Is visual field constriction in epilepsy patients treated with vigabatrin reversible?

Does the Swedish Interactive Threshold Algorithm (SITA) accurately map visual field loss attributed to vigabatrin?

Background

Vigabatrin (VGB) is an anti-epileptic medication which has been linked to peripheral constriction of the visual field. Documenting the natural history associated with continued VGB exposure is important when making decisions about the risk and benefits associated with the treatment. Due to its speed the Swedish Interactive Threshold Algorithm (SITA) has become the algorithm of choice when carrying out Full Threshold automated static perimetry. SITA uses prior distributions of normal and glaucomatous visual field behaviour to estimate threshold sensitivity. As the abnormal model is based on glaucomatous behaviour this algorithm has not been validated for VGB recipients. We aim to assess the clinical utility of the SITA algorithm for accurately mapping VGB attributed field loss.

Methods

The sample comprised one randomly selected eye of 16 patients diagnosed with epilepsy, exposed to VGB therapy. A clinical diagnosis of VGB attributed visual field loss was documented in 44% of the group. The mean age was 39.3 years ± 14.5 years and the mean deviation was -4.76 dB ±4.34 dB. Each patient was examined with the Full Threshold, SITA Standard and SITA Fast algorithm.

Results

SITA Standard was on average approximately twice as fast (7.6 minutes) and SITA Fast approximately 3 times as fast (4.7 minutes) as examinations completed using the Full Threshold algorithm (15.8 minutes). In the clinical environment, the visual field outcome with both SITA algorithms was equivalent to visual field examination using the Full Threshold algorithm in terms of visual inspection of the grey scale plots , defect area and defect severity.

Conclusions

Our research shows that both SITA algorithms are able to accurately map visual field loss attributed to VGB. As patients diagnosed with epilepsy are often vulnerable to fatigue, the time saving offered by SITA Fast means that this algorithm has a significant advantage for use with VGB recipients.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2415-14-166) contains supplementary material, which is available to authorized users.

Relationship between the area of isopters and Vigabatrin dosage during two years of observation

Background

The aim of the study was to evaluate the relationship between the area of isopters obtained using semi-automated kinetic perimetry (SKP) and Vigabatrin dosage in epilepsy patients with pretreatment baseline examination during 2-years of the follow-up.

Methods

29 epilepsy patients were included into the study, but 15 individuals were excluded due to cognitive impairment, intracranial pathologies or eye diseases. Finally, 14 patients were examined with SKP before VGB treatment and after 6, 12, 18, and 24 months. Reaction time (RT)-corrected areas of three isopters (III4e, I4e and I2e) were measured for each of five examinations and compared intra-individually during 2-years period. Additionally, six epilepsy patients on other antiepileptic drugs were examined five times with SKP as a control.

Results

There was a significant decrease of I2e, I4e and III4e isopters’ area during the follow-up of two years. Correlation was found between the I2e isopter’s area and both cumulative dose and mean daily dose of VGB. With increasing RT, there was decreasing of all isopters’ area in patients receiving VGB. In epilepsy patients who were not receiving VGB, there were no significance differences in isopters’ area during follow-up.

Conclusion

There was attenuation of area of III4e, I4e and I2e isopters obtained with SKP during a period of 2 years. RT, the cumulative dose and the mean daily dose of VGB influenced isopters' area obtained with SKP.

Attenuation of the retinal nerve fibre layer and reduced retinal function assessed by optical coherence tomography and full-field electroretinography in patients exposed to vigabatrin medication

PURPOSE

To investigate the clinical value of assessment of peripapillary retinal nerve fibre layer (RNFL) thickness with OCT in addition to the evaluation of retinal function measured by full-field electroretinography (ff-ERG) in patients with suspected vigabatrin (VGB)-attributed visual field defects.

METHODS

Visual fields from adult patients in our clinical follow-up program for VGB medication were analysed. Twelve patients with suspected VGB-attributed visual field defects were selected for the study. They were re-examined with computerized kinetic perimetry, ff-ERG and OCT (2D circle scan).

RESULTS

Constricted visual fields were found in all patients. Comparative analysis of ff-ERG parameters showed reduced b-wave amplitudes for the isolated and the combined rod and cone responses (p < 0.0001). The a-wave, reflecting photoreceptor activity, was reduced (p = 0.001), as well as the summed amplitude of oscillatory potentials (p = 0.029), corresponding to inner retinal function. OCT measurements demonstrated attenuation of the RNFL in nine of 12 patients, most frequently superiorly and/or inferiorly. No temporal attenuation was found. Significant positive correlations were found between the total averaged RNFL thickness, superior and inferior RNFL thickness and reduced ff-ERG parameters. Positive correlations were also found between RNFL thickness and isopter areas.

