Delayed and reversible ethambutol optic neuropathy

PURPOSE: To document an unusual example of ethambutol optic neuropathy developing three years from treatment start date in the absence of renal dysfunction. OBSERVATIONS: The patient, an 82-year-old, 61-kg male undergoing treatment for Mycobacterium Avium Complex, presented with visual acuity that was significantly worse than baseline three years after beginning a treatment regimen which included ethambutol at <15 mg/kg/day. He was also found to have central and paracentral scotomas in both eyes. Ethambutol treatment was immediately halted, and the patient's visual acuity and visual fields improved in the months following. CONCLUSIONS AND IMPORTANCE: It is important to have a high index of suspicion for ethambutol toxicity in any patient on this drug who presents with vision changes consistent with optic neuropathy. The development of ethambutol optic neuropathy can be delayed, and vision loss may be reversible and can continue to improve over months after cessation of therapy.