Evoked potentials in clinical medicine (first of two parts)

Neuroaudiological Considerations for the Auditory Brainstem Response and Middle Latency Response Revisited: Back to the Future

The auditory brainstem response (ABR) and middle latency response (MLR) are two sets of evoked potentials that have made major contributions to the field of diagnostic audiology. Many of these contributions were guided by clinical research audiologists. Though many of these auditory evoked potentials (AEPs) are still being used diagnostically by audiologists, there has been a steep decline in their popularity both clinically and in the research laboratory. This is indeed most unfortunate because these AEPs could and should be advancing our field and benefitting many patients. In this article, some critical research is overviewed that addresses some of the reasons why these AEPs (ABR and MLR) are not being utilized as frequently as they should be for neuroauditory assessments. Reflecting on our past when ABR and MLR were more commonly used can serve as a model for our future. Multiple applications and the diagnostic value of these AEPs are presented in an effort to convince audiologists that these electrophysiologic procedures should be revisited and reapplied in the clinic and research settings. It is argued that the dwindling use of ABR and MLR (and AEPs in general) in the field of audiology is not only remarkably premature but also lacks good scientific grounding. While on the other hand, if applied clinically, the value of these AEPs is both substantial and promising.

Misconceptions in IONM Part I: Interleaved Intraoperative Somatosensory Evoked Potential Stimulation

A misconception in the field of intraoperative neurophysiological monitoring (IONM) is that continuous, multi-nerve (four-limb), interleaved somatosensory evoked potential (SSEP) stimulation, while advantageous, is not universally utilized due to variety of misunderstandings regarding this approach to SSEP stimulation. This article addresses the rationale for this misconception. We find that continuous, multi-nerve, interleaved SSEP stimulation is superior to all other stimulation paradigms in most operative scenarios, allowing the fastest acquisition of SSEPs at low stimulation repetition rates, which generate the highest amplitude cortical responses.

A method to assess the default EEG macrostate and its reactivity to stimulation

OBJECTIVE

The default mode network (DMN) is deactivated by stimulation. We aimed to assess the DMN reactivity impairment by routine EEG recordings in stroke patients with impaired consciousness.

METHODS

Binocular light flashes were delivered at 1 Hz in 1-minute epochs, following a 1-minute baseline (PRE). The EEG was decomposed in a series of binary oscillatory macrostates by topographic spectral clustering. The most deactivated macrostate was labeled the default EEG macrostate (DEM). Its reactivity (DER) was quantified as the decrease in DEM occurrence probability during stimulation. A normalized DER index (DERI) was calculated as DER/PRE. The measures were compared between 14 healthy controls and 32 comatose patients under EEG monitoring following an acute stroke.

RESULTS

The DEM was mapped to the posterior DMN hubs. In the patients, these DEM source dipoles were 3-4 times less frequent and were associated with an increased theta activity. Even in a reduced 6-channel montage, a DER below 6.26% corresponding to a DERI below 0.25 could discriminate the patients with sensitivity and specificity well above 80%.

CONCLUSION

The method detected the DMN impairment in post-stroke coma patients.

SIGNIFICANCE

The DEM and its reactivity to stimulation could be useful to monitor the DMN function at bedside.

Flash Visual Evoked Potentials in Conscious Horses: A Preliminary Study

The visual evoked potential (VEP) has many applications in veterinary neurology, but the test is not routinely used in a clinical setting. The aim of this study was to describe a reliable method for recording flash visual evoked potentials (F-VEPs) in nonsedated horses. F-VEPs were recorded from both eyes in 20 healthy and calm, adult horses. Recordings were accomplished without sedation, anaesthesia, or the use of mydriatic drugs. The mean and standard deviation of the latency of the most evident positive peak was 52.76±2.37 ms (P53). The mean latencies of the preceding and following negative peaks were 38.14±4.62 (N38) and 72.35±5.33 ms (N72), respectively. There were 2 mean peak-to-peak amplitudes (N38 - P53 and P53 - N72), and they were 11.85±6.21 and 22.81±11.50 µV, respectively. F-VEP was also recorded from 3 horses (6 eyes) before and during sedation with 2 doses each of xylazine (0.4 and 1.1 mg/kg) or detomidine (0.005 and 0.014 mg/kg). It was possible to obtain a reliable F-VEP with a P53 latency in horses without sedation that was similar to the P2 peak described in previous studies, and these data can be used in the future as a normal reference for comparisons in horses with different diseases using a similar methodology. Sedation affected the results by depressing peak amplitudes and increasing latencies or by completely obscuring any response. The exact impact of sedation on VEPs must be evaluated with much caution due to the small sample size.

Advanced Bioelectrical Signal Processing Methods: Past, Present and Future Approach-Part II: Brain Signals

As it was mentioned in the previous part of this work (Part I)-the advanced signal processing methods are one of the quickest and the most dynamically developing scientific areas of biomedical engineering with their increasing usage in current clinical practice. In this paper, which is a Part II work-various innovative methods for the analysis of brain bioelectrical signals were presented and compared. It also describes both classical and advanced approaches for noise contamination removal such as among the others digital adaptive and non-adaptive filtering, signal decomposition methods based on blind source separation, and wavelet transform.

Lower urinary tract electrical sensory assessment: A systematic review and meta-analysis

Objectives

To summarize the current literature on lower urinary tract electrical sensory assessment (LUTESA), with regard to current perception thresholds (CPTs) and sensory evoked potentials (SEPs), and to discuss the applied methods in terms of technical aspects, confounding factors, and potential for lower urinary tract (LUT) diagnostics.

