Variability on serial testing of pattern reversal visual evoked potential latencies from full-field, half-field and foveal stimulation in control subjects

The use of transcranial magnetic stimulation in diagnosis, prognostication and treatment evaluation in multiple sclerosis

Despite advances in brain imaging which have revolutionised the diagnosis and monitoring of patients with Multiple Sclerosis (MS), current imaging techniques have limitations, including poor correlation with clinical disability and prognosis. There is growing evidence that electrophysiological techniques may provide complementary functional information which can aid in diagnosis, prognostication and perhaps even monitoring of treatment response in patients with MS. Transcranial magnetic stimulation (TMS) is an underutilised technique with potential to assist diagnosis, predict prognosis and provide an objective surrogate marker of clinical progress and treatment response. This review explores the existing body of evidence relating to the use of TMS in patients with MS, outlines the practical aspects and scope of TMS testing and reviews the current evidence relating to the use of TMS in diagnosis, disease classification, prognostication and response to symptomatic and disease-modifying therapies.

Improving test-retest variability of visual-evoked responses in multiple sclerosis: implications for trial design

Remyelination is an important repair strategy in multiple sclerosis. Latencies of visual-evoked responses are a suitable surrogate for remyelination of the optic nerve. Their test-retest variability has been incompletely evaluated, especially in pathologically delayed potentials. Visual-evoked potential was recorded twice, 2.1 +/- 3.1 (mean +/- SD) days apart, in 39 patients with definite or evaluated for multiple sclerosis. Acute optic neuritis and current steroid treatment were exclusion criteria. Mean and difference of the two recordings were calculated for latencies and amplitude, both before and after verification of cursor positioning by a physician blinded for the sequence of recordings. Before verification, the difference between first and second visual-evoked potential was -2.07 +/- 9.07 milliseconds for N75 latency, -1.18 +/- 8.02 milliseconds for P100 latency, and -0.06 +/- 2.71 muV for N75/P100 amplitude (n = 77 eyes, mean +/- SD). Independent verification judged two eyes as unsuitable for analysis. The differences in the remaining 75 eyes were reduced to -1.22 +/- 6.86 milliseconds (N75), -0.7 +/- 3.85 milliseconds (P100) and -0.04 +/- 2.53 microV (amplitude). These effects do not differ between delayed and nondelayed eyes. Similar to magnetic resonance imaging, use of evoked potentials in multiple sclerosis remyelination trials will require independent verification, ideally by a central evaluating facility. Reproducibility should be verified individually at screening.

When do asymmetrical full-field pattern reversal visual evoked potentials indicate visual pathway dysfunction in children?

Our study aimed to find out the association between full-field pattern reversal visual evoked potential (pVEP) transoccipital asymmetries and half-field pVEP transoccipital distributions in children. Over a six-month period, 46 patients (mean age: 9 years 9 months) had both monocular full-field and half-field pVEPs to test checks subtending 50 min of arc in a 35 degree full-field and 0-17.5 degree lateral half-field. Silver-silver chloride electrodes placed at Oz, O1 and O2 were referred to Fz. Monocular full-field data were categorised according to the degree of transoccipital asymmetry. Half-field data were measured and summated to see whether they explained any full-field asymmetry. In this cohort of 46 patients, eight (17%) patients had symmetrically distributed monocular full-field pVEPs for each eye. Four of these patients had normal half-field pVEP distributions for each eye, but the other four showed a half-field deficit in one or both eyes. Of the 38 patients with asymmetrically distributed full-field pVEPs in at least one eye, 17 (44%) patients showed a half-field deficit, 20 (53%) showed responsive, but symmetrically distributed half-field responses, and one patient (3%) showed typical half-field distributions. Half-field pVEPs can help explain full-field asymmetries and should be attempted in any child able to co-operate with testing and in whom visual pathway dysfunction is suspected.