CONCLUSION

OCT measurements can detect attenuation of the RNFL in patients exposed to VGB medication. RNFL thickness correlates with reduced ff-ERG parameters and isopter areas of constricted visual fields, indicating that VGB is retino-toxic on several levels, from photoreceptors to ganglion cells. The study also supports previous studies, suggesting that OCT measurement of the RNFL thickness may be of clinical value in monitoring patients on vigabatrin therapy.

Visual field and ocular safety during short-term vigabatrin treatment in cocaine abusers

PURPOSE

To evaluate the ocular safety of short-term vigabatrin treatment of cocaine abuse.

DESIGN

Multicenter, prospective, randomized, placebo-controlled, double-masked, parallel assignment study.

METHODS

Cocaine addicts were randomized to receive vigabatrin 3000 mg/day, cumulative dose 218 g (n = 92), or placebo (n = 94) for 12 weeks. Subjects underwent examination of visual acuity (ETDRS) and peripheral visual field (PVF) by Humphrey Field Analyzer (HFA) 60-4 program before and after treatment. Reliable PVF tests (fixation loss, false positive, and false negative <33%) for 103 subjects were included for the analysis. The threshold visual sensitivity (TVS) was analyzed by points, rings and zones. Main outcome measures included visual acuity decrease by 15 letters and/or significant PVF alteration, defined as 5 or more visual field location points having greater than or equal to 15 dB reduction in TVS or decline (≥33% loss) in posttreatment TVS for 1 or more rings.

RESULTS

Visual acuity decrease was detected in 1 eye of a subject receiving placebo and in none receiving vigabatrin. Posttreatment reduction in TVS more than 15 dB in 5 or more adjacent visual field location points combined with reduction in TVS greater than 33% in 1 or more of the rings was detected in 2 of 54 subjects (3.7%) from the vigabatrin group and in 1 of 49 subjects (2%) from the placebo group (P = .9, NS). None of the PVF changes were bilateral or concentric.

CONCLUSIONS

Short-term use of vigabatrin did not cause a decrease in visual acuity or significant peripheral visual field changes in cocaine abusers.

Visual field loss in patients with refractory partial epilepsy treated with vigabatrin: final results from an open-label, observational, multicentre study

BACKGROUND

Use of the antiepileptic drug vigabatrin is associated with an elevated risk of visual field loss.

OBJECTIVE

To determine the frequency of, and risk factors for, vigabatrin-attributed visual field loss (VAVFL) in the setting of a large-scale, multinational, prospective, observational study.

STUDY DESIGN

A comparative, open-label, parallel-group, multicentre study.

SETTING

Hospital outpatient clinics at 46 centres in five countries.

PATIENTS

734 patients with refractory partial epilepsy, divided into three groups and stratified by age (8-12 years; >12 years) and exposure to vigabatrin. Group I comprised patients treated with vigabatrin for > or =6 months. Group II comprised patients previously treated with vigabatrin for > or =6 months who had withdrawn from the drug for > or =6 months. Group III comprised patients never treated with vigabatrin. Patients underwent perimetry at either 4- or 6-month intervals, for up to 36 months. Visual field outcome was evaluated masked to drug exposure.

INTERVENTION

Perimetry.

MAIN OUTCOME MEASURE

The visual field outcome at each of four analysis points: (i) at enrolment (i.e. baseline, all patients); (ii) for patients exhibiting a conclusive outcome at the initial visual field examination; (iii) for patients exhibiting at least one conclusive outcome to the visual field examinations; and (iv) at the last conclusive outcome to the visual field examinations.

RESULTS

Of the 734 patients, 524 yielded one or more conclusive visual field examinations. For Group I, the frequency of VAVFL at the last conclusive examination was 10/38 (26.3%) for those aged 8-12 years and 65/150 (43.3%) for those aged >12 years. For Group II, the respective frequencies were 7/47 (14.9%) and 37/151 (24.5%). One case resembling VAVFL was present amongst the 186 patients in Group III at the last conclusive examination. The frequency of VAVFL in Groups I and II combined was 20.0% for those aged 8-12 years and 33.9% for those aged >12 years. VAVFL was associated with duration of vigabatrin therapy (odds ratio [OR] up to 15.2; 95% CI 4.4, 51.7), mean daily dose of vigabatrin (OR up to 26.4; 95% CI 2.4, 291.7) and male gender (OR 2.51; 95% CI 1.5, 4.1). VAVFL was more frequently detected with static than with kinetic perimetry (OR up to 0.43; 95% CI 0.24, 0.75).

CONCLUSIONS

Since the probability of VAVFL is positively associated with treatment duration, careful assessment of the risk-benefit ratio of continuing treatment with vigabatrin is recommended in patients currently receiving this drug. All patients continuing to receive vigabatrin should undergo visual field examination at least every 6 months for the duration of treatment. We recommend two-level (three-zone), gradient-adapted, suprathreshold static perimetry of the peripheral field together with threshold perimetry of the central field out to 30 degrees from fixation. The frequency of ophthalmological and perimetric examinations should be increased in the presence of VAVFL.

