Decrease In Somatosensory Evoked Potentials Amplitude Research Articles

ID 10 – A novel electrophysiological method in the diagnosis of pudendal neuropathy: Position related changes in pudendal sensory evoked potentials

Pudendal nerve entrapment (PNE) is a common cause of resistant and disabling perineal pain. Although it is diagnosed clinically, neurophysiological tests are used for the diagnosis. Since the complaints worsen in the sitting position, routine pudendal somatosensory evoked potentials (SEP) performed in the supine position with midline stimulation may fail to show the PNE. We hypothesized that diagnostic value of SEP can be increased by stimulating the right and left sides separately along with provocation by maintained sitting position (dynamic SEP). Forty-nine patients with PNE and 16 healthy controls were included. SEP recordings were performed by stimulating the dorsal nerve of penis/clitoris on either side. The recordings were performed at the first supine position, at the beginning and end of a standardized sitting posture and at the second supine position. Regarding the patients with recordable responses, we might suggest that approximately 45% decrease in SEP amplitude or an amplitude value less than 1.5 mV at the termination of the sitting position (and their reversal with switching to the supine position again) are the parameters to be used with high selectivity. The dynamic pudendal SEP study described herein seems to be more valuable in PNE diagnosis than conventional SEPs.

Multimodality intraoperative monitoring during complex lumbosacral procedures: indications, techniques, and long-term follow-up review of 61 consecutive cases.

The purpose of this study was to examine the neurological outcomes after complex lumbosacral surgery in patients undergoing multimodality neurophysiological monitoring. Sixty-one patients were consecutively enrolled in this study. These patients underwent complex intra- and extradural lumbosacral procedures with concomitant intraoperative electromyography (EMG) monitoring of the lower-limb muscles, external anal and urethral sphincters (EAS and EUS), and lower-limb somatosensory evoked potentials (SSEPs). Long-term (minimum 2-year) clinical follow-up data were obtained in all cases. Most patients were treated for spinal/spinal cord tumors (61%) or adult tethered cord syndrome (25%). Recordable lower-extremity SSEPs were reported in 54 patients (89%). New postoperative neurological deficits occurred in only three patients (4.9%), and remained persistent in only one patient (1.6%) at long-term follow-up examination. In only one of these cases was a significant decrease in SSEP amplitude detected. Spontaneous EMG activity was observed in the lower-extremity muscles and/or EAS and EUS in 51 cases (84%). Intraoperatively, EMG demonstrated activity only in the EUS in 5% of patients and only in the EAS in 28%. In seven patients (11%) spontaneous intraoperative EMG activity was observed in both the EAS and the EUS; however, in only three of these cases was EMG activity recorded in both sphincters simultaneously. In addition to spontaneously recorded EMG activity, electrically evoked EMG activity was also used as an intraoperative adjunct. A bipolar stimulating electrode was used to identify functional neural tissue before undertaking microsurgical dissection in 58 individuals (95%). In the majority of these patients, evoked EMG activity occurred either in one (33%) or in two muscles (9%) simultaneously. The presence of electrically evoked EMG activity in structures encountered during microdissection altered the plan of treatment in 24 cases (42%). The authors conclude that the combined SSEP and EMG monitoring of lower-limb muscles, EAS, and EUS is a practical and reliable method for obtaining optimal electrophysiological feedback during complex neurosurgical procedures involving the conus medullaris and cauda equina. Analysis of the results indicates that these intraoperative adjunctive modalities positively influence decision making with regard to microsurgery and reduce the risk of perioperative neurological complications. Validation of the clinical value of these approaches, however, will require further assessment in a larger prospective cohort of patients.

