Ethambutol-induced optic neuropathy in renal disorder: a clinico-electrophysiological study.

Objective: To report the spectrum of ethambutol induced optic neuropathy in a group of renal patients with tuberculosis and the role of visual evoked response (VER) in evaluating this disorder.

Methods: Twenty-three renal patients who were started on ethambutol as a part of anti-tubercular treatment for tuberculosis in India, were divided into 4 groups based on glomerular filtration rate (GFR): group 1-chronic kidney disease (CKD) with GFR < 10 mL/min; group 2-CKD with GFR 10-30 mL/min; group 3-GFR > 30 ≤ 60 mL/min; and group 4-GFR > 60 < 90 mL/min. Detailed clinical and electrophysiological (VER) examinations were carried out in all patients before starting the treatment with ethambutol and at a 3-month interval. Twenty healthy subjects formed the control group.

Results: Ethambutol optic neuropathy developed in 6 (26%) patients with higher incidence (40%) in end-stage renal disease (group 1: CKD on dialysis). Vision was recovered in 4 cases on stoppage of ethambutol, whereas 2 patients (group 1: CKD on dialysis) developed bilateral severe irreversible visual loss and also had associated hepatic dysfunction. Three patients of ethambutol optic neuropathy showed increased latency in VER recording prior to visual loss and 1 patient showed demyelinating lesions in both optic nerves and optic radiation.

Conclusions: Ethambutol should be avoided in renal disorder patients in view of the high incidence of toxic optic neuropathy. Follow-up VER can detect sub-clinical ethambutol toxicity and would be useful for early diagnosis of optic neuropathy.