Outcome measures for trials of remyelinating agents in multiple sclerosis: retrospective longitudinal analysis of visual evoked potential latency

Objective

Visual evoked potentials (VEP) may be suitable surrogate outcome measures in multiple sclerosis (MS) remyelination trials. The extent of spontaneous changes of subclinically delayed VEP is unknown, whereas VEP improve after acute optic neuritis (ON).

Methods

In all, 124 patients with three VEP recordings at least 3 months apart: 71 patients with MS who had never suffered clinical ON; 53 patients with ON (isolated ON or ON as an attack of MS at first recording). Latencies of P100 were analyzed by multivariate analysis of variance.

Results

Eyes of patients with MS had a mean P100 latency of 110.2 ms, worsening mildly over time ( n = 104 eyes, P = 0.022). MS patients' eyes with subclinical demyelination (delayed P100 latency at first recording >116 ms) showed no significant evidence of remyelination ( n = 24 eyes, P = 0.27). By contrast, in ON patients' affected eyes, mean P100 latency decreased ( P = 0.001), whereas unaffected eyes remained stable ( P = 0.26). Clinically non-affected eyes from both diagnostic groups with subclinically prolonged latencies remained stable ( n = 32: mean P100 at 124.8 ± 10.7, 123.5 ± 13.6, and 122.8 ± 13.1 ms; P = 0.57), whereas non-affected eyes with normal latency at baseline deteriorated slightly ( P = 0.001). A subgroup with more homogeneously defined follow-up periods confirmed this observation. Non-affected eyes selected for stability (difference <5 ms) between first and second recording deteriorated (normal baseline, n = 66 eyes, P = 0.013) or remained stable (prolonged baseline, n = 18 eyes, 95% confidence interval of change –5.42 to +6.89 ms, P = 0.805).

Conclusion

Prolonged P100 latencies in eyes never affected by clinical ON remain stable and thus can be used as surrogate outcome measure for remyelination trials.

Correlation between full-field and multifocal VEPs in optic neuritis

AIM

To compare performance of multi-focal and full-field Visual Evoked Potentials (VEP) in patients with optic neuritis (ON).

METHOD

26 patients with unilateral ON were enrolled. Multi-focal VEP (MF VEP) was recorded using AccuMaptrade mark system. Four bipolar channels were analysed. Full-field VEP (FF VEP) was performed according to ISCEV standard using ESPION with frontal-occipital electrode placement. Pattern-reversal protocol was implemented with check size of 60' and field of view of 30 degrees .

RESULT

For both tests amplitude and latency of affected eye were statistically different from non-affected eye. The asymmetry of amplitude and latency between two eyes was also very similar for both tests. Averaged Relative Asymmetry Coefficient of amplitude (RAC) for the FF VEP was 0.10 +/- 0.15 and for the MF VEP was 0.12 +/- 0.12 (P = 0.21, paired t-test). Averaged latency difference between affected and non-affected eyes was 13.0 +/- 12 ms for FF and 14.1 +/- 11.1 ms for MF VEPs (P = 0.14, paired t-test). Coefficient of correlation (r) of p100 component of the FF VEP and averaged MF VEP was 0.60 (P < 0.0001) for amplitude and 0.79 (P < 0.0001) for latency. Correlation improved when amplitude and latency asymmetry between two eyes was analysed (r = 0.81 and r = 0.92 respectively). Overall 73% of affected eyes were identified as abnormal by amplitude and/or latency of the FF VEP and 89% was considered abnormal when MF VEP was used. Analysis of individual cases revealed superior performance of MF VEP in detecting small or peripheral defects.

Age-related changes of evoked potentials

The aim of this review is to analyse the current state of our knowledge on evoked potentials (EPs) in ageing and to report some conclusions on the relation between EPs and elder age. Evoked potentials provide a measure of the function of sensory systems that change during the different stages of life. Each sensory system has its own time of maturation. The individuation of the exact period of life when brain ageing starts is difficult to define. Normally, the amplitude of EPs decreases, and their latency increases from adult to elder life. Many authors speculate that these modifications might depend on neuronal loss, changes in cell membrane, composition or senile plaques present in older patients, but there is no evidence that these changes might modify the cerebral function in healthy aged individuals. This review emphasises some incongruities present in different studies confirmed by daily neurophysiologic practice. Different techniques as event-related desynchronization (ERD), contingent negative variation (CNV) and Bereitschaftspotential, are available to study central neuronal changes in normal and pathologic ageing.

