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P27.11 Excitatory and inhibitory effects of internal globus pallidus stimulation on pallidal neurons
Posters / Clinical Neurophysiology 117 (2006) S121–S336
P27.9 Intraoperative neurophysiological monitoring of pudendal nerve activity during pudendal nerve implant for neurogenic overactive bladder S. Malaguti, M. Spinelli Niguarda Hospital, Neurourophysiology Spinal Unit, Italy Background: The pudendal nerve (PN) innervates the pelvic floor muscles, sphincters and pelvic organs. The therapeutic effect of inhibition of overactive detrusor contractions applying electrical stimulation in perineal area is already known. Aim: To stimulate PN in a chronic setting we developed a minimally invasive approach to place the lead in order to treat neurogenic patients. To correlate bladder behaviour with neural activity we therefore recorded neural traffic (afferent and efferent) from the PN lead during cystomanometry (CM). Material and methods: Four female pts (21–53 years) with neurogenic overactive bladder (two vascular myelopathy and two traumatic spinal cord lesion) non responder to antimuscarinic drugs were submitted to a complete neurophysiological and urodynamic assessment at baseline; the implant of the lead was done using neurophysiological monitoring. An acute test of PN stimulation was performed during CM in response to the uninhibited bladder contractions. Results: Acute stimulation of PN (5 Hz, 0.2 ms, intensity corresponding to the bulbocavernosus reflex), during the filling phase of cystomanometry (20 ml/min) was effective in determine detrusor inhibition of contraction leading to an increase in bladder capacity. During the filling phase a rising afferent PN activity until the emergence of first uninhibited bladder contraction was recorded until the acute stimulation of PN caused an increase in efferent activity resulting in loss of bladder contraction. Conclusion: Neurophysiological guidance is mandatory to place a lead for chronic stimulation and to record on-going neural activity of PN during CM. Further study must carried out to identify the best stimulation parameter and to optimize the method in order to allow a PN stimulation on physiologic demand. doi:10.1016/j.clinph.2006.06.463
P27.10 Motor evoked potential monitoring during the dorsal root entry zone (DREZ) procedure A. Husain, K. Ashton, D. Shah, S. Elliott Duke University Medical Center, Medicine (Neurology), USA Background: In the spinal cord dorsal root entry zone (DREZ) procedure the dorsal root entry zone is thermocoagulated with a radio frequency (RF) probe. Morbidity of this procedure is related to extension to the lesion to
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involve the pyramidal tract. Consequently weakness is common complication of this surgery and occurs in up to 5–10% of patients. Aim(s)/objective(s): To see if neurophysiologic intraoperative monitoring (NIOM) could be used to test the location of the DREZ electrode to confirm that it is not too close to the pyramidal tract. Patients and methods: All patients undergoing spinal cord DREZ procedures since 1999 at our institution underwent NIOM. After induction of anesthesia, needle electrodes were inserted into selected ipsilateral upper and lower extremity muscles to monitor motor evoked potentials (MEP). After exposure, the DREZ electrode was inserted into the site to be lesioned and connected to a stimulator. Stimulation intensity was gradually increased to 1 V. If a MEP was noted with intensity less than 1 V, the DREZ electrode was repositioned; if no activation was noted, a lesion was made. The same procedure was repeated for all lesions. Results: Fifteen patients underwent NIOM during spinal cord DREZ procedure. Thirteen underwent a cervical DREZ procedure, one each underwent a thoracic and lumbar DREZ procedure. A mean of 53 lesions were made for each patient. Twelve (80%) patients had significant pain relief, two (13%) had some pain relief, and one (7%) did not improve after the procedure. None of the patients had new or worsened ipsilateral weakness. In four (27%) patients EMG activation was noted with stimulation intensity less than 1 V, and the DREZ electrode was repositioned prior to lesioning. Conclusions: MEP monitoring during spinal cord DREZ procedures can reduce the incidence of postoperative weakness. doi:10.1016/j.clinph.2006.06.464
P27.11 Excitatory and inhibitory effects of internal globus pallidus stimulation on pallidal neurons E. Pralong 1, D. Debatisse 1, C. Pollo 2, J.G. Villemure 1 1 2
CHUV, NCH, Switzerland NCH, Switzerland
Background: Besides clinical efficacy, the mechanisms of action of deep brain stimulation (DBS) are still debated. Factors such as DBS electrode location, stimulating frequency or local versus distant sites of action make unlikely that DBS acts through a single mechanism. One major drawback in understanding DBS effects is that two electrodes (one DBS electrode and one microrecording electrode) are very seldom placed in the same structure. Objectives: To shed light on this complex issue, we have taken the opportunity to record the response of globus pallidus neurons to 100 Hz stimulations in a case of Lesch– Nyhan syndrome (LNS) where four pallidal electrodes were implanted.
