Faculty Bibliography
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Limiting the current density during localization of the primary motor cortex by using a tangential-radial cortical somatosensory evoked potentials model, direct electrical cortical stimulation, and electrocorticography
BACKGROUND:Traditionally, the dual-radial model, which requires high cortical stimulation intensities and may evoke intraoperative seizures, is used for mapping during resection of lesions within or near the central sulcus. OBJECTIVE:To examine the potential utility of using the multimodal tangential-radial triphasic model, which may increase the accuracy and reliability of cortical mapping at lower stimulation intensities. METHODS:We performed a retrospective review of intracranial neuromonitoring cases at the University of Virginia. The tangential-radial triphasic model used direct electrical cortical stimulation (DECS), electrocorticography, and somatosensory evoked potentials with an additional P25 peak for waveform interpretation, instead of the older dual-radial model with N20 and P30 peaks alone. The central sulcus and sensory cortex were localized by generating multiple sensory maps. DECS with 50-Hz frequency was applied. Electrocorticography was used for detection of afterdischarges. RESULTS:Fifteen consecutive intracranial cases were identified. The patients consisted of 8 males and 7 females ranging in age from 12 to 74 years (median, 53 years). Fourteen patients had an intra-axial cortical mass, and 1 patient had a cortical arteriovenous malformation. The DECS thresholds ranged from 3.7 to 12 mA (median, 6.2 mA). Localization of motor and sensory cortices was accurately performed at low thresholds with bipolar DECS in all patients. Intraoperative seizures occurred in 1 patient (7%), and new permanent postoperative functional deficits occurred in 1 patient (7%). CONCLUSION/CONCLUSIONS:Our mapping technique appears safe and reliable for resection near the central sulcus. The tangential-radial triphasic model allows for lower stimulation intensities, reducing the risk of intraoperative seizures.
PMID: 21562433
ISSN: 1524-4040
CID: 5030982
Preventing position-related brachial plexus injury with intraoperative somatosensory evoked potentials and transcranial electrical motor evoked potentials during anterior cervical spine surgery [Case Report]
The use of somatosensory evoked potentials (SSEPs) to monitor upper extremity nerves during surgery is becoming more accepted as a valid and useful technique to minimize intraoperative nerve injuries. We present a case illustrating the benefit of utilizing both SSEPs and transcranial electrical motor evoked potentials (TCeMEPs) for preventing position-related injury during surgery. The patient was a 43-year-old male with a history of neck pain, along with numbness and tingling of the upper extremities. While the patient was being draped, upper extremity SSEPs diminished significantly TCeMEP responses in the hands (abductor pollicus brevis-abductor digiti minimi; APB-ADM) vanished shortly after that, followed by the biceps and left deltoid. The surgeons were notified, and the tape on the shoulders was loosened. No improvements were noted in SSEPs nor TCeMEPs due to this intervention, so all tape was removed and the patient's arms were allowed to rest naturally upon the arm boards. Upper extremity TCeMEP responses could then be elicited and SSEPs improved shortly afterward. Surgery was completed with the arms on the arm boards. All signals remained stable for the remaining three hours of the procedure. At two months follow-up, the patient was well with total pain relief and normal upper extremity function when neurological examination was performed. This report demonstrates a case in which intraoperative neurophysiological monitoring was useful in identifying and reversing impending nerve injury during cervical spine surgery. Significant changes were seen in SSEPs as well as TCeMEPs, so we recommend that TCeMEP monitoring be considered as an adjunct to SSEPs for prevention of injury to the brachial plexus.
PMID: 21988038
ISSN: 1086-508x
CID: 5030992
Protecting the genitofemoral nerve during direct/extreme lateral interbody fusion (DLIF/XLIF) procedures [Case Report]
A 77-year-old male presented with a history of severe lower back pain for 10 years with radiculopathy, positive claudication type symptoms in his calf with walking, and severe "burning" in his legs bilaterally with walking. Magnetic resonance imaging (MRI) revealed lumbar stenosis at the L3-L4 and L4-L5 levels. During the direct or extreme lateral interbody fusion (DLIF/XLIF) procedure, bilateral posterior tibial, femoral, and ulnar nerve somatosensory evoked potentials (SSEPs) were recorded with good morphology of waveforms observed. Spontaneous electromyography (S-EMG) and triggered electromyography (T-EMG) were recorded from cremaster and ipsilateral leg muscles. A left lateral retroperitoneal transpsoas approach was used to access the anterior disc space for complete discectomy, distraction, and interbody fusion. T-EMG ranging from 0.05 to 55.0 mA with duration of 200 microsec was used for identification of the genitofemoral nerve using a monopolar stimulator during the approach. The genitofemoral nerve (L1-L2) was identified, and the guidewire was redirected away from the nerve. Post-operatively, the patient reported complete pain relief and displayed no complications from the procedure. Intraoperative SSEPs, S-EMG, and T-EMG were utilized effectively to guide the surgeon's approach in this DLIF thereby preventing any post-operative neurological deficits such as damage to the genitofemoral nerve that could lead to groin pain.