Methods

The review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) statement. Medline (PubMed), Embase and Scopus were searched on 13 October 2020. Meta‐analyses were performed and methodological qualities of the included studies were defined by assessing risk of bias (RoB) as well as confounding.

Results

After screening 9925 articles, 80 studies (five randomized controlled trials [RCTs] and 75 non‐RCTs) were included, comprising a total of 3732 patients and 692 healthy subjects (HS). Of these studies, 61 investigated CPTs exclusively and 19 reported on SEPs, with or without corresponding CPTs. The recording of LUTCPTs and SEPs was shown to represent a safe and reliable assessment of LUT afferent nerve function in HS and patients. LUTESA demonstrated significant differences in LUT sensitivity between HS and neurological patients, as well as after interventions such as pelvic surgery or drug treatments. Pooled analyses showed that several stimulation variables (e.g. stimulation frequency, location) as well as patient characteristics might affect the main outcome measures of LUTESA (CPTs, SEP latencies, peak‐to‐peak amplitudes, responder rate). RoB and confounding was high in most studies.

Conclusions

Preliminary data show that CPT and SEP recordings are valuable tools to more objectively assess LUT afferent nerve function. LUTESA complements already established diagnostics such as urodynamics, allowing a more comprehensive patient evaluation. The high RoB and confounding rate was related to inconsistency and inaccuracy in reporting rather than the technique itself. LUTESA standardization and well‐designed RCTs are crucial to implement LUTESA as a clinical assessment tool.

A New Apparatus for Recording Evoked Responses to Painful and Non-painful Sensory Stimulation in Freely Moving Mice

Experiments on pain processing in animals face several methodological challenges including the reproducible application of painful stimuli. Ideally, behavioral and physiological correlates of pain should be assessed in freely behaving mice, avoiding stress, fear or behavioral restriction as confounding factors. Moreover, the time of pain-evoked brain activity should be precisely related to the time of stimulation, such that pain-specific neuronal activity can be unambiguously identified. This can be achieved with laser-evoked heat stimuli which are also well established for human pain research. However, laser-evoked neuronal potentials are rarely investigated in awake unrestrained rodents, partially due to the practical difficulties in precisely and reliably targeting and triggering stimulation. In order to facilitate such studies we have developed a versatile stimulation and recording system for freely moving mice. The custom-made apparatus can provide both laser- and mechanical stimuli with simultaneous recording of evoked potentials and behavioral responses. Evoked potentials can be recorded from superficial and deep brain areas showing graded pain responses which correlate with pain-specific behavioral reactions. Non-painful mechanical stimuli can be applied as a control, yielding clearly different electrophysiological and behavioral responses. The apparatus is suited for simultaneous acquisition of precisely timed electrophysiological and behavioral evoked responses in freely moving mice. Besides its application in pain research it may be also useful in other fields of sensory physiology.

A New Recognition Method for the Auditory Evoked Magnetic Fields

Magnetoencephalography (MEG) is a persuasive tool to study the human brain in physiology and psychology. It can be employed to obtain the inference of change between the external environment and the internal psychology, which requires us to recognize different single trial event-related magnetic fields (ERFs) originated from different functional areas of the brain. Current recognition methods for the single trial data are mainly used for event-related potentials (ERPs) in the electroencephalography (EEG). Although the MEG shares the same signal sources with the EEG, much less interference from the other brain tissues may give the MEG an edge in recognition of the ERFs. In this work, we propose a new recognition method for the single trial auditory evoked magnetic fields (AEFs) through enhancing the signal. We find that the signal strength of the single trial AEFs is concentrated in the primary auditory cortex of the temporal lobe, which can be clearly displayed in the 2D images. These 2D images are then recognized by an artificial neural network (ANN) with 100% accuracy, which realizes the automatic recognition for the single trial AEFs. The method not only may be combined with the source estimation algorithm to improve its accuracy but also paves the way for the implementation of the brain-computer interface (BCI) with the MEG.

N2b Reflects the Cognitive Changes in Executive Functioning After Concussion: A Scoping Review

Objectives: The N2b is an event-related potential (ERP) component thought to index higher-order executive function. While the impact of concussion on executive functioning is frequently discussed in the literature, limited research has been done on the role of N2b in evaluating executive functioning in patients with concussion. The aims of this review are to consolidate an understanding of the cognitive functions reflected by the N2b and to account for discrepancies in literature findings regarding the N2b and concussion.

Methods: A scoping review was conducted on studies that used the N2b to measure cognitive functioning in healthy control populations, as well as in people with concussions.

Results: Sixty-six articles that met inclusion criteria demonstrated that the N2b effectively represents stimulus-response conflict management, response selection, and response inhibition. However, the 19 included articles investigating head injury (using terms such as concussion, mild head injury, and mild traumatic brain injury) found widely varied results: some studies found the amplitude of the N2b to be increased in the concussion group, while others found it to be decreased or unchanged.

Conclusion: Based on the available evidence, differences in the amplitude of the N2b have been linked to response selection, conflict, and inhibition deficits in concussion. However, due to large variations in methodology across studies, findings about the directionality of this effect remain inconclusive. The results of this review suggest that future research should be conducted with greater standardization and consistency.

