Methyl alcohol (methanol) is a clear, colorless, and flammable liquid produced by the reaction of hydrogen with carbon monoxide or carbon dioxide. Methanol is metabolized in the body to formaldehyde by alcohol dehydrogenase, following which formaldehyde is rapidly converted to formic acid, a metabolite that causes the majority of the toxicity associated with methanol (1). Methanol is highly toxic for humans if ingested. Ingestion of as little as 10 mL can result in complete and permanent visual loss from bilateral optic neuropathy, and 30 mL can be fatal, although the fatal dose is typically 100–125 mL. Toxicity usually occurs from accidental ingestion. For example, in some countries, alcoholic beverages are legally prohibited, and homemade alcoholic drinks containing methanol are a source of toxicity (2).
A variety of substances are used to treat methanol optic neuropathy. Fomepizole has been found to be safe and effective in the treatment of methanol poisoning, often resulting in both resolution of metabolic acidosis and complete restoration of vision. However, it is expensive and not readily available, particularly in developing countries (3).
Ethanol, B-group vitamins, and systemic steroids often are used, but with limited success. In such cases, the final visual acuity is in the range of counting fingers or worse (4).
Erythropoietin is a glycoprotein that stimulates red blood cell differentiation by preventing apoptosis of erythroid progenitors in the bone marrow. It has shown that erythropoietin also has neuroprotective and neuroregenerative properties in the central nervous system (5), and several small case series have documented improvement in vision when used in patients with nonarteritic anterior ischemic optic neuropathy and traumatic optic neuropathy (6,7).
We report 2 patients with methanol-induced toxic optic neuropathy who experienced dramatic visual improvement when they were treated with a combination of intravenous erythropoietin, systemic corticosteroids, vitamins, and folic acid.
A 30-year-old man was referred with a chief complaint of bilateral vision loss. He had no history of systemic disease and took no medications. He had drunk about 100 mL of a homemade alcoholic beverage 3 days previously. Subsequent analysis of the drink revealed that it contained methanol. We later found that 7 people had consumed the same drink, 3 of whom experienced vision loss, leading to complete blindness in 2, 1 of whom was our patient. A third patient died from severe metabolic acidosis despite treatment with hemodialysis and other supportive measures. The other 3 individuals had no visual or systemic deficits.
This patient's visual acuity had begun to decrease within 24 hours after ingestion. At presentation, his vital signs were normal, and he was alert and cooperative. Visual acuity was no light perception (NLP) in both eyes. Pupils were dilated and nonreactive to light. Slit-lamp biomicroscopy revealed no abnormality, and intraocular pressures were normal. Fundus examination revealed mild hyperemic disc swelling bilaterally. Systemic and neurological assessments were unremarkable. Optical coherence tomography (OCT) showed marked thickening of peripapillary retinal nerve fiber layer (RNFL), with average thicknesses of 160 and 171 μm in the right and left eye, respectively (Fig. 1).
The patient was admitted to hospital. Complete blood count, erythrocyte sedimentation rate, and C-reactive protein were within normal limits as was a metabolic panel. The patient's blood methanol concentration was 5 mmol/L (normal, 5–15 mmol/L). Magnetic resonance imaging of the brain and orbits was unremarkable.
The patient was begun on intravenous methylprednisolone (500 mg twice a day) combined with vitamin B12 (100 mg/day), vitamin B6 (100 mg/day), and folic acid (10 mg/day). Because the patient's serum methanol was within the normal range, we chose not to treat him with ethanol. After 2 days, the patient's vision was unchanged. After approval from the ethics committee of the Ophthalmic Research Center and after obtaining written informed consent, the patient was given infusions of 10,000 IU of intravenous erythropoietin twice a day. After the first 2 infusions of erythropoietin, visual acuity improved to 20/200, right eye, and hand movements, left eye. Erythropoietin infusions along with methylprednisolone and vitamins were continued, and 3 days after initiation of erythropoietin, the patient's visual acuity improved to 20/20 in both eyes, pupils were reactive to light, and visual fields were performed (Fig. 2). We continued erythropoietin for 3 days, and methylprednisolone for 5 days, followed by oral prednisolone (1 mg/kg per day) for 2 weeks. Vitamins were given for 1 month. After 3 weeks, the patient's visual acuity remained 20/20 bilaterally, and the optic discs become mildly pale. OCT showed reduction in the peripapillary RNFL compared with pretreatment values, with average thicknesses of 102 and 114 μm in the right eye and left eye, respectively, and visual fields showed significant improvement.