Neurophysiologic effects of retrograde cerebral perfusion used for aortic reconstruction

Objective: The results of neurophysiologic monitoring using somatosensory evoked potentials (SSEPs) and electroencephalography (EEG) were analyzed to determine if retrograde cerebral perfusion (RCP) supported central nervous system electrical function during surgery that required temporary interruption of antegrade cerebral perfusion (IACP).Design: A prospective, observational study.Setting: A university hospital.Participants: Fifteen adult patients who underwent aortic reconstruction using RCP and three patients who underwent thoracic aortic operations using hypothermic circulatory arrest without RCP.Interventions: SSEPs and EEG were monitored continuously throughout the operation. Regression analysis was performed to determine the factors that affected the rate of decrease in SSEP amplitudes during IACP and the time required for SSEP and EEG activity to recover after antegrade cerebral perfusion (ACP) was restored.Measurements and Main Results: The amplitude of SSEPs that were elicited decreased over time after IACP The mean ± standard deviation (SD) time required for the brachial plexus (Erb's point), cervicomedullary junction (N13), and brainstem (N18) SSEPs to decrease to 0.5 of their original amplitude after IACP were 30 ± 2, 19 ± 2, and 16 ± 2 minutes, respectively. The rate of decrease in the N18 SSEP amplitude after IACP correlated positively to the fraction of no-flow time (p = 0.01).Conclusion: RCP attenuated the rate of decay in SSEP amplitudes during IACP. This suggested that RCP had a measurable physiologic effect on central nervous system function and may increase the time that ACP can be safely interrupted.

Changes in the Somatosensory Evoked Potential During and Immediately Following Temporary Middle Cerebral Artery Occlusion Predict Somatosensory Cortex Ischemic Lesions in Monkeys

Somatosensory evoked potentials (SEP) were recorded during and immediately following temporary middle cerebral artery (MCA) occlusion to determine whether they can be used to predict ischemic lesions to the somatosensory cortex (SI). Twenty-one cynomolgus female monkeys were subjected to four different MCA occlusion durations (15-60 min) during hypotension (45-50 mm Hg mean arterial blood pressure). The amplitude and central conduction time (CCT) of the median nerve SEP were recorded preceding, during, and following occlusion. Two groups were established based on the development of SI ischemic lesions: animals developing SI lesions formed the SI-lesion group (n = 9), and animals without ischemic lesions or with lesions outside the SI cortex formed the SI-spared group (n = 12). Changes in the SEP during and following MCA occlusion under conditions of hypotension were similar to those reported by others. The SEP disappeared in all animals within 15 min of occlusion and reappeared 5 min following reperfusion. Several differences were observed between the SI-lesion and SI-spared groups. The SI-lesion group had a more rapid decrease in SEP amplitude during the first 5 min of occlusion and had smaller SEP amplitudes and longer CCTs during reperfusion. These results suggest that changes in SEP amplitude and latency during and immediately following temporary MCA occlusion predict development of SI ischemic lesions.

The use of a mixed weibull model in occupational injury analysis : M.K. Chung, Journal of Occupational Accidents, February 1986, 7(4), 239–250

Objective: The results of neurophysiologic monitoring using somatosensory evoked potentials (SSEPs) and electroencephalography (EEG) were analyzed to determine if retrograde cerebral perfusion (RCP) supported central nervous system electrical function during surgery that required temporary interruption of antegrade cerebral perfusion (IACP).Design: A prospective, observational study.Setting: A university hospital.Participants: Fifteen adult patients who underwent aortic reconstruction using RCP and three patients who underwent thoracic aortic operations using hypothermic circulatory arrest without RCP.Interventions: SSEPs and EEG were monitored continuously throughout the operation. Regression analysis was performed to determine the factors that affected the rate of decrease in SSEP amplitudes during IACP and the time required for SSEP and EEG activity to recover after antegrade cerebral perfusion (ACP) was restored.Measurements and Main Results: The amplitude of SSEPs that were elicited decreased over time after IACP The mean ± standard deviation (SD) time required for the brachial plexus (Erb's point), cervicomedullary junction (N13), and brainstem (N18) SSEPs to decrease to 0.5 of their original amplitude after IACP were 30 ± 2, 19 ± 2, and 16 ± 2 minutes, respectively. The rate of decrease in the N18 SSEP amplitude after IACP correlated positively to the fraction of no-flow time (p = 0.01).Conclusion: RCP attenuated the rate of decay in SSEP amplitudes during IACP. This suggested that RCP had a measurable physiologic effect on central nervous system function and may increase the time that ACP can be safely interrupted.