The clinical significance of the bifid or "W" pattern reversal visual evoked potential

Clinical electrophysiology of the optic nerve and retinal ganglion cells

Clinical electrophysiological assessment of optic nerve and retinal ganglion cell function can be performed using the Pattern Electroretinogram (PERG), Visual Evoked Potential (VEP) and the Photopic Negative Response (PhNR) amongst other more specialised techniques. In this review, we describe these electrophysiological techniques and their application in diseases affecting the optic nerve and retinal ganglion cells with the exception of glaucoma. The disease groups discussed include hereditary, compressive, toxic/nutritional, traumatic, vascular, inflammatory and intracranial causes for optic nerve or retinal ganglion cell dysfunction. The benefits of objective, electrophysiological measurement of the retinal ganglion cells and optic nerve are discussed, as are their applications in clinical diagnosis of disease, determining prognosis, monitoring progression and response to novel therapies.

Abnormal evoked potentials in autoimmune glial fibrillary acidic protein astrocytopathy

Autoimmune GFAP astrocytopathy is a new clinical entity and only a limited number of cases have been reported. Here we report the results of multimodal central conduction studies performed in a case of this disorder.

A 72-year-old woman developed gradual cognitive decline and gait disturbance. A neurological examination revealed moderate amnesia, papilloedema, and pyramidal tract impairment of the bilateral lower limbs. The diagnosis of autoimmune GFAP astrocytopathy was made based on the typical MRI findings of periventricular radial linear gadolinium enhancement in the brain and longitudinally extensive lesions in the spinal cord, and anti-GFAP antibody detected in the cerebrospinal fluid. Somatosensory evoked potentials and transcranial magnetic stimulation studies revealed prolongation of conduction times. Visual evoked potentials showed an unusual W-shaped pattern. To our knowledge, this is the first neurophysiological demonstration of prolonged central conduction times in the autoimmune GFAP astrocytopathy. Further investigations are needed to establish the clinical value the neurophysiological examinations in this disorder.

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A typical case of autoimmune GFAP astrocytopathy showed abnormal evoked potentials.

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Prolonged central conduction times suggest central motor and sensory involvement.

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Abnormal VEPs suggest the involvement of the visual pathway.

Double peaked P1 visual evoked potentials in healthy ageing

OBJECTIVES

To robustly examine the prevalence of the double peaked P1 visual evoked potential in healthy younger and older adult populations.

METHODS

The evoked potentials and spectral power changes to simple visual stimuli of 26 healthy younger (M=20.0 y) and 26 healthy older adults (M=76.0 y) were examined.

RESULTS

Group and individual analyses showed a clear effect of age on P1 morphology and amplitude. Older adults showed significantly lower P1 amplitude and 44% of older adults showed a double peaked P1 compared to 12% of younger adults. Double peaked P1 responses were associated with an increase in spectral power in the gamma range.

CONCLUSIONS

The double peaked P1 may be more prevalent in older adults than previously demonstrated and may represent a de-synchronisation of the cortical sources of the visual P1 in healthy ageing. Increased power in post stimulus gamma in the double peak group may be indicative of compensatory neural processing.

SIGNIFICANCE

Clinically the prevalence of the double peaked P1 may have been underestimated, and its reflectance of demyelinating disease overestimated. Experimentally the results suggest that any investigation of visual processing in older adults must control for early changes in P1 morphology.

The bifid visual evoked potential-normal variant or a sign of demyelination?

OBJECTIVE

To prospectively evaluate the diagnostic significance of bifid VEP at initial presentation.

MATERIALS AND METHODS

A hundred and sixteen patients (46 males and 70 females, age 15-54, mean 28.8), with a clinical suspicion of multiple sclerosis (MS), underwent pattern-shift VEP investigation between 1992 and 1998. They were further followed by clinical, CSF, MRI means for at least 5 years (mean 7.2). Twenty-six patients remained healthy, while 90 developed demyelinating disease (in 71 MS and in 19 optic neuritis was the final diagnosis). Fifty healthy persons (20 males aged 18-51, mean 28.8 and 30 females aged 18-48, mean 26.2) represented the control group. The number of persons with bifid VEP in each group are analyzed.

RESULTS

In the controls one out of 50 exhibited bifid VEP configuration. Of 26 patients with unconfirmed suspicion for MS again one had such responses. Bifid VEP were significantly more frequent in patients with demyelinative pathology (nine out of 90, 10.0%, P (chi-squared) < 0.01).

CONCLUSIONS

Bifid VEP is rarely observed in healthy persons. Its presence should suggest the possibility of demyelinating disease and prompt further investigation and follow-up.

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.

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.