Pattern-evoked potential latencies from central and peripheral visual fields

Median P100 and N70 latencies for peripheral field (>8 degrees) TV-generated pattern visual-evoked potentials were 6 and 8 milliseconds less than for central field patterns in subjects with normal pattern visual-evoked potentials. These differences held for patient subgroups with P100 latency maxima from 140 to 100 milliseconds, and for left and right eye data separately compiled. Latencies for central field stimulation exceeded those for peripheral field stimulation in 233 (85%) of 274 eyes for the N70 potential and in 210 (77%) of 274 eyes for the P100 potential. Such data suggest that the faster conducting peripheral visual system, conveying location and motion information, prepares the occipital cortex for the later arriving central data conveying more intricate details.

Serial visual evoked potentials in 90 untreated patients with acute optic neuritis

To establish the value of visual evoked potentials (VEPs) for monitoring disease evolution, we undertook a population-based study of 90 untreated patients 12 to 57 years of age (median, 32 years) at the onset of optic neuritis (ON) and after 2, 4, 12, and 52 weeks. Optic neuritis was monosymptomatic (AMON) in 58 patients and part of the clinically definite multiple sclerosis (CDMS) in 32 patients. The VEP was abnormal in eyes with acute ON in 69 (77%) of 90 patients at onset and in 80 (89%) of 90 patients at one or more of the follow-up sessions. In eyes with acute ON, normalization of an initially abnormal VEP was observed during 1-year follow-up in 13 (19%) of 69 patients. At onset of ON, VEP was abnormal in 35% of the clinically unaffected eyes. By parametric analysis of variance, the latencies (P = 0.0058), the amplitudes (P = 0.0298), and the combined VEP scores (P = 0.0345) in the eyes with acute ON were significantly associated with the time after onset. The latencies were influenced by the presence of CDMS (P = 0.0033), whereas the amplitudes were influenced by visual acuity (P = 0.0000). When visual acuity was included in a multifactor model, the time after onset was, however, not significantly associated with the amplitude (P = 0.8826). The mean latency of the VEPs in eyes with acute ON was significantly shorter in AMON than in ON as part of CDMS. This study provides evidence that VEP abnormality is often transitory, and that VEP often normalizes during follow-up. The diagnostic yield is increased by repeating VEP in the spontaneous course of acute ON. Visual evoked potential is a sensitive tool for revealing subclinical lesions.

Measuring evoked responses in multiple sclerosis

Evoked potentials (EPs) have been widely utilised in Multiple Sclerosis (MS) patients to demonstrate the involvement of sensory and motor pathways. Their diagnostic value is based on the ability to reveal clinically silent lesions and to objectivate the central nervous system damage in patients who complain frequently of vague and indefinite disturbances which frequently occurs in the early phases of the disease. The advent of magnetic resonance imaging (MRI) techniques has greatly reduced the clinical utilisation of EPs, which is not fully justifiable, as the information provided by EPs are quite different from those provided by MRI. The abnormalities of evoked responses reflect the global damage of the evoked nervous pathway and are significantly correlated with the clinical findings, while the vast majority of MRI lesions are not associated to symptoms and signs. Transversal and longitudinal studies have demonstrated that EP changes in MS are more strictly related to disability than MRI lesion burden. On the contrary, MRI is more sensitive than EPs in revealing the disease activity. Evoked responses modifications observed in MS are not disease-specific; moreover longitudinal studies showed latency and morphology changes of evoked responses not always related to clinical changes. Such a dissociation can be explained both by technical factors and by subclinical disease activity. To reduce the negative impact of technical aspects, only reproducible parameters of the evoked responses should be used to monitor disease evolution and therapeutic interventions.