Justification of vigabatrin administration in West syndrome patients? Warranting a re-consideration for improvement in their quality of life

West syndrome (WS) or infantile spasms (IS) is a severe epileptic syndrome associated with poor prognosis and increased morbidity. The exact etio-pathogenesis of the disorder still remains elusive ant therefore the management continues to pose a challenge to the clinicians. Currently, adreno-corticotrophic hormone (ACTH), steroids and vigabatrin (VGB) form the mainstay of its treatment. However, the recent detection of an irreversible visual field defect observed in as high as 30-50% of children treated with vigabatrin has raised concern over the drug's usage. This brief paper is intended to highlight the significance of the irreversible visual toxicity in an already existent mentally challenged state in WS patients, which can lead to a worsening in the disability status of such patients. Therefore, based on the enhancement of handicap by VGB administration it is recommended that a comprehensive review be performed on its continuation in WS patients in order to prevent further deterioration of their quality of life (QOL).

Treatment of refractory complex partial seizures: role of vigabatrin

Vigabatrin (VGB) is an antiepileptic drug that was designed to inhibit GABA-transaminase, and increase levels of gamma-amino-butyric acid (GABA), a major inhibitory neurotransmitter in the brain. VGB has demonstrated efficacy as an adjunctive antiepileptic drug for refractory complex partial seizures (CPS) and for infantile spasms (IS). This review focuses on its use for complex partial seizures. Although VGB is well tolerated, there have been significant safety concerns about intramyelinic edema and visual field defects. VGB is associated with a risk of developing bilateral concentric visual field defects. Therefore, the use of VGB for complex partial seizures should be limited to those patients with seizures refractory to other treatments. Patients must have baseline and follow-up monitoring of visual fields, early assessment of its efficacy, and ongoing evaluation of the benefits and risks of VGB therapy.

Current role of vigabatrin in infantile spasms

Vigabatrin (VGB), a selective irreversible inhibitor of gamma-aminobutyric acid transaminase, has proved to be effective against cryptogenic and symptomatic infantile spasms (IS). Unfortunately, reports of serious visual field defects have led to a drastic reduction in the use of the drug. This review is based on a systematic search in the literature for evidence regarding efficacy and safety of VGB in IS. Based on a specific mechanism of action, there is a solid evidence of clinical efficacy of VGB in children with Tuberous Sclerosis. Similarly, VGB could represent a potential effective therapy also for spasms due to focal cortical dysplasia. In infants with spasms due to other causes, the risk of ophthalmologic toxicity should be carefully weighted against the benefit of controlling spasms.

Vigabatrin

Refractory epilepsies such as infantile spasms (IS) and complex partial seizures (CPS) can have a severe negative impact on the neurological integrity and quality of life of affected patients, in addition to drastically increasing their risk of premature mortality. Early identification of potentially effective pharmacotherapy agents is important. Vigabatrin has been shown to be a generally well tolerated and effective antiepileptic drug (AED) in a wide variety of seizure types affecting both children and adults, particularly those with IS and CPS. A bilateral, concentric constriction of the peripheral visual field characterizes the visual field defect (VFD) associated with vigabatrin, well characterized by numerous studies. This peripheral VFD presents in 30-50% of patients with exposure of several years; however, most of these patients are asymptomatic. In well-controlled studies, the earliest onset in patients with CPS is 11 months and at 5 months in infants, with average onsets being more than 5 years and 1 year, respectively. Patients with a peripheral VFD retain an average 65 degrees of lateral vision (normal, 90 degrees). The fact that many patients never develop the vigabatrin-related peripheral VFD, despite long-term exposure at high doses, may support the hypothesis that the injury is an idiosyncratic adverse drug reaction (as opposed to a strict dose- or duration-dependent toxicity). Effective testing methods are available to aid in the early detection and management of the peripheral VFD. This article discusses issues of importance to clinical decision-making in the use of vigabatrin to assist the physician and patient in assessing the benefits of vigabatrin therapy and understanding the potential risks of the VFD and uncontrolled seizures.

Retinal function in rabbits does not improve 4-5 months after terminating treatment with vigabatrin

PURPOSE

We have previously reported changes in retinal function and histopathology in rabbits treated with vigabatrin. The purpose of the present study was to evaluate retinal function and histopathology of retina in rabbits 4-5 months after terminating vigabatrin medication.