Optimized Measurement Parameters of Sensory Evoked Cortical Potentials to Assess Human Bladder Afferents - A Randomized Study

Overactive bladder and voiding dysfunction are highly prevalent and often associated with malfunction of the bladder afferent pathways. Appropriate diagnostic tools for an objective assessment of afferent nerve function of the human bladder are currently missing. One promising possibility is the assessment of sensory evoked potentials (SEP) during repetitive electrical bladder stimulation, which proved feasible in healthy subjects. For an implementation into clinical practice, however, further refinements for efficient and reliable data acquisition are crucial. The aim of this randomized study was to find the optimal measurement settings regarding stimulation frequency, repetition number, and data acquisition. Forty healthy subjects underwent two visits of SEP (Cz-Fz) assessments using repetitive (500 stimuli) electrical stimulation of 0.5 Hz, 1.1 Hz, and 1.6 Hz and pulse width of 1 ms at the bladder dome or trigone. SEP analyses revealed higher amplitudes and better signal-to-noise ratio (SNR) with lower stimulation frequencies, while latencies remained unchanged. Decreasing amplitudes and SNR were observed with continuing stimulation accompanied by decreasing responder rate (RR). When applying stimuli at a frequency of 0.5 Hz, averaging across 200 stimuli revealed optimal reliability with best SNR, RR and sufficiently high amplitudes. This constitutes an optimal compromise between the duration of the assessment and SEP peak-to-peak amplitudes.

SSEP retains its value as predictor of poor outcome following cardiac arrest in the era of therapeutic hypothermia

OBJECTIVES

To re-evaluate the role of median nerve somatosensory evoked potentials (SSEPs) and bilateral loss of the N20 cortical wave as a predictor of unfavorable outcome in comatose patients following cardiac arrest (CA) in the therapeutic hypothermia (TH) era.

METHODS

Review the results and conclusions drawn from isolated case reports and small series of comatose patients following CA in which the bilateral absence of N20 response has been associated with recovery, and evaluate the proposal that SSEP can no longer be considered a reliable and accurate predictor of unfavorable neurologic outcome.

RESULTS

There are many methodological limitations in those patients reported in the literature with severe post anoxic encephalopathy who recover despite having lost their N20 cortical potential. These limitations include lack of sufficient clinical and neurologic data, severe core body hypothermia, specifics of electrophysiologic testing, technical issues such as background noise artifacts, flawed interpretations sometimes related to interobserver inconsistency, and the extreme variability in interpretation and quality of SSEP analysis among different clinicians and hospitals.

CONCLUSIONS

The absence of the SSEP N20 cortical wave remains one of the most reliable early prognostic tools for identifying unfavorable neurologic outcome in the evaluation of patients with severe anoxic-ischemic encephalopathy whether or not they have been treated with TH. When confounding factors are eliminated the false positive rate (FPR) approaches zero.

Sensory evoked cortical potentials of the lower urinary tract in healthy men

AIMS

To assess the afferent innervation of various locations in the male lower urinary tract (LUT) using sensory evoked cortical potentials (SEPs).

METHODS

Twelve healthy men (mean age: 29.6 ± 7.2 years, mean height: 1.8 ± 0.1 m) underwent repetitive slow (0.5 Hz/1 ms) and fast (3 Hz/0.2 ms) electrical stimulations of bladder (dome/trigone) and urethral (proximal/membranous/distal) locations with simultaneous cortical SEP recording (Cz-Fz). Latencies (ms) and peak-to-peak amplitudes (μV) for SEP components P1, N1, and P2 were analyzed. Tibial SEPs were assessed as methodological control. The reproducibility was investigated from between visits and inter-rater assessments using Bland-Altman plots. Statistical tests comprised analysis of variance (ANOVA), linear regressions, and paired t-tests. Values are given as mean ± standard deviation.

RESULTS

Typical LUTSEPs with P1, N1, and P2 components were successfully detected (100% responder rate) for slow but less successfully for fast stimulation. The slow stimulation provided reproducible LUTSEPs with position specific N1 latencies: dome 125.6 ± 21.3 ms, trigone 122.9 ± 20.5 ms, proximal- 116.1 ± 21.4 ms, membraneous- 118.8 ± 29.3 ms, and distal urethra 108.8 ± 17.8 ms. Despite good inter-rater agreement, latency variability between and within subjects was higher for LUTSEPs than for tibial SEPs. N1 latencies became shorter (P < 0.01) with increasing subject age for bladder dome and distal urethra stimulation.

CONCLUSIONS

LUTSEPs can be successfully obtained for different LUT locations in men using slow electrical stimulation. Location specific differences in N1 latencies may indicate different local afferent innervation. Larger variability of LUTSEPs versus tibial SEPs may be related to the more challenging approach and afferent fibre access within the LUT. Further studies optimizing measurement and analysis approach are required.

Protocol for a prospective, randomized study on neurophysiological assessment of lower urinary tract function in a healthy cohort

Background

Lower urinary tract symptoms are highly prevalent and a large proportion of these symptoms are known to be associated with a dysfunction of the afferent pathways. Diagnostic tools for an objective and reproducible assessment of afferent nerve function of the lower urinary tract are missing. Previous studies showed first feasibility results of sensory evoked potential recordings following electrical stimulation of the lower urinary tract in healthy subjects and patients. Nevertheless, a refinement of the methodology is necessary.