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Posters / Clinical Neurophysiology 117 (2006) S121–S336
Methods: The stimulating electrodes were positioned in the center of the anterior portion of the globus pallidus internus (GPi, +5.9 mm AP, 13.8 mm LAT, and +0.7 mm VERT). Fifteen neurons were recorded before and after 100 Hz DBS stimulation at 6 mA and 0.1 ms duration on each posterior pallidum (+1.6 mm AP, 18.2 mm LAT, and 0.5 mm VERT). Results: Three types of response were observed, 5/15 neurons were inhibited during the 10 s epoch immediately after DBS stimulation. This effect was followed by a rebound increase in firing rate. Most of the inhibited neurons were located in the homolateral GPi. 6/15 neurons were unaffected by DBS and 4/15 neurons were stimulated immediately after DBS stimulation these neurons were observed in the globus pallidus externus (GPe). Discussion: These observations support the fact the GPi DBS in a case of LNS exercises two main actions. Locally DBS induces a reversible inhibition of neuron firing rate while at the same time distantly exciting the main afferents to and/or efferents from the GPi. Conclusion: It would be tempting to associate local inhibition to depolarizing block or synaptic inhibition while distant excitation could represent antidromic excitation of GPe projection neurons. Both actions could explain the clinical effect of DBS in LNS. doi:10.1016/j.clinph.2006.06.465
P27.12 Non-invasive peri-spinal oximetry for aortic coarctation repair M.E. Mitchell 1, A. Sehic 2, H.L. Edmonds Jr 2, E.H. Austin III 1 1 2
University of Louisville, Louisville, Kentucky, USA Surgical Monitoring Associates Inc., USA
Background: Although near-infrared spectroscopy (NIRS) has been used in adults to assess tissue oxygen saturation changes in the peri-spinal microvasculature during repair of thoracoabdominal aneurysms, its use has not been described in infants. The purpose of this study was to characterize tissue oxygen saturation at the T10 level in neonates and children undergoing repair of aortic coarctation. Methods: Ten neonates (<30 days old) and four children (ages 4–11 years) with aortic coarctation were enrolled in the study. Cerebral and peri-spinal regional oxygen saturations (C-rSO2 and S-rSO2) were measured by NIRS sensors (SomaSensors, Somanetics Corp., Troy, MI) placed on the left forehead and lower thoracic dorsal midline at the level of T10. All measurements were made at 1 min intervals. Ten baseline measurements were made on each patient prior to incision. These were averaged and all subsequent values are reported as percent change from baseline. Results: Neonates demonstrated significant percent drop in S-rSO2 from baseline during each minute following
application of cross clamp while there was no significant change in saturation in older children. Neonates demonstrated return to baseline saturation after cross clamp removal in all cases. Conclusions: Spinal oximetry in the smallest children is interpretable. Neonates with severe aortic coarctation exhibit a significant drop in lower body tissue saturation during cross clamp, a drop that is not seen in older children. These findings suggest that collateral blood supply is limited in the neonate with coarctation, and perhaps that clamp times are more critical in this group of patients. Neurophysiologic measurement of motor pathway function will help clarify the clinical significance of these observations. doi:10.1016/j.clinph.2006.06.466
P27.13 How to analyse the results in neurophysiologic intraoperative monitoring in scoliosis J. Conill 1, N. Ventura 2, A. Ey 2, E. Monclus 3 1
Hospital Universitari Sant Joan de Deu, Neurophysiology, Spain 2 Hospital Universitari Sant Joan de Deu, Orthopaedics, Spain 3 Hospital Universitari Sant Joan de Deu, Anaesthesiology, Spain Background: Results in neurophysiologic intraoperative monitoring (IOM) in scoliosis have been classified as true/false positive/negative, while it was detected or not a change in the potentials that anticipate or not post-operative sequels. We consider that this classification is not useful enough for comparing neither IOM results among different series, nor results among patients of a single series. Aim: We propose a classification for IOM results in scoliosis with four groups. (A) No changes in potentials. (B) Transient changes. (C) Permanent changes. (D) Potentials disappeared. We have revised our series of 189 IOM in scoliosis done in the last 5 years. Methods: Cortical somatosensory evoked potentials (SEPc) stimulating sciatic nerve and control of motor pathways by multipulse transcraneal electric stimulation (mTES) recording potentials in tibial anterior and abductor hallucis in both legs (MEP). We have monitored 189 scoliosis, 119 idiopathic (21 males and 98 females) and 70 others scoliosis (31 males and 39 females). Age ranged from 2 to 20 years. Posterior instrumentation was done in 145 cases, 20 anterior, and 24 by both approaches. Anaesthesia by propofol, fentanyl and atracurium; besides controlled hypotension. Results: Group A 123 (65%), B 48 (25%), C 18 (10%) and D no one. Discussion: The cases classified as false-positive until now are those that justify the existence of IOM. It is neces-