METHODS

Five rabbits were treated with a daily per oral dose of vigabatrin during 12-13 months. After terminating treatment an observation period of 4-5 months followed. Six rabbits receiving water served as controls. Standardized full-field electroretinograms were performed every 6-8 weeks, using a Burian-Allen bipolar contact lens. After 18 months the rabbits were sacrificed and the morphology of the sectioned retina was studied. The antibodies used for staining were GABA, GFAP, GAD, and vimentin.

RESULTS

After 12-13 months of treatment the full-field ERG was reduced in all rabbits treated with vigabatrin. There was a statistically significant difference in the dark adapted cone b-wave amplitude between treated animals and controls (Wilcoxon signed-rank test, p = 0.043). This difference was consistent also 4-5 months after terminating treatment. Immunohistology of the sectioned retina demonstrated no significant difference in immunoreactivity between treated animals and controls. All treated rabbits demonstrated elevated serum concentration of the drug during medication.

CONCLUSION

Four to five months after terminating treatment with vigabatrin the rabbit full-field ERG remains reduced in isolated cone b-wave amplitude indicating that vigabatrin induced retinal dysfunction may be irreversible. However, immunohistology is normal after a period without treatment, implying that the previously described changes in retinal morphology and glial cell activity are reversible, and probably exist only during treatment.

Vigabatrin and visual field defects in pediatric epilepsy patients

We studied the prevalence, type and severity of vigabatrin (VGB)-attributed visual field defects (VFDs), and used these data to assess the associated risk factors in pediatric patients. Medical records were retrospectively reviewed for 67 pediatric patients who received VGB alone or in combination with other antiepileptic drugs, and who had undergone visual field examinations using a Humphrey visual field analyzer. Of the 67 patients, 15 had VGB-attributed VFDs: 13 had nasal arcuate type, 1 had nasal and temporal constricted type and 1 had nasal constricted type. In terms of severity, 7 patients had Grade I VGB-attributed VFDs, 5 had Grade II, 2 had Grade III, and 1 had Grade IV. Although there were no significant differences between the VFD and non-VFD groups with regards to all tested parameters, there were no cases of VGB-attributed VFDs in patients with total treatment durations <2 yr and cumulative doses <10 g/kg. In conclusion, the prevalence of VGB-attributed VFDs in VGB-treated pediatric epilepsy patients was 22%. The high frequency of VGB-attributed VFDs indicates that physicians should inform all patients of this risk prior to VGB treatment and perform periodic visual field examinations.

[Efficacy and tolerability of vigabatrin in West syndrome]

West syndrome (WS) is a severe epileptic encephalopathy of childhood, characterized by spasms, developmental deterioration and hipsarhythymia.

OBJECTIVE

To evaluate the safety and efficacy of vigabatrin (VGB) in the treatment of WS.

METHOD

We evaluated every patient diagnosed with WS seen at the pediatric epilepsy clinic and exposed to VGB. Patients were interviewed according to a semistructured questionnaire and we analyzed gender, age, etiology (cryptogenic or symptomatic), associated diseases, age of seizure onset, neuroimaging findings, EEG prior and after VGB, use of other antiepileptic drugs, time for seizure control, electroretinogram, visual complaints, adverse events and family history of epilepsy.

RESULTS

Twenty-three patients were evaluated, 16 boys, ages ranging from 1.25 years to 11.5 years (mean=5y3m). Sixteen (69.5%) patients were seizure free, five (22%) had partial seizure control and in two (8.5%) there was no improvement. Only one patient presented gabaergic retinopathy. Six (26%) patients presented adverse events: somnolence, aggressivity or retinopathy. Patients with seizure onset after 6 months of age presented better results after VGB introduction (p<0.05). There was no difference in seizure control according to duration of epilepsy before VGB treatment or etiology of the seizures (p>0.05). After VGB, no patient presented hipsarrhythymia and 50% had a normal EEG.

CONCLUSION

Although VGB may be associated with serious adverse events such as gabaergic retinopathy, our results show that it should be considered in the treatment of WS.

Characterization of vigabatrin-associated optic atrophy

AIMS

To report the discovery of a previously unknown form of optic atrophy associated with use of the anti-epileptic drug vigabatrin.

METHODS

We conducted a retrospective analysis of digitally enhanced ocular fundus photographs, kinetic visual field maps and treatment parameters for 25 patients, who were selected to represent a large spectrum of visual field defects.

RESULTS

In all, 21 patients (84%) evidenced subtle, diffuse atrophy of the retinal nerve fibre layer, in a pattern accessible to scoring. Atrophy scores correlated with visual field remains and cumulative vigabatrin doses. A pathophysiological model is proposed that involves the lengths of intraocular (unmyelinated) retinal ganglion cell axons.

CONCLUSION

Optic atrophy attests to the irreversible nature of vigabatrin's visual toxicity. Ocular fundus imaging should prove useful for objectively monitoring vigabatrin-treated subjects for visual toxicity.