Delayed and reversible ethambutol optic neuropathy

Abstract

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.

Keywords: Drug toxicity; Ethambutol; Optic neuropathy.

Fig. 1

Funduscopic exam OS and OD showing trace nerve pallor OD > OS in the context ofworsening vision with ethambutol therapy.

Fig. 2

(A) OCT taken for subacute worsening of visual acuity in the context of ethambutol therapy, showing borderline optic nerve thickness OD (79 μm) and full thickness OS (95 μm). (B) Macular ganglion cell layer (GCL) measurements taken during the same visit.

Fig. 3

Thinning of the macular GCL OD was observed from one month post-cessation of ethambutol (above) to three months post-cessation (below).

Fig. 4

Thinning of the optic nerve OD (A, from 73 μm to 67 μm) and OS (B, from 95 to 88 μm) from five months post-cessation of ethambutol to ten months post-cessation.

Fig. 5

Continued thinning of the macular GCL OD (A) and mild thinning of the macular GCL OS (B) from five to ten months post-cessation of ethambutol.