Neurophysiological and cognitive markers of disease evolution in multiple sclerosis

Both evoked potentials and cognitive tests may provide useful information which cannot be derived from the clinical observation. For this reason, there have been some attempts to use EPs in monitoring the natural history of the disease and in assessing the efficacy of therapeutic trials. However, no conclusion can be derived from the few available data. Although MRI is more sensitive than EPs in revealing new lesions in brain, cerebellum and brainstem, EPs are more sensitive in revealing optic nerve and spinal cord lesions. Moreover, the poor relationship between brain MRI abnormalities and disability has raised the possibility that cognitive evaluation may be an additional sensitive marker of brain involvement over time. Since the gold standard for the assessment of disease activity is uncertain, it is therefore advisable that frequent MRI, EPs and cognitive assessment may integrate clinical outcomes measured by conventional scales, both in the study of the natural disease course and in monitoring clinical trials.

Evoked potentials in clinical trials for multiple sclerosis

Multiple sclerosis produces disruption of conduction in the central nervous system by a variety of mechanisms, relating, in part, to loss of the myelin sheath. Although often not well correlated with the clinical course of the disease in individual patients, the resulting evoked potential (EP) disturbances can serve as measures of an accumulating disease burden, particularly in longitudinal population studies. Accordingly, EPs can serve as useful instruments for assessing the effectiveness of therapeutic agents which may alter the course of the multiple sclerosis. Furthermore, since EPs measure conduction within the central nervous system, they provide a means of directly assessing symptomatic treatments designed to improve central conduction.

Normal variability of the amplitude and phase of steady-state VEPs

The present study quantifies the amplitude and phase variability of steady-state VEPs (S-VEPs) and compares this variability between subjects and between individual runs. The S-VEPs were recorded repeatedly in 14 normal subjects with varying spatial and temporal frequencies of sinusoidal gratings; 6 spatial frequencies (range 0.5-8.0 c/deg) with 3 temporal frequencies (4, 6 and 8 Hz) were used. A total of 75 responses were averaged and analyzed by the Fourier method. Four recordings were obtained in each spatio-temporal combination. In general, the phase data showed small inter- and intrasubject variability. As anticipated, the amplitude data showed a large degree of intersubject variability, although the intrasubject variability was very small. In addition, in some stimulus conditions the inter- and intrasubject variability increased, which thus suggested the existence of an optimal spatio-temporal combination. Therefore, these stimulus parameters should be taken into consideration when S-VEPs are applied in clinical practice.

Serial MRI, VEP, SEP and biotesiometry in acute optic neuritis: value of baseline results to predict the development of new lesions at one year follow up

INTRODUCTION

In an attempt to establish the value of MRI, VEP, SEP, and biotesiometry in monitoring disease evolution we undertook a one year follow up study of 70 untreated patients with acute optic neuritis (ON).

MATERIAL & METHODS

ON was monosymptomatic in 48 patients (bilateral in 10) and part of clinically definite multiple sclerosis (CDMS) in 22 patients, examined as mentioned below.

RESULTS

Results are given at onset and at follow up (in brackets). In monosymptomatic ON, brain MRI was abnormal in 53% (53%), VEP in the eye with acute ON in 79% (71%), VEP in the clinically unaffected eye in 34% (47%), SEP in 25% (23%), and biotesiometry in 29% (17%). In CDMS, brain MRI was abnormal in 95% (95%), VEP in the eye with acute ON in 86% (77%), VEP in the clinically unaffected eye in 50% (64%), SEP in 55% (50%), and biotesiometry in 63% (53%). Only minor changes in test scores were observed after one year except for significant improvement of VEP in eyes with acute ON. Eight of 32 patients, characterized by at least one abnormal paraclinical test at onset of monosymptomatic ON, had developed CDMS versus none of 16 patients with normal paraclinical results (p = 0.03; Fisher).