Methods

This study is a prospective, randomized trial conducted at Balgrist University Hospital, Zürich, Switzerland. Ninety healthy subjects (forty females and fifty males) without lower urinary tract symptoms are planned to be included in the study. All subjects will undergo a screening visit (including standardized questionnaires, 3-day bladder diary, urinalysis, medical history taking, vital signs, physical examination, neuro-urological examination) followed by two measurement visits separated by an interval of 3 to 4 weeks. Electrical stimulations (0.5Hz-5Hz, bipolar, square wave, pulse width 1 ms) will be applied using a custom-made transurethral catheter at different locations of the lower urinary tract including bladder dome, trigone, proximal urethra, membranous urethra and distal urethra. Every subject will be randomly stimulated at one specific site of the lower urinary tract. Sensory evoked potentials (SEP) will be recorded using a 64-channel EEG cap. For an SEP segmental work-up we will place additional electrodes on the scalp (Cpz) and above the spine (C2 and L1). Visit two and three will be conducted identically for reliability assessment.

Discussion

The measurement of lower urinary tract SEPs elicited by electrical stimulation at different locations of the lower urinary tract has the potential to serve as a neurophysiological biomarker for lower urinary tract afferent nerve function in patients with lower urinary tract symptoms or disorders. For implementation of such a diagnostic tool into clinical practice, an optimized setup with efficient and reliable measurements and data acquisition is crucial. In addition, normative data from a larger cohort of healthy subjects would provide information on variability, potential confounding factors and cut-off values for investigations in patients with lower urinary tract dysfunction/symptoms.

Trial registration

Clinicaltrials.gov; Identifier: NCT02272309.

Electrophysiological and clinical tests in dry age-related macular degeneration follow-up: differences between mfERG and OCT

BACKGROUND

Age-related macular degeneration (AMD) is one of the major causes of progressive and debilitating visual impairment in developed countries and has become a growing health and social issue that needs to be addressed. Imaging techniques and functional tests are useful to assess the degree of macular dysfunction and AMD progression. However, given the slow progression of the disease, it is necessary to identify which techniques are more sensitive for the diagnosis and monitoring of patients with AMD.

PURPOSE

To study changes observed with both imaging techniques and electrophysiological tests in dry AMD-diagnosed patients during 2 years in order to identify the most sensitive technique.

METHODS

Fundus photography, OCT (macular thickness and number of drusen), Pattern VEP (P100 wave), Pattern ERG (P50 wave) and multifocal ERG (central rings) were carried out in 30 patients that were diagnosed with dry AMD in both eyes. The tests were repeated 1 and 2 years later.

RESULTS

No statistically significant changes were observed in visual acuity or in the severity of the disease throughout the study. OCT showed an increase in the number of drusen, as well as in macular thickness. As for the electrophysiological techniques, no significant changes were observed throughout the study in Pattern VEP or Pattern ERG. mfERG showed significant alterations. Statistical analysis showed that mfERG is more efficient in detecting changes throughout the experimental period.

CONCLUSIONS

OCT and mfERG are useful in the diagnosis and monitoring of dry AMD patients, whilst mfERG is the most sensitive technique to study the progression of this disease in short periods of time.

Evolution of Visual Evoked Potentials in Optic Neuritis

The visual evoked potential (VEP) latency was either abnormally prolonged or absent in the involved eye of 47 patients with optic neuritis. Twenty-two of these patients with known multiple sclerosis (MS), had similar abnormalities to 25 patients with no clinical evidence of MS. Follow-up clinical assessment and VEP were done 10 to 42 (mean 22) months later in 34 patients. In 15 of 34 patients with no VEP from the involved eye during initial examination, 6 returned to normal, 8 had prolonged latencies and 1 still had no response at follow up. Of 19 patients who initially had prolonged latencies in the involved eye, 6 returned to normal, 11 had prolonged latencies and 2 had no response at follow up. The VEP is helpful in confirming the diagnosis of ON. The examination must be performed when the patient is symptomatic or soon thereafter as 35% of our patients with an abnormal initial VEP had a normal VEP at follow up. This normalization was not related to the severity of the initial VEP abnormality.

Changes in neuron-specific enolase are more suitable than its absolute serum levels for the prediction of neurologic outcome in hypothermia-treated patients with out-of-hospital cardiac arrest

BACKGROUND

To determine neurologic outcome in patients with out-of-hospital cardiac arrest (OHCA) and treatment with mild therapeutic hypothermia (MTH).

METHODS

Seventy-three consecutive OHCA patients treated with MTH were retrospectively analyzed. Serum neuron-specific enolase (NSE) was measured 24, 48, and 72 h after admission. In patients with no motor response 48 h after termination of analgosedation (n = 40), clinical neurological examination and evoked potentials (EPs) were determined. Neurological outcome was assessed after 2 months based on the cerebral performance categories (CPC), and categorized as good (CPC 1-3) or poor (CPC 4 and 5).

RESULTS

Forty-three patients had a CPC score of 1-3 and 30 patients had a CPC 4-5. The best predictive value for poor neurologic outcome was an increase of NSE by ≥4.3 ng/mL between day 1 and day 2 (sensitivity 80 %, specificity 100 %, positive predictive value (PPV) 100 %, negative predictive value 86 %). Absolute NSE values were less reliable in the prediction of poor outcome with the highest sensitivity (88 %) and specificity (95 %) if values reached ≥36.3 ng/mL on day 3. Somatosensory EPs (SSEPs) showed a specificity of 100 % and PPV of 100 %; however, sensitivity for evoked potentials was low (29 %). Intriguingly, two initially comatose patients with excessive NSE values (24 h NSE: 101 and 256 ng/mL, and 48 h NSE: 93 and 110 ng/mL, respectively) had physiological SSEPs and regained a CPC score of 1.

