Vision loss after accidental methanol intoxication: a case report
© Moschos et al.; licensee BioMed Central Ltd. 2013
Received: 18 June 2013
Accepted: 18 November 2013
Published: 20 November 2013
Methanol intoxication is a dangerous situation because it often results in permanent problems such as visual deterioration, metabolic disturbances, neurological dysfunction, and even death. We present, to the best of our knowledge, the first case of irreversible bilateral blindness due to methanol intoxication caused by accidental ingestion of rubbing liquid.
A 49-year-old Greek man developed bilateral irreversible blindness after accidental methanol intoxication. He underwent complete ophthalmological examination, including electroretinogram, visual evoked potentials, multifocal-visual evoked potentials, and optical coherence tomography scan of the optic nerve. Complete laboratory evaluation, urine drug testing, neurological examination, and computed tomography scans were also performed. Visual acuity demonstrated no light perception bilaterally, pupils were semi-dilated and unreactive to light, while the retina was normal in both eyes. Electroretinogram was normal, while visual evoked potentials, multifocal-visual evoked potentials recording, and optical coherence tomography scanning of both optic nerve heads were pathological in both eyes. The neurological examination and the computed tomography scans did not reveal any abnormalities. The laboratory evaluation was normal and the urine drug test was negative for benzodiazepines, opiates, cocaine, amphetamines, salicylates, barbiturates, and phencyclidine.
This is the first case report of methanol intoxication which documents both anatomical and functional abnormalities by means of optical coherence tomography and electrophysiological tests correspondingly. The ocular findings and the reported electrophysiological changes support the hypothesis that methanol affects photoreceptors, Müller cells, and the retrolaminar portion of the optic nerve.
Methanol is a clear, colourless and volatile fluid which smells and tastes like ethanol and therefore it is difficult to differentiate methanol from alcohol. Its main uses are as a raw material for industrial solvents, antifreeze production and in bootleg whiskey. Accidental ingestion of methanol is common (more than half of the methanol intoxication cases), preventable and causes serious side effects. Methanol intoxication (even in small amounts) is very dangerous because it can cause severe visual dysfunction (including irreversible bilateral blindness), metabolic disturbances, permanent neurological dysfunction and even death. We present, to the best of our knowledge, the first case of methanol intoxication caused by accidental ingestion of rubbing liquid.
Neurological examination with the patient awake revealed no extrapyramidal motor disturbances and computed tomography (CT) scans showed no abnormalities. Anion gap was less than 30 mg/dL and no treatment was deemed necessary to initiate. The patient was discharged on the fourth day. He was reexamined one month later. The situation remained unchanged.
Methanol intoxication is followed by a 12–24 hour latency period, after which appear its symptoms and signs which are related to the gastrointestinal, to the ocular, and to the nervous system. Early ocular findings include photophobia, blurred vision, painful eye movements, disturbances of pupil reactions and colour vision, decreased visual acuity, visual field defects and optic disc oedema with tortuous retinal vessels. Their absence on the initial examination is a good prognostic sign and there is not any case reported with permanent visual loss after an initial normal examination. Myelin damage at the retrolaminar optic nerve has been shown in histopathological examination.
In our case, VEPs were almost extinguished and OCT scan of the optic nerve revealed highly decreased values. These findings are in accordance with the literature and are probably a result of the fact that methanol affects photoreceptors, Müller cells, and the retrolaminar portion of the optic nerve.
Methanol intoxication should be early recognised and treated in order to prevent permanent health problems and patient’s death. The treatment includes the treatment of the metabolic acidosis by oral or intravenous bicarbonate administration, the prevention of further oxidation of methanol to toxic metabolites (formaldehyde and formic acid) by competitive inhibition of the enzyme alcohol dehydrogenase (by ethyl alcohol or fomepizole), and the elimination of methanol and its metabolites by haemodialysis.
Our patient developed irreversible blindness bilaterally because he was not treated in the maximum time of two days since the methanol ingestion.
This is the first case report of methanol intoxication which documents both anatomical and functional ocular abnormalities by means of OCT and electrophysiological tests correspondingly. The ocular findings and the reported electrophysiological changes support the hypothesis that methanol affects photoreceptors, Müller cells, and the retrolaminar portion of the optic nerve. It describes a case which has a broader clinical impact across medicine. Our case also underlines the importance of the early recognition and