Dear Editor, Methanol is a volatile and widely used industrial compound found in cleaning products, antifreeze, and fuel sources, as well as in adulterated alcoholic beverages. Accidental ingestion remains the most frequent route of exposure; however, inhalation absorption has been increasingly reported.1,2 Methanol is readily absorbed through the respiratory tract, particularly during prolonged exposure in enclosed or poorly ventilated environments. Once absorbed, it is metabolized to formate, which inhibits mitochondrial cytochrome C oxidase, leading to cellular hypoxia. Owing to their high metabolic demand and mitochondrial density, retinal ganglion cells and the optic nerve are particularly vulnerable, explaining the severity of optic nerve injury even after non-oral exposure.2 We report a 64-year-old woman who developed profound bilateral vision loss after inhaling methanol vapors. According to the patient’s history, she had been disinfecting a poorly ventilated room using a methanol-containing product for approximately 3 h. Immediately after completing this exposure period, she developed a severe headache and blurred vision, prompting activation of emergency medical services. She arrived at the hospital approximately 1 h later, that is, about 4 h after the beginning of exposure, and already presented with severe bilateral visual impairment. On examination, she was conscious, oriented, and hemodynamically stable. Laboratory tests revealed metabolic acidosis with an elevated anion gap and a methanol concentration of 0.4 g/L. Visual acuity was no light perception in both eyes. Pupils were nonreactive, and fundus examination revealed sharply demarcated, pale optic discs Figure 1. Spectral-domain optical coherence tomography performed approximately 36 h after symptom onset showed relative preservation of the retinal nerve fiber layer with marked ganglion cell layer loss Figure 2.Figure 1: Color fundus photographs obtained approximately 36 h after the onset of visual symptoms, showing sharply demarcated bilateral optic disc pallorFigure 2: Spectral-domain optical coherence tomography obtained approximately 36 h after symptom onset, demonstrating relative preservation of the retinal nerve fiber layer with marked bilateral ganglion cell layer lossMethanol poisoning was diagnosed, and treatment with folic acid, thiamine, pyridoxine, and intravenous bicarbonate was initiated. Alcohol dehydrogenase inhibition and hemodialysis were considered. Fomepizole, the recommended first-line antidote, was initially contemplated but could not be administered because it was not available at our center. Intravenous ethanol was also considered as an alternative alcohol dehydrogenase inhibitor; however, given the patient’s preserved level of consciousness and hemodynamic stability, the improvement of metabolic acidosis after bicarbonate therapy, and the monitoring requirements and potential adverse effects associated with ethanol therapy, it was ultimately not initiated. Hemodialysis was likewise considered. Although current recommendations support extracorporeal treatment in patients with visual symptoms, our patient had no renal failure, a pH of 7.33, and a methanol concentration of approximately 0.4 g/L (~40 mg/dL), and metabolic acidosis improved promptly after supportive treatment. Therefore, after reassessment of the clinical course and biochemical evolution, extracorporeal removal was not ultimately pursued. The differential diagnosis of acute bilateral optic neuropathy includes ischemic, inflammatory, compressive, and hereditary etiologies. These were considered less likely given the abrupt onset, normal inflammatory markers (erythrocyte sedimentation rate and C-reactive protein), normal cranial computed tomography excluding structural lesions, and the presence of high anion gap metabolic acidosis with a measurable methanol concentration, supporting a toxic etiology. Despite adequate management, visual recovery was minimal, improving only to hand motion in the right eye, while the left eye remained with no light perception. At one-year follow-up, no visual recovery was observed. The persistent severe visual impairment resulted in significant functional disability, preventing the patient from returning to her usual occupational activities. Most reported cases of methanol toxicity involve ingestion, but inhalational exposure is an underrecognized and potentially severe route.3 During the COVID-19 pandemic, increased use of disinfectants correlated with more cases of inhalational methanol toxicity.4 Although some consider inhalational exposure less harmful, acute peaks may cause critical damage, as in our case. Awareness of this route of exposure is essential, particularly in poorly ventilated or occupational settings. Treatment with ethanol, folic acid, sodium bicarbonate, and hemodialysis can prevent further toxicity by blocking formic acid formation, but once optic nerve damage occurs, the prognosis remains poor.5 Our case underscores the need for early recognition, prevention, and public education regarding safe use of methanol-containing disinfectants. Ophthalmologists and emergency physicians should maintain a high index of suspicion for methanol intoxication even in the absence of an ingestion history. Prompt identification and systemic management are crucial to minimize irreversible visual loss. Data availability statement The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request. Declaration of ethics patient consent This study was performed in accordance with and conforming to the Declaration of Helsinki. The authors certify that they have obtained all appropriate patient consent form. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest The authors declare that there are no conflicts of interest in this paper.
Alcaide-Costa et al. (Thu,) studied this question.