CONCLUSION

In patients treated with MTH after OHCA changes in NSE are more suitable than its absolute serum levels for the prediction of poor neurologic outcome. Since unequivocal prediction of poor neurologic outcome is of utmost importance in these patients the decision to limit therapy must be based on several prediction tools with the highest PPV and specificity including SSEPs.

Using biomarkers to predict progression from clinically isolated syndrome to multiple sclerosis

Background

Detection of brain lesions disseminated in space and time by magnetic resonance imaging remains a cornerstone for the diagnosis of clinically definite multiple sclerosis. We have sought to determine if gene expression biomarkers could contribute to the clinical diagnosis of multiple sclerosis.

Methods

We employed expression levels of 30 genes in blood from 199 subjects with multiple sclerosis, 203 subjects with other neurologic disorders, and 114 healthy control subjects to train ratioscore and support vector machine algorithms. Blood samples were obtained from 46 subjects coincident with clinically isolated syndrome who progressed to clinically definite multiple sclerosis determined by conventional methods. Gene expression levels from these subjects were inputted into ratioscore and support vector machine algorithms to determine if these methods also predicted that these subjects would develop multiple sclerosis. Standard calculations of sensitivity and specificity were employed to determine accuracy of these predictions.

Results

Our results demonstrate that ratioscore and support vector machine methods employing input gene transcript levels in blood can accurately identify subjects with clinically isolated syndrome that will progress to multiple sclerosis.

Conclusions

We conclude these approaches may be useful to predict progression from clinically isolated syndrome to multiple sclerosis.

Unilateral cerebral ischemia inhibits optomotor responses of the ipsilateral eye in mice

A reduction in blood flow to the brain causes stroke and damage to neuronal networks. Cerebral ischemia is frequently associated with loss of visual functions. Because retinal and small cerebral vessels are vulnerable to similar risk factors, the loss of vision could result from concurrent retinal ischemia, and it is not clear if visual functions may be inhibited by cerebral ischemia directly. In this study, the distal middle cerebral artery in the right hemisphere of mice was occluded to produce unilateral cerebral ischemia and subsequent infarction. The layer V neurons expressing YFP in transgenic yellow fluorescent protein in transgenic B6.Cg-Tg(Thy1-YFPH)2Jrs/J mice disappeared in the motor and somatosensory cortex, but not in the visual area. The latencies of flash visual evoked potential recorded from two hemispheres were imbalanced, but did not differ markedly from the latencies recorded in controls. However, the optomotor responses of the ipsilateral eye were significantly reduced by 48 h after occlusion. Our results suggest that focused cerebral ischemia may inhibit ipsilateral eye movement in the absence of damage to the visual cortex. This study may provide a platform for further investigation of the relationship between cortical ischemia and visual function.

Prognostic value of electroencephalography and evoked potentials in the early course of malignant middle cerebral artery infarction

Space-occupying brain edema may lead to a malignant course in patients with large middle cerebral artery infarction. Decompressive hemicraniectomy has to be initiated early to prevent further tissue damage. In this retrospective study, we analyzed electroencephalography (EEG) and evoked potentials (EPs), obtained within 24 h after onset of stroke, in 22 patients suffering from a large middle cerebral artery infarction. Our findings indicate a prognostic value of EEG and brainstem auditory EP (BAEP): the absence of delta activity and the presence of theta and fast beta frequencies within EEG-focus predicted a non-malignant course. In contrast, diffuse generalized slowing and slow delta activity in the ischemic hemisphere pointed to a malignant course. Likewise, pathological BAEP were correlated with a malignant course. The coexistence of background slowing and pathological BAEP showed the highest level of significance. In conclusion, our findings implicate an additional early application of electrophysiological methods in stroke patients. EEG and EP deliver useful information to select those patients who develop malignant edema.

Measurement of somatosensory-evoked potential to evaluate function of the trigeminal nerve after rapid palatal expansion treatment in a rabbit model

OBJECTIVE

The aim of this study was to evaluate whether high force or stress response occurs in rapid palatal expansion (RPE) on the skull base would affect the function of trigeminal nerve and its branches by measuring trigeminal somatosensory-evoked potential (TSEP).

STUDY DESIGN

Twenty-four male New Zealand white rabbits were selected when they were 12-13 weeks old with mean weight around 3.05 ± 0.33 kg. A modified acrylic-bonded RPE appliance was used as an expansion tool. Through a series of TSEP measurements performed before the expansion treatment (T0), on the third day of the expansion (T1), at the end of the expansion process (T2), and after 10 days of retention (T3), function of the trigeminal nerve was analyzed with statistical models, including the Kruskal-Wallis test and paired t tests.

RESULTS

A stable short-latency response represented by a "W" waveform was consistently identified on the TSEP spectram analysis. Within-subject comparisons between the experimental group and control group did not show significant differences on TSEP of maxillary nerve and of mandibular nerve.

CONCLUSIONS

TSEP is a valuable technique for a comprehensive evaluation of the trigeminal system. Our study demonstrates that rapid palatal expansion is a safe orthopedic method regarding function of the trigeminal nerve during expansion and short-term retention period in young rabbits.