CONCLUSION

Patients with monosymptomatic ON with paraclinical signs of multifocal involvement at onset had an increased risk of developing CDMS. No single test predicted the evolution of CDMS, perhaps due to the relatively short follow up time.

The pattern visual evoked potential. A multicenter study using standardized techniques

The peak latency of the pattern-reversal visual evoked potential is a sensitive measure of conduction delay in the optic nerve caused by demyelination. Despite its clinical utility, the pattern-reversal visual evoked potential has not previously been used in multicenter clinical trials, presumably because of difficulty in standardizing conditions between centers. To establish whether the pattern-reversal visual evoked potential could be adequately standardized for use as a measure in multicenter therapeutic trials for optic neuropathy or multiple sclerosis, stimulus and recording variables were equated at four centers and pattern-reversal visual evoked potentials were recorded from 64 normal subjects and 15 patients with resolved optic neuritis. Results showed equivalent latency and amplitude data from all centers, suggesting that stimulus and recording variables can be satisfactorily standardized for multicenter clinical trials. N70 and P100 peak latencies and N70-P100 interocular amplitude difference were sensitive measures of resolved optic neuritis.

Sequence-dependent deterioration in the visual evoked potential in the absence of drowsiness

When visual evoked potentials (VEPs) are tested patients are often expected to focus on a pattern screen for prolonged periods of time. This may lead to fatigue, failure of concentration and drowsiness, and consequently to a deterioration in the recorded VEP. To determine whether there may be time-dependent changes in the VEP of normal subjects independent of the degree of alertness, attention and altertness were controlled using a reaction time (RT) task in which the subjects were required to re-illuminate the fixation point in the middle of the stimulating screen for the VEP. It was first established that the switching of the fixation point produced little contamination of the background VEP to pattern reversal and that the latency and amplitude of P100 to pattern reversal were identical whether or not the subject was engaged in the RT task. A sequence of 16 averages of the VEP to 256 pattern reversals was recorded, alternately with or without the RT task. The measured RTs decreased during the sequence, presumably due to practice. There was a progressive decrease in the amplitude N70-P100, accompanied by an increase in the variability of the latency of P100. These changes cannot be attributed to lack of alertness, given the improvement in RT. Clinicians should be aware of the possibility of a deterioration in the VEP due to physiological mechanisms when the testing protocol involves multiple averages.

Three-dimensional human pattern visual evoked potentials. II. Multiple sclerosis patients

Pattern visual evoked potentials were obtained from 46 patients with definite relapsing/remitting multiple sclerosis, using both a conventional 5-channel occipital array and a 3-D recording technique consisting of three bipolar derivations approximating the three dimensions of space. These three orthogonal wave forms were displayed as a 3-D Lissajous trajectory for each subject. Two of the 15 patients with completely normal conventional pattern VEPs had abnormalities of the orientation of the B-C curvilinear segment of the 3-D pattern VEPs. Delays in the first major occipital positive component (P100) were evident using both techniques; the correlation between P100 latency and the latency of the corresponding trajectory apex was r = 0.99 (P less than 0.01). Post-chiasmal MRI abnormalities were associated with 3-D VEP orientation abnormalities. Three-dimensional pattern VEPs are moderately more sensitive than conventional pattern VEPs at detecting dysfunction posterior to the optic chiasm in demyelinating disease and do not require the use of eccentric fixation to do so.

Mapped distribution of pattern reversal VEPs to central field and lateral half-field stimuli of different spatial frequencies

Visual evoked potentials (VEPs) to pattern reversal vertical bar stimuli of 3 different sizes (1, 2, 4 c/deg) were recorded from 19 scalp derivations in 50 controls. The stimuli were presented on a full-field (FF) screen of 24 degrees visual angle, and on left and right half-fields (HF) of 12 degrees radius. In 15 controls partial HF stimuli were presented on the central 3 and 6 degrees and as hemiannular stimuli of 12 degrees with occlusion of the central 3 and 6 degrees. An antero-posterior polarity reversal of the N1-P1-N2 sequence was observed for FF VEPs. A tangential polarity reversal was observed for HF VEPs. Also with central or hemiannular stimuli polarity reversals of all VEP components were observed within the scalp. Variants of VEP distribution, absence or prominence of some of the ipsi- or contralateral VEP components were observed in 8-40% of controls. The FF and HF VEP distribution, and the variant VEP asymmetries were partly dependent on the pattern spatial frequency.

