Delayed and reversible ethambutol optic neuropathy.

Area of Science:

• Ophthalmology
• Infectious Diseases
• Pharmacology

Background:

• Ethambutol is a key drug for treating Mycobacterium Avium Complex (MAC).
• Optic neuropathy is a known side effect of ethambutol, typically associated with higher doses or renal impairment.
• Delayed-onset ethambutol optic neuropathy is uncommon.

Observation:

• An 82-year-old male on ethambutol for MAC developed significant vision loss and visual field defects three years into treatment.
• The patient had no renal dysfunction, and ethambutol dosage was below 15 mg/kg/day.
• Ethambutol was discontinued, leading to gradual improvement in visual acuity and visual fields.

Findings:

• This case highlights a rare instance of ethambutol optic neuropathy presenting unusually late in therapy.
• The absence of renal dysfunction underscores that toxicity can occur even in patients with normal kidney function.
• Visual recovery was observed after ethambutol cessation, suggesting reversibility.

Implications:

• Clinicians should maintain a high index of suspicion for ethambutol optic neuropathy in patients with unexplained vision changes, regardless of treatment duration or renal status.
• Delayed diagnosis can be avoided by regular ophthalmological monitoring during ethambutol therapy.
• Prompt discontinuation of ethambutol is crucial for potential vision recovery.