A 35-year-old man was referred 1 week after ingestion of a homemade alcoholic beverage containing methanol. He had experienced 24 hours of unconsciousness and severe acid–base imbalance and had been treated with systemic steroids, intravenous ethanol, hemodialysis, and supportive care. Despite improvement in his general condition, he was noted to have no perception of light in either eye. When he arrived at our hospital, his metabolic panel and blood methanol level were within normal limits. Visual acuity was NLP in both eyes, with moderately dilated pupils that were nonreactive to light stimulation. Slit-lamp biomicroscopy and intraocular pressures were normal, whereas fundus examination revealed mild swelling of both optic discs (Fig. 3).
After obtaining informed consent, the patient was treated with 10,000 IU of intravenous erythropoietin twice a day for 3 days, 500 mg of methylprednisolone twice a day for 5 days (followed by 2 weeks of oral prednisolone [1 mg/kg per day]), vitamin B12 (100 mg/day), vitamin B6 (100 mg/day), and folic acid (10 mg/day) for 1 month. There was no change in the patient's vision over the next 5 days, but 2 weeks later, visual acuity was counting fingers at 6 feet, right eye, and 20/30, left eye. The pupils were sluggishly reactive to light, and the optic discs were pale.
Our 2 patients with methanol optic neuropathy responded dramatically to a combination of intravenous erythropoietin, methylprednisolone, vitamins, and folic acid. The effect of methanol poisoning on the optic nerve is complex. The only fundus lesion observed both ophthalmoscopically and angiographically is optic disc edema because of stasis of axoplasmic flow resulting from the inhibition of oxidative metabolism (8). This axoplasmic slowing appears to occur from swelling of the cytoplasm of the astrocytes and oligodendroglia in the retrolaminar space as well as from compressive obstruction of orthograde axoplasmic flow. The mechanism by which this swelling occurs appears to be a combination of metabolic acidosis and formic acid inhibition of cytochrome C oxidase, resulting in histotoxic hypoxia (9). In addition, methanol can cause central necrosis of the retrolaminar portion of the optic nerve, and necrosis of the basal ganglia, leading to both blindness and acute encephalopathy (10,11). Necrosis of the optic nerves may, in part, be due to alteration in blood flow (11,12).
Although methanol toxicity also leads to retrobulbar demyelination, it is unclear whether this is a primary effect or secondary to axonal damage. Sharpe et al (13) found that optic nerve axons were preserved, yet documented myelin degeneration behind the lamina cribrosa and in cerebral hemispheric white matter.
As in our patient, methanol optic neuropathy causes increased thickness of peripapillary RNFL in the acute phase and diffuse thinning chronically (14). Treatment strategies for methanol optic neuropathy are based on detoxification. Fomepizole, an inhibitor of alcohol dehydrogenase, is very beneficial in treating methanol toxicity, but is not readily available, particularly in developing countries (3). Other treatment protocols, including intravenous ethanol combined with vitamin B1, B6, and B12, have produced variable results (15). High-dose IV corticosteroids often are used, as it is believed that this treatment may inhibit demyelination. Abrishami et al (16) administered high doses of intravenous steroids for 3 days, followed by oral prednisolone (1 mg/kg) for 11 days in 6 patients with vision ranging from 0.93 to 0.86 logarithm of the minimum angle of resolution (logMAR) (equivalent to 20/150–20/160). Three months after treatment, mean visual acuity ranged from 0.33 to 0.2 logMAR (equivalent to 20/30–20/40). In contrast, Fujihara et al (14) found that intravenous methylprednisolone given 6 days after ingestion of methanol was not effective in improving vision (14).
Group B vitamins are thought to decrease the toxic metabolites of methanol, particularly in the brain (17). In one series of 15 patients with methanol optic neuropathy, the combination of steroids, vitamin B12, and folic acid resulted in visual improvement (18).
The ability of erythropoietin to suppress neuronal apoptosis and decrease the inflammatory response has been demonstrated in different models of brain ischemia and inflammation (5). Erythopoietin also has been shown to have beneficial effects on retinal ganglion cells, including reduction in apoptosis and increased survival after experimental optic nerve transaction (19), and in the setting of experimental autoimmune encephalomyelitis, chronically elevated intraocular pressure, and diabetic retinopathy (20,21). This has led to reports of systemic and intravitreal injection of erythropoietin to treat patients with nonarteritic anterior ischemic optic neuropathy and traumatic optic neuropathy with beneficial effects (6,7) and without toxicity (6,22). Erythropoietin is readily available and inexpensive, making it a viable treatment option in developing countries.
We believe that significant vision improvement of our 2 patients is attributable to the additive effect of erythropoietin when combined standard treatments. However, additional studies are needed to determine whether erythropoietin alone or in combination with other therapeutic agents provide optimal visual recovery in patients with methanol optic neuropathy.
The authors thank Neil Miller, MD, for his kind guidance and constant supervision and support in completing this study.
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