Handedness and hemispheric asymmetry of pattern reversal visual-evoked potentials

Pattern reversal visual-evoked potentials (EP) from temporal leads in the two hemispheres of 26 right-handed (14 right-eye-dominant and 12 left-eye-dominant) and 10 left-handed (left-eye-dominant) adults were recorded. Checkerboard patterns (check sizes: 5.7 and 17 min of arc) at 1 and 8 Hz were reversed. Stimuli (a) subtended 6 degrees of visual field, (b) subtended 1 degree of visual field (foveal condition), and (c) were restricted to the annular portion of the visual field around the fovea (peripheral condition). Larger EP amplitudes in right or left hemisphere in relation to handedness, temporal frequency, and visual field condition were recorded. Eye dominance of dextrals appeared to play a role in determining the hemispheric asymmetry. Previous literature data and present results in relation to the hypothesis of different hemispheric specialization for basic visual information are discussed.

The effects of visual field size on hemispheric asymmetry of pattern reversal visual evoked potentials

Visual evoked potentials (VEPs) were recorded in 17 females (10 right-handers and 7 left-handers) and 17 males (10 right-handers and 7 left-handers). The stimulus was a checkerboard pattern phase-reversed at a rate of 1 Hz, binocularly viewed by the subject. Two experimental conditions were tested: field size (the stimulus was enlarged from 1 to 30 degrees of visual angle) and occlusion (the central part of the stimulus was occluded by experimental scotomata of various size--from 1 to 16 degrees). Responses recorded at occipital and temporal leads of the two hemispheres were compared. The P100-N145 amplitude was larger at occipital than at temporal leads, it augmented increasing the size of the stimulus and diminished occluding progressively larger portions of the central field. Hemispheric asymmetries emerged with large field sizes and were not abolished by the presence of experimental scotomata. The hemispheric asymmetry was related to handedness (left-handers had larger amplitudes in the right hemisphere, right-handers in the left hemisphere), but not to sex. Hemispheric asymmetries in VEPs latency were not present. In comparison to males, females showed larger amplitudes and shorter latencies. These results point out that hemispheric asymmetries are found also for the processing of elementary visual stimuli like checkerboards, and they depend both on stimulus parameters (field size) and subject variables (handedness).

Interferon-alpha and transfer factor in the treatment of multiple sclerosis: a double-blind, placebo-controlled trial. AUSTIMS Research Group

The role of interferon-alpha (IFN-alpha) and transfer factor (TF) in the treatment of multiple sclerosis was investigated in a prospective, multi-centric, three year, double-blind, placebo-controlled trial. One hundred and eighty two patients with clinically definite multiple sclerosis were randomised into three treatment groups whose compositions were found to be similar for demographic and prognostic variables including HLA status. Subcutaneous injections of IFN-alpha (3 x 10(6) units), TF (0.5 units) manufactured from leucocytes of cohabiting donors, or placebo were given twice weekly for two months, once weekly for 10 months then fortnightly for 24 months. One hundred and fifty three patients completed the injection regimen. There was no significant difference in the progression of disability for multiple sclerosis patients in either the IFN-alpha or TF-treated groups compared with the placebo group. Similarly, change in visual evoked responses (VER), and in number of oligoclonal bands (OCB) and the level of myelin basic protein (MBP) in the cerebrospinal fluid (CSF) over the trial period did not differ significantly between the three groups. However, the IFN-alpha-treated group had significantly more reported adverse drug reactions and patient withdrawals than either of the other two groups.