Visual evoked potentials and MBP gene expression imply endogenous myelin repair in adult rat optic nerve and chiasm following local lysolecithin induced demyelination

Multiple sclerosis (MS) patients may suffer from optic disturbances. Toxin-induced demyelinations have frequently been developed to investigate the cellular and structural aspects of demyelination and remyelination processes, separately. The present study describes functional consequence of lysolecithin (LPC)-induced lesion in the adult rat optic nerves and chiasm by recording the visual evoked potentials (VEPs) from the visual cortex and its correlation with myelin basic protein (MBP) expression in lesion site. Records of VEP were obtained at 2, 7, 14 and 28 days post-injection. We observed that the VEPs generated by light stimuli progressively changed in both amplitude and latency after the lesion as well as in comparison with those generated in control animals. These observations were confirmed through measurement of mRNA expression level for MBP which is one of the important genes expressed in mature oligodendrocytes and Schwann cells. The level of MBP mRNAs in demyelinated chiasm and optic nerves decreased following lysolecithin injection with its least value on day 7, and then it increased to the control level 14 days post-lesion. However, it continued to increase even after that and reached a maximum level 28 days post lesion. Results of the present paper show that, LPC injection in the chiasm share functional and molecular alterations which are found in demyelinating disorders in both the optic nerves and chiasm and also these alterations were coming back to level of control animal on 28 days post lesion, which is typically seen in myelin repair process. The present paper provides new insights into the experimental toxin-induced models that may be useful for evaluating the functional recovery of demyelinated optic nerves and chiasm following various repairing strategies. It also seems to be useful for studying the protective or remyelinating effects of different therapies in e.g. optic apparatus which is more affected by MS.

Conversion paralysis after surgery for lumbar disc herniation

OBJECTIVE

New neurologic deficit after spinal surgery is a rare complication that must be promptly diagnosed and treated to reduce the risk of permanent neurologic disability.

SUMMARY OF BACKGROUND DATA

A 37-year-old woman underwent left laminotomy and L5-S1 diskectomy for the treatment of L5-S1 disc herniation. She was found to be normal after recovery from anesthesia but loss of muscle power in the left lower limb after 1 h.

METHODS

Surgical exploration was performed; no obvious hemorrhage or compression because of hematoma was observed. After the exploration, the muscle power recovered but deteriorated after 10 h.

RESULTS

Re-exploration did not yield any specific findings. In view of the normal electrophysiological and anatomic findings, a psychiatric evaluation confirmed the diagnosis of conversion paralysis with major depression disorder.

CONCLUSION

Normal somatosensory-evoked potentials or motor-evoked potentials in a patient denying sensation of stimuli offer objective evidence of the psychogenic nature of the para/tetraplegia. This report describes a case in which psychopathology interfered with the outcome of a frequently used procedure for a well-defined, chronic, painful condition.

Neurological complications of ankylosing spondylitis: neurophysiological assessment

Studies examined the neurological involvement of ankylosing spondylitis (AS) are limited. This study aimed to assess the frequency of myelopathy, radiculopathy and myopathy in AS correlating them to the clinical, radiological and laboratory parameters. Included were 24 patients with AS. Axial status was assessed using bath ankylosing spondylitis metrology index (BASMI). Patients underwent (a) standard cervical and lumbar spine and sacroiliac joint radiography, (b) somatosensory (SSEP) and magnetic motor (MEP) evoked potentials of upper and lower limbs, (c) electromyography (EMG) of trapezius and supraspinatus muscles. Patients' mean age and duration of illness were 36 and 5.99 years. Bath ankylosing spondylitis metrology index mean score was 4.6. Twenty-five percent (n = 6) of patients had neurological manifestations, 8.3% of them had myelopathy and 16.7% had radiculopathy. Ossification of the posterior (OPLL) and anterior (OALL) longitudinal ligaments were found in 8.3% (n = 2) and 4.2% (n = 1). About 70.8% (n = 17) had >or=1 neurophysiological test abnormalities. Twelve patients (50%) had SSEP abnormalities, seven had prolonged central conduction time (CCT) of median and/or ulnar nerves suggesting cervical myelopathy. Six had delayed peripheral or root latencies at Erb's or interpeak latency (Erb's-C5) suggesting radiculopathy. Motor evoked potentials was abnormal in 54% (n = 13). Twelve (50%) and five (20.8%) patients had abnormal MEP of upper limbs and lower limbs, respectively. About 50% (n = 12) had myopathic features of trapezius and supraspinatus muscles. Only 8.3% (n = 2) had neuropathic features. We concluded that subclinical neurological complications are frequent in AS compared to clinically manifest complications. Somatosensory evoked potential and MEP are useful to identify AS patients prone to develop neurological complications.

Ischemic orbital compartment syndrome after posterior spinal surgery

STUDY DESIGN

Case report.

OBJECTIVE

To describe a patient with ischemic orbital compartment syndrome after undergoing spinal surgery in a prone position.

SUMMARY OF BACKGROUND DATA

Ocular complications after nonocular surgery are devastating. The most common etiology is ischemic optic neuropathy. Orbital compartment syndrome with ischemic change is quite rare and urgent management is necessary.

METHODS

Early diagnosis and surgical intervention was performed for ischemic compartment syndrome after posterior spinal surgery was done.

RESULTS

Despite immediate management, the patient remained blind and ptotic 3 months after the injury.

CONCLUSION

Understanding ocular complications after spinal surgery is vital. Although rare, but the most troublesome complication is ischemic orbital compartment syndrome.

Maternal dietary omega fatty acid intake and auditory brainstem-evoked potentials in Mexican infants born at term: cluster analysis

OBJECTIVE

To identify biological and socioeconomic factors associated with the neurological development of Mexican infants born at term, as measured by brainstem auditory-evoked potentials (BAEPs).

