A Case of Vigabatrin Induced Symptomatic Visual Field Defect

Vigabatrin (VGB) is one of the most frequently prescribed new anti-epileptic drugs in the world since 1989. It has minimal side effects and fewer drug interactions with other anti-epileptic drugs. Recently, concern of the prevalence and pathophysiology of visual impairment with VGB has been increased since the reports of visual field constriction in patients treated with VGB. We report a 46-year-old man with a visual field defect who has been suffering from complex partial seizures for 29 years. Brain magnetic resonance image (MRI) and electroencephalogram (EEG) were non-specific. The frequency of seizures was about 5 times a month for the past 5 years. VGB, in a dose of 1500 mg/day, was prescribed as an add on drug in addition to carbamazepine. 19 months after VGB treatment, the patient complained of visual dimness especially in the lower half of the visual field. He expressed it as "waving". He had no metabolic derangement. Fundus examination, visual evoked potential, and electroretinogram showed normal findings. A visual field analysis showed a bilateral field defect in the lower half. A follow up visual field analysis, 6 months after the withdrawal of VGB, revealed a slight improvement of visual field defects which were noted without significant clinical improvement. This case implicates that visual field defects due to VGB may be partially reversible.

Title Delayed Central Conduction Time on Brainstem Auditory Evoked Potential Pathway in Diabetic Patients: Functional Origin? Or Structural Origin?

BACKGROUND: It has been well known that absolute and interpeak latencies of brainstem auditory evoked potentials (BAEP) are usually prolonged in diabetics. However, Its etiology is still controversial. We tried to identify whether the cause is structural or metabolic in origin by performing BAEP and brain MRI in the diabetic patients. METHODS: BAEP were performed in both the diabetic patients (DM) group (16 males and 15 females) and the normal control group (25 males and 33 female). A brain MRI was performed in the DM group on those who showed abnormal BAEP and com-pared the results of BAEP of the DM group with those of the control group. RESULTS: 7 patients (22.6%) showed abnor-mal BAEP (male; 6, female; 1, unilateral; 4, bilateral; 3) when abnormal BAEP was defined as being larger than two and a half standard deviations of the control group BAEP results. Two males of the DM group who showed abnormal structural lesions of the pons in their brain MRI were not included in the statistical analysis. The remaining 14 diabetic male patients (mean age: 58.7 +/-9.1 years, mean disease duration: 6.1 +/-4.7 years, mean hemoglobin (Hb) A1C: 7.7 +/- 2.0%) and 15 diabetic female patients (mean age: 60.6 +/-10.8 years, mean disease duration: 5.4 +/-5.1 years, mean HgA1C: 7.8 +/-2.1%) were stastistically analyzed. Interpeak latencies of I-III, III-V, and I-V were found to be signifi-cantly prolonged in the DM group. The prolongation of interpeak latencies of I-III and I-V were found to be signifi-cantly correlated with the disease duration only in the diabetic female patients, but not with age and HbA1c. CONCLUSIONS: These findings suggest that both metabolic derangement and structural lesion contribute to prolonging the central conduction time on BAEP pathway in diabetics.