P27.9 Intraoperative neurophysiological monitoring of pudendal nerve activity during pudendal nerve implant for neurogenic overactive bladder S. Malaguti, M. Spinelli Niguarda Hospital, Neurourophysiology Spinal Unit, Italy Background: The pudendal nerve (PN) innervates the pelvic floor muscles, sphincters and pelvic organs. The therapeutic effect of inhibition of overactive detrusor contractions applying electrical stimulation in perineal area is already known. Aim: To stimulate PN in a chronic setting we developed a minimally invasive approach to place the lead in order to treat neurogenic patients. To correlate bladder behaviour with neural activity we therefore recorded neural traffic (afferent and efferent) from the PN lead during cystomanometry (CM). Material and methods: Four female pts (21–53 years) with neurogenic overactive bladder (two vascular myelopathy and two traumatic spinal cord lesion) non responder to antimuscarinic drugs were submitted to a complete neurophysiological and urodynamic assessment at baseline; the implant of the lead was done using neurophysiological monitoring. An acute test of PN stimulation was performed during CM in response to the uninhibited bladder contractions. Results: Acute stimulation of PN (5 Hz, 0.2 ms, intensity corresponding to the bulbocavernosus reflex), during the filling phase of cystomanometry (20 ml/min) was effective in determine detrusor inhibition of contraction leading to an increase in bladder capacity. During the filling phase a rising afferent PN activity until the emergence of first uninhibited bladder contraction was recorded until the acute stimulation of PN caused an increase in efferent activity resulting in loss of bladder contraction. Conclusion: Neurophysiological guidance is mandatory to place a lead for chronic stimulation and to record on-going neural activity of PN during CM. Further study must carried out to identify the best stimulation parameter and to optimize the method in order to allow a PN stimulation on physiologic demand. doi:10.1016/j.clinph.2006.06.463
P27.10 Motor evoked potential monitoring during the dorsal root entry zone (DREZ) procedure A. Husain, K. Ashton, D. Shah, S. Elliott Duke University Medical Center, Medicine (Neurology), USA Background: In the spinal cord dorsal root entry zone (DREZ) procedure the dorsal root entry zone is thermocoagulated with a radio frequency (RF) probe. Morbidity of this procedure is related to extension to the lesion to
S237
involve the pyramidal tract. Consequently weakness is common complication of this surgery and occurs in up to 5–10% of patients. Aim(s)/objective(s): To see if neurophysiologic intraoperative monitoring (NIOM) could be used to test the location of the DREZ electrode to confirm that it is not too close to the pyramidal tract. Patients and methods: All patients undergoing spinal cord DREZ procedures since 1999 at our institution underwent NIOM. After induction of anesthesia, needle electrodes were inserted into selected ipsilateral upper and lower extremity muscles to monitor motor evoked potentials (MEP). After exposure, the DREZ electrode was inserted into the site to be lesioned and connected to a stimulator. Stimulation intensity was gradually increased to 1 V. If a MEP was noted with intensity less than 1 V, the DREZ electrode was repositioned; if no activation was noted, a lesion was made. The same procedure was repeated for all lesions. Results: Fifteen patients underwent NIOM during spinal cord DREZ procedure. Thirteen underwent a cervical DREZ procedure, one each underwent a thoracic and lumbar DREZ procedure. A mean of 53 lesions were made for each patient. Twelve (80%) patients had significant pain relief, two (13%) had some pain relief, and one (7%) did not improve after the procedure. None of the patients had new or worsened ipsilateral weakness. In four (27%) patients EMG activation was noted with stimulation intensity less than 1 V, and the DREZ electrode was repositioned prior to lesioning. Conclusions: MEP monitoring during spinal cord DREZ procedures can reduce the incidence of postoperative weakness. doi:10.1016/j.clinph.2006.06.464
P27.11 Excitatory and inhibitory effects of internal globus pallidus stimulation on pallidal neurons E. Pralong 1, D. Debatisse 1, C. Pollo 2, J.G. Villemure 1 1 2
CHUV, NCH, Switzerland NCH, Switzerland
Background: Besides clinical efficacy, the mechanisms of action of deep brain stimulation (DBS) are still debated. Factors such as DBS electrode location, stimulating frequency or local versus distant sites of action make unlikely that DBS acts through a single mechanism. One major drawback in understanding DBS effects is that two electrodes (one DBS electrode and one microrecording electrode) are very seldom placed in the same structure. Objectives: To shed light on this complex issue, we have taken the opportunity to record the response of globus pallidus neurons to 100 Hz stimulations in a case of Lesch– Nyhan syndrome (LNS) where four pallidal electrodes were implanted.