SUBJECTS AND METHODS

We conducted a cohort study among 76 women with low risk pregnancies recruited in their third trimester of pregnancy and followed their infants until 12 months of age. BAEP tests were conducted on the infants before 3 months of age during physiologic sleep, using 100 msec bipolar clicks. Maternal dietary intake was evaluated by food frequency questionnaire. Two BAEP groups (short latency, long latency) were identified by cluster analysis. The association between BAEP group and maternal PUFAs was estimated using logistic regression models adjusted for socioeconomic and biological factors.

RESULTS

Short latency BAEPs were associated with a maternal diet rich in arachidonic acid (OR=3.63, 95% CI 1.23-10.67) after adjusting for age (in days) sex, head circumference and gestational age but was not significantly associated to a maternal diet rich in docosahexaenoic acid (DHA).

CONCLUSIONS

Our results suggest the importance of arachidonic acid intake during pregnancy for short latency BAEPs and adequate fetal myelination.

Initial and Serial Evoked Potentials in Cerebrovascular Critical Care Patients

Results of somatosensory evoked potential (SEP) and brainstem auditory evoked potential (BAEP) examinations performed early in the clinical course of patients with acute cerebrovascular disease correlate statistically significantly with outcome regardless of type and localization of the primary lesion. The prognostic value of serial examinations of SEP and BAEP has not been studied yet. The authors examined a group of 215 patients suffering from acute stroke requiring neurocritical care composed of 75 supratentorial and 36 infratentorial ischemic strokes, 58 supratentorial and 18 infratentorial hemorrhages, and 28 aneurysmatic subarachnoid hemorrhages prospectively using spinal and cortical SEP and BAEP according to routine procedures on admission as well as after 1 and 2 weeks. The findings were correlated to outcome at 4 weeks. Statistical assessment was performed using standard methods of contingency analysis. In all groups, SEP findings were significantly correlated with outcome at initial and all subsequent examinations, similar correlations were also found for BAEP. However, after partialling out the prognostic information gained from the initial examination of SEP and BAEP, the follow-up examinations rendered only a marginal increase in prognostic information. Therefore, the initial examination of evoked potentials supplies valuable prognostic information, however, serial examinations of evoked potentials during the first weeks of disease improve the prognostic information only marginally.

Anesthetic Management for Pediatric Spinal Fusion: Implications of Advances in Spinal Cord Monitoring

Currently, the detection of emerging injury through intraoperative neurologic monitoring is the best way to prevent neurologic injury. This requires a team approach that includes the anesthesiologist, neurophysiologist, and surgeon. The monitoring modalities available for the patient must be considered in planning the anesthetic management. In addition, intraoperative care for the patient requires an ongoing attention to how the anesthetic drugs affect spinal cord monitoring.

Cerebral dysfunction in type 1 diabetes: effects of insulin, vascular risk factors and blood-glucose levels

Type 1 diabetes can lead to several well-described complications such as retinopathy, nephropathy and peripheral neuropathy. Evidence is accumulating that it is also associated with gradually developing end-organ damage in the central nervous system. This relatively unknown complication can be referred to as "diabetic encephalopathy" and is characterised by electrophysiological and neuroradiological changes, such as delayed latencies of evoked potentials, modest cerebral atrophy and (periventricular) white matter lesions. Furthermore, individuals with type 1 diabetes may show performance deficits in a wide range of cognitive domains. The exact mechanisms underlying this diabetic encephalopathy are only partially known. Chronic metabolic and vascular changes appear to play an important role. Interestingly, the differences in the "cognitive profile" between type 1 and type 2 diabetes also suggest a critical role for disturbances of insulin action in the central nervous system.

Reliable and convenient method for the fixation of recording electrodes on nonshaved scalp for intraoperative electrophysiological monitoring: technical note

BACKGROUND

Difficulties with the intraoperative monitoring of evoked responses sometimes occur because of displacement or dislodgment of the recording electrodes during surgery, especially if placed on nonshaved scalp.

METHODS

An alternative fixation method of the recording electrode on the nonshaved scalp was developed. The sterile subdermal needle electrode was attached on the scalp by application of a transparent dressing (Tegaderm) over the electrode followed by fixing with a skin stapler.

RESULTS

The needle electrodes were easily, quickly, and firmly positioned even on the nonshaved scalp. The responses of the intraoperative evoked potentials were highly stable and reproducible throughout the operation.

CONCLUSION

This fixation method for subdermal needle electrodes on the scalp is safe, reliable, and convenient for intraoperative electrophysiological monitoring of evoked potentials, even if the scalp is not shaved.

Examination of nasopharyngeal and tracheal somatosensory evoked potential recordings in dogs

OBJECTIVE

To investigate the value of nasopharyngeal and tracheal recordings of somatosensory evoked potentials (SSEP) in anesthetized dogs.

ANIMALS

10 healthy mixed-breed dogs (5 males and 5 females).

PROCEDURE

Square-ware electrical stimuli (50 microseconds duration, 4Hz) were delivered through bipolar surface electrodes to the median nerve of the right forelimb with 7 to 12 mA constant current. The SSEP were recorded with soft electrodes placed on the epipharynx and dorsal wall of the trachea, respectively. Traditional scalp and neck recordings of SSEP were also performed, using SC-inserted needle electrodes. The potentials recorded dorsally and ventrally from the neuraxis were compared to assess the application of these signals for intraoperative neurophysiologic monitoring.

