Abstracts

RATIONALE: Visual field defects (VFDs) are a significant adverse effect reported with the GABAergic AED vigabatrin. VFDs have been reported in up to 50% of patients in small studies, often with asymptomatic clinical presentations not noted for years. VFDs appear to be associated with GABA retinal toxicity. Minimal literature exists regarding the effect of tiagabine, a novel GABA reuptake inhibitor, on visual fields. In light of delayed asymptomatic VFDs with vigabatrin, all cases of potential VFDs secondary to GABAergic AEDs, including tiagabine, should be reported. METHODS: Retrospective chart review of a psychiatric patient receiving adjunctive tiagabine for treatment of bipolar disorder with serial VFs utilizing Allergan Humphrey 120-point Computerized Full Field. RESULTS: The patient responded to adjunctive tiagabine (mean 13.2mg qd, range 4-32mg qd) over 18 months. Humphrey VFs were obtained at 12 months [OD=7/120 absolute defects (AD); OS=1/120 AD] and 18 months [OD=9/120 AD; OS=6/120 AD] at which time tiagabine was discontinued. Post-discontinuation, Humphrey VFs were obtained at 2 months [OD=13/120 AD; OS=11/120 AD], 5 months [OD=7/120 AD; OS=6/120 AD], and 7.5 months [OD=7/120 AD; OS=3/120 AD]. Baseline VEP revealed an abnormal interocular difference of 7.42 milliseconds; repeat VEP was normal with interocular difference of 1.5 milliseconds. MRI with and without gadolinium contrast was normal. Perimacular drusen were noted on neuro-ophthalmologic examination. CONCLUSIONS: Reversible nasal VFDs developed in a patient receiving adjunctive tiagabine. This single case study suggests the potential for tiagabine associated VFDs. Controlled studies are indicated to verify whether this finding was incidental or if tiagabine can cause VFDs.