S238
Posters / Clinical Neurophysiology 117 (2006) S121–S336
Methods: The stimulating electrodes were positioned in the center of the anterior portion of the globus pallidus internus (GPi, +5.9 mm AP, 13.8 mm LAT, and +0.7 mm VERT). Fifteen neurons were recorded before and after 100 Hz DBS stimulation at 6 mA and 0.1 ms duration on each posterior pallidum (+1.6 mm AP, 18.2 mm LAT, and 0.5 mm VERT). Results: Three types of response were observed, 5/15 neurons were inhibited during the 10 s epoch immediately after DBS stimulation. This effect was followed by a rebound increase in firing rate. Most of the inhibited neurons were located in the homolateral GPi. 6/15 neurons were unaffected by DBS and 4/15 neurons were stimulated immediately after DBS stimulation these neurons were observed in the globus pallidus externus (GPe). Discussion: These observations support the fact the GPi DBS in a case of LNS exercises two main actions. Locally DBS induces a reversible inhibition of neuron firing rate while at the same time distantly exciting the main afferents to and/or efferents from the GPi. Conclusion: It would be tempting to associate local inhibition to depolarizing block or synaptic inhibition while distant excitation could represent antidromic excitation of GPe projection neurons. Both actions could explain the clinical effect of DBS in LNS. doi:10.1016/j.clinph.2006.06.465
P27.12 Non-invasive peri-spinal oximetry for aortic coarctation repair M.E. Mitchell 1, A. Sehic 2, H.L. Edmonds Jr 2, E.H. Austin III 1 1 2
University of Louisville, Louisville, Kentucky, USA Surgical Monitoring Associates Inc., USA
Background: Although near-infrared spectroscopy (NIRS) has been used in adults to assess tissue oxygen saturation changes in the peri-spinal microvasculature during repair of thoracoabdominal aneurysms, its use has not been described in infants. The purpose of this study was to characterize tissue oxygen saturation at the T10 level in neonates and children undergoing repair of aortic coarctation. Methods: Ten neonates (<30 days old) and four children (ages 4–11 years) with aortic coarctation were enrolled in the study. Cerebral and peri-spinal regional oxygen saturations (C-rSO2 and S-rSO2) were measured by NIRS sensors (SomaSensors, Somanetics Corp., Troy, MI) placed on the left forehead and lower thoracic dorsal midline at the level of T10. All measurements were made at 1 min intervals. Ten baseline measurements were made on each patient prior to incision. These were averaged and all subsequent values are reported as percent change from baseline. Results: Neonates demonstrated significant percent drop in S-rSO2 from baseline during each minute following
application of cross clamp while there was no significant change in saturation in older children. Neonates demonstrated return to baseline saturation after cross clamp removal in all cases. Conclusions: Spinal oximetry in the smallest children is interpretable. Neonates with severe aortic coarctation exhibit a significant drop in lower body tissue saturation during cross clamp, a drop that is not seen in older children. These findings suggest that collateral blood supply is limited in the neonate with coarctation, and perhaps that clamp times are more critical in this group of patients. Neurophysiologic measurement of motor pathway function will help clarify the clinical significance of these observations. doi:10.1016/j.clinph.2006.06.466
P27.13 How to analyse the results in neurophysiologic intraoperative monitoring in scoliosis J. Conill 1, N. Ventura 2, A. Ey 2, E. Monclus 3 1
Hospital Universitari Sant Joan de Deu, Neurophysiology, Spain 2 Hospital Universitari Sant Joan de Deu, Orthopaedics, Spain 3 Hospital Universitari Sant Joan de Deu, Anaesthesiology, Spain Background: Results in neurophysiologic intraoperative monitoring (IOM) in scoliosis have been classified as true/false positive/negative, while it was detected or not a change in the potentials that anticipate or not post-operative sequels. We consider that this classification is not useful enough for comparing neither IOM results among different series, nor results among patients of a single series. Aim: We propose a classification for IOM results in scoliosis with four groups. (A) No changes in potentials. (B) Transient changes. (C) Permanent changes. (D) Potentials disappeared. We have revised our series of 189 IOM in scoliosis done in the last 5 years. Methods: Cortical somatosensory evoked potentials (SEPc) stimulating sciatic nerve and control of motor pathways by multipulse transcraneal electric stimulation (mTES) recording potentials in tibial anterior and abductor hallucis in both legs (MEP). We have monitored 189 scoliosis, 119 idiopathic (21 males and 98 females) and 70 others scoliosis (31 males and 39 females). Age ranged from 2 to 20 years. Posterior instrumentation was done in 145 cases, 20 anterior, and 24 by both approaches. Anaesthesia by propofol, fentanyl and atracurium; besides controlled hypotension. Results: Group A 123 (65%), B 48 (25%), C 18 (10%) and D no one. Discussion: The cases classified as false-positive until now are those that justify the existence of IOM. It is neces-