RESULTS

Electrical stimulation of the median nerve resulted in multiphasic potentials recorded from all 4 recording sites. Latency and phase shifts were observed between the far-field potentials placed ventrally and dorsally from the neuraxis.

CONCLUSIONS AND CLINICAL RELEVANCE

Potentials recorded with nasopharyngeal and tracheal electrodes are regarded suitable for intraoperative neurophysiologic monitoring in anesthized dogs.

Psychogenic paraplegia in a patient with normal electrophysiologic findings

STUDY DESIGN

A case report of psychogenic paraplegia following a motor vehicle accident was clinically diagnosed using median (MN) and posterior tibial nerves (PTN) somatosensory evoked potentials (SSEPs).

OBJECTIVE

To report an unusual case of paraplegia in spite of normal electrophysiological and non-compromising radiographic spine findings.

SUMMARY OF BACKGROUND DATA

Conversion disorder with motor system symptoms or deficit is a subtype which includes symptoms such as impaired motor coordination or balance, paraplegia, muscle weakness, difficulty in swallowing, and urinary retention.

METHODS

The SSEPs were performed by each PTN at the ankle region behind the medial malleolus or the MN at the wrist using square wave pulses in 15 mA intensity. The SSEPs revealed well-developed somatosensory peaks for all extremities.

RESULTS

Well-resolved MN-SSEPs were seen with stimulation of either arm. The principal peaks of N20 and P22 were 17 and 21 ms for both upper extremities. The principal peaks of P37 and N45 were 35 and 46 ms for both lower extremities. No side-to-side latency difference was noted. The MRI scan finding was a non-displaced L1 fracture without spinal canal compromise.

CONCLUSIONS

In spite of an apparent paraplegia, contradictory clinical findings, normal neurophysiologic tests, and normal neuroradiologic findings are positive criteria for paraplegia/quadriplegia with psychogenic etiology.

Afferent vagal modulation. Clinical studies of visceral sensory input

The frequency composition of a continuous time series of R-R intervals may be viewed as the phasic output of a central processing system intimately dependent on sensory input from a variety of afferent sources. While different measures of heart rate variability permit a glimpse into the autonomic efferent limb of this complex system, direct access of afferent fibers in humans has remained elusive. Using a specially designed esophageal catheter/manometer probe, we have been able to gain access to vagal afferent fibers in the distal esophagus. Our studies on the effect of vagal afferent electrostimulation on both cerebral evoked potentials (EvP) and the power spectrum of heart rate variability have yielded the following observations: 1. Stimulation of esophageal vagal afferents dramatically and reproducibly increases the high frequency (HF) vagal power and reduces the low frequency (LF) power of the heart rate autospectrum. 2. This effect is constant across stimulation frequencies from 0.1 to 1.0 Hz and across stimulation intensities from 2.5 to 20 mA. 3. Regardless of the stimulation parameters, there are only minimal changes in heart rate (2-6 bpm) and no change in respiratory frequency. 4. There is a linear correlation between electrical stimulation intensity and the amplitude of cerebral evoked potentials, whereas there is a non-linear relationship with all short-term power spectral indices. 5. While cerebral evoked potentials are only elicited at stimulation intensities above perception threshold, there is already a significant shift to increased vagal efferent modulation well below perception threshold.

CONCLUSION

These studies support the concept that power spectral indices of heart rate variability represent phasic output responses to tonic afferent viscerosensory signals in humans. These studies also demonstrate the feasibility of accessing vagal afferents in humans.

Serial evoked potentials and outcome in cerebrovascular critical care patients

Median-nerve evoked somatosensory evoked potentials (SEPs) and brainstem auditory evoked potentials (BAEPs), examined early in the course of patients suffering from cerebrovascular disease, correlate statistically significantly with outcome. Little is known about the changes of evoked potentials in the course of disease and their correlation to outcome. In a series of 215 patients (75 supratentorial infarctions, 36 infratentorial infarctions, 58 supratentorial hemorrhages, 18 infratentorial hemorrhages, and 28 aneurysmatic subarachnoid hemorrhages) requiring neurologic intensive care treatment, we prospectively examined the correlation between the findings of serial SEPs and BAEPs and outcome at 4 weeks. Evoked potentials were examined after admission, after 1 week, and after 2 weeks. The findings were classified in 4 categories (normal, unilateral or bilateral pathologic findings, unilaterally attenuated, and bilaterally attenuated). Clinical outcome was determined by classification according to the Glasgow Outcome Scale (death, persistent vegetative state, severely incapacitated, mildly incapacitated, and recovery). Statistical evaluation was performed using Fisher's exact test for all variables. In all subgroups, SEPs correlated statistically significantly with outcome at all three examinations. No correlation was found for BAEPs at first examination in infratentorial disease, nor at second examination in subarachnoid hemorrhages. In all other cases, SEPs and BAEPs were correlated statistically significantly with outcome at all three examination timepoints.

Evoked potential monitoring in anaesthesia and analgesia

Electrophysiological monitoring of selected neural pathways of the brain, brainstem, spinal cord and peripheral nervous system has become mandatory in some surgery of the nervous system where preventable neural injury can occur. Evoked potentials are relatively simple methods of testing the integrity of various aspects of the nervous system. This review covers the variety of evoked potentials that can be monitored and outlines the principles of their measurement. Their use in specific situations and how factors such as anaesthesia might affect them is presented.