Sibling Ethambutol Optic Chiasmopathy

Mitochondrial Mutations in Ethambutol-Induced Optic Neuropathy

Background: Ethambutol-induced optic neuropathy (EON) is a well-recognized ocular complication in patients who take ethambutol as a tuberculosis treatment. The aim of the current study was to investigate the presence of mitochondrial mutations, including OPA1 and Leber's hereditary optic neuropathy (LHON)-mitochondrial DNA (mtDNA), in patients with EON and to determine their effect on clinical features of these patients. Methods: All 47 patients underwent clinical evaluations, including best-corrected visual acuity, fundus examination, and color fundus photography; 37 patients were then followed up over time. Molecular screening methods, including PCR-based sequencing of the OPA1 gene and LHON-mtDNA mutations, together with targeted exome sequencing, were used to detect mutations. Results: We detected 15 OPA1 mutations in 18 patients and two LHON-mtDNA mutations in four patients, for an overall mutation detection rate of 46.8%. The mean presentation age was significantly younger in the patients with the mitochondrial mutations (27.5 years) than in those without mutations (48 years). Fundus examination revealed a greater prevalence of optic disc hyperemia in the patients with mutations (70.5%) than without mutations (48%). Half of the patients with mutations and 91% of the patients without mutations had improved vision. After adjusting for confounders, the logistic regression revealed that the patients with optic disc pallor on the first visit (p = 0.004) or the patients with the mitochondrial mutations (p < 0.001) had a poorer vision prognosis. Conclusion: Our results indicated that carriers with OPA1 mutations might be more vulnerable for the toxicity of EMB to develop EON.

Ethambutol optic neuropathy with correspondent chiasmitis manifestation in magnetic resonance imaging

We present a case of an older patient with toxic chiasmatic optic neuropathy accompanied by bitemporal hemianopia associated with ethambutol use. The patient experienced gradual visual defect recovery that was concurrent with an improvement of chiasmal enhancement in the repeat magnetic resonance imaging performed at his 6-month follow-up. However, his visual field pattern sharply changed to left inferior homonymous quadrantanopia because of a new episode of occipital lobe infarction. After 2 years, the patient's visual function reached the best-corrected visual acuity of 20/20 in both eyes, although he had the sequela of homonymous quadrantanopia related to the infarction. Optical coherence tomography revealed that the loss on the macular ganglion cell–inner plexiform layer was related to retrograde transsynaptic degeneration caused by ethambutol-related chiasmopathy.