure manual, acoustic, and laryngeal-region response latencies. The analysis revealed statistically significant differences between the groups for the acoustic data only. The results indicated that acoustic reaction-time differences are not accounted for by the speed of the general laryngeal response.

Training auditory-visual speech reception in adults with moderate sensorineural hearing loss.

A new method of training auditory-visual speech reception is described and evaluated on an experimental group of 12 hearing-impaired adult patients. The method involves simultaneous, live presentation of the visible and acoustic components of the therapists speech, where the acoustic signal is degraded under the therapists control with a voice-activated switch. Pre-and post-training performance was assessed with an auditory-visual sentence recognition task. The performance of the experimental group, who received 10 hours of individual training, is described and compared to a control group who received a traditional aural rehabilitation program and to a group of normals who received no training. The experimental training resulted in significantly greater improvement than the control group. A description of the training, including rationale and suggestions for implementation in a clinical setting, is provided.

Influence of nitrous oxide on posterior tibial nerve cortical somatosensory evoked potentials

The suppressive effect of the halogenated inhalation anesthesia on cortical somatosensory evoked potentials (cSSEPs) has been well documented. Less studied and appreciated is the effect of nitrous oxide often with a narcotic as an alternative to a potent agent for spinal cord monitoring. This study sought to define more clearly the influence of nitrous oxide on cSSEPs elicited to posterior tibial nerve stimulation. A secondary purpose was to demonstrate the advantage of a total intravenous propofol anesthesia in facilitating uncompromised large-amplitude cSSEPs. Fifty adult patients undergoing anterior cervical discectomy served as the study sample. Brainstem and cortical posterior tibial nerve SSEPs were recorded under two independent anesthesia conditions, namely, nitrous oxide and propofol. Results demonstrated a significant amplitude reduction and latency prolongation with the nitrous oxide versus propofol protocol. cSSEP amplitude with propofol was, on the average, approximately two times larger than that with nitrous oxide. Based on these findings, the use of nitrous-oxide anesthesia is not recommended when limited to monitoring cSSEPs that are already amplitude compromised secondary to existing spinal cord disease.

Reference threshold sound‐pressure levels for the TDH‐50 and ER‐3A earphones

Reference threshold sound-pressure levels were established for a new insert earphone, the ER-3A tubephone, and for the TDH-50 earphone. In test-retest comparisons, the tubephone produced estimates of auditory threshold as reliable as the thresholds produced by the supraaural earphone. Reference thresholds were developed for the two earphones from data contributed by three laboratories. While the TDH-50 data are in good agreement with the provisional ANSI 6-cc coupler reference levels (ASHA, 1982), the ER-3A data are at variance with the manufacturers provisional recommendation for 2-cc coupler reference thresholds for frequencies below 1 kHz. The differences are attributed to physiologic noise that masked the lower frequency thresholds.

Epidural hematoma causing dense paralysis after anterior cervical corpectomy. A report of two cases.

P aralysis after anterior cervical spine surgery is an uncommon, albeit devastating, complication. Flynn analyzed data from 36,657 anterior cervical interbody arthrodeses performed by 704 neurosurgeons and noted that only 100 patients (0.3%) had a permanent neurologic deficit1. Seventy-five percent of these patients exhibited symptoms of a neurologic deficit immediately on emergence from anesthesia, whereas 25% exhibited symptoms early in the postoperative recovery period. The most common causes of spinal cord injury during cervical spine surgery include surgical trauma, vascular compromise, graft impingement, instrument misplacement, and spinal manipulation. One of the less common complications that can cause major neurologic morbidity is an expanding epidural hematoma at the surgical site. A hematoma can develop slowly in the corpectomy or discectomy site and may cause compression of the spinal cord. Unfortunately, there is a dearth of literature addressing this issue2,3. This scarcity may be due not only to the exceptionally low prevalence of a compressive hematoma but also to the difficulty in defining the exact cause of paralysis after surgery1. Multimodality neurophysiological monitoring has proven to be highly beneficial in minimizing spinal cord injury during spine surgery4-10. Recent evidence has shown marked improvement in the sensitivity to injury detection during cervical spine surgery with transcranial electric motor evoked potential (tceMEP) monitoring compared with somatosensory evoked potential (SSEP) monitoring alone7,8. We present the cases of two patients to highlight the role of tceMEP monitoring in the early detection and intervention of an expanding epidural hematoma. Our patients were informed that data from the cases would be submitted for publication. C ase 1. A seventy-four-year-old man with symptoms of progressive cervical myelopathy underwent an anterior cervical corpectomy and arthrodesis for decompression of the spinal cord. The spinal cord …