PMID: 21313792
ISSN: 1086-508x
CID: 5030972
Sawtooth wave density analysis during REM sleep in temporal lobe epilepsy patients
BACKGROUND AND PURPOSE/OBJECTIVE:This study analyzes sawtooth waves (STW), a characteristic feature of rapid eye movement (REM) sleep, in temporal lobe epilepsy patients in order to test the hypothesis of STW dysfunction in this population. METHODS:Polysomnographic records from 16 patients with temporal lobe epilepsy and 11 controls were scored for density (STW/h of REM sleep), duration (STW duration in s), and frequency of STW (waves/second within each STW complex). These measures were compared between both groups. RESULTS:STW measures were significantly different in control vs. epilepsy patients; respectively, density was 60.8 vs. 20.9 waves/h (P<0.005), average duration was 6.5 vs. 5.4 s (P<0.005 cycles 1-4), and frequency was 2.75 vs. 2.61 Hz (P<0.0005 across all cycles). CONCLUSIONS:Our measurements show a change in the density, duration and frequency of STW in patients with temporal lobe epilepsy compared to controls. Other parameters of REM sleep appear to be similar in both groups. These findings suggest a cortical influence on REM sleep either directly or through limbic-hypothalamic-brainstem connections.
PMID: 15946900
ISSN: 1389-9457
CID: 5030962
Fingertip skin conformance accounts, in part, for differences in tactile spatial acuity in young subjects, but not for the decline in spatial acuity with aging
The ability of the skin to conform to the spatial details of a surface or an object is an essential part of our ability to discriminate fine spatial features haptically. In this study, we examined the extent to which differences in tactual acuity between subjects of the same age and between younger and older subjects can be accounted for by differences in the properties of the skin. We did so by measuring skin conformance and tactile spatial acuity in the glabrous skin at the fingertip in 18 younger (19-36 years old) and 9 older (61-69 years old) subjects. Skin conformance was measured as the degree to which the skin invaded the spaces in the psychophysical stimuli. There were several findings. First, skin conformance accounted for 50% of the variance in our measure of tactile spatial acuity (the threshold for grating orientation discrimination) between the younger subjects. The subjects with more compliant skin had substantially lower thresholds than did the subjects with stiffer skin. Second, the skin of the younger subjects was more compliant across than along the skin ridges, and this translated into significantly greater performance when the gratings were oriented along than when oriented across the skin. Third, skin conformance was virtually identical in the younger and the older subjects. Consequently, skin conformance cannot account for the loss of spatial acuity reported in earlier studies and confirmed in this study. We infer that the loss must be neural in origin.
PMID: 15095940
ISSN: 0031-5117
CID: 5030952
Spatial acuity after digit amputation
Digit amputation in human and non-human primates results in reorganization of somatosensory cortex in which the representations of adjacent, intact digits expand to fill the cortical region previously devoted to the amputated digits. Whether this expanded representation results in improved sensory performance has not been determined. Consequently, we measured the ability to recognize small objects (raised letters) with a digit adjacent to the amputation and the same digit on the normal, contralateral hand in 15 amputees. The same digits were also tested in 15 age-matched, amputation-free subjects. There was no significant difference in recognition scores between digits in the amputees or between amputees and control subjects. More detailed analyses of specific confusion patterns and of the improvement with practice showed no significant differences. As far as we could determine, the cortical expansion that is presumed to accompany digit amputation had no effect on tactile pattern recognition performance.
PMID: 12023314
ISSN: 0006-8950
CID: 5030942
Phase II studies of the glycine antagonist GV150526 in acute stroke - The North American experience [Meeting Abstract]
Background and Purpose-GV150526, a selective glycine site antagonist, reduces infarct volume in rats with focal cerebral ischemia. Safety and efficacy in humans with acute stroke are being investigated, We sought to further explore the safety. pharmacokinetics, and preliminary outcome of GV150526 treatment in patients with a clinical diagnosis of acute stroke. Methods-Two trials were conducted in North America. The North American Glycine Antagonist in Neuroprotection trial (GAIN 1) (GLYA2001; United States only) was designed as a sequential dose escalation study. GAIN 2 (GLYA2005; United States and Canada) was designed to further assess the safety of the highest dose tolerated in GAIN 1. Both trials were randomized (2:1), double-blind, and placebo controlled, Treatment was started within 12 hours of symptom onset; patients with both ischemic stroke and primary intracerebral hemorrhage were included in both trials. Results-The dose escalation study (GAIN 1) completed 3 dosing tiers. Enrollment was suspended before escalation to the fourth tier because of laboratory reports of transiently elevated bilirubin levels in a concurrent European study that employed the dose targeted for this tier. After review by an independent safety committee of the worldwide safety data, the second study (GAIN 2) commenced. One hundred nine patients were randomized and dosed with study drug, either an 800-mg loading dose followed by 200 mg every 12 hours for 3 days of GV150526 or placebo. The incidence of serious adverse events was similar in the drug and placebo groups. Mild irritation at the infusion site and symptoms suggestive of mild and reversible altered mentation were reported more frequently in the GV150526 group than in the placebo group. Hyperbilirubinemia was reported in 6% of GV150526-treated patients compared with 3% of placebo-treated patients. Outcome at 4 weeks after stroke was better in GV150526-treated patients, but the studies were not powered to show statistical significance, and the baseline neurological deficits in the GV150526-treated patients were less severe. Conclusions-These preliminary studies suggest that GV150526 is well tolerated by patients with suspected acute stroke. Further pivotal studies testing the efficacy and safety of GV150526 in acute stroke are ongoing.
ISI:000085039900003
ISSN: 0039-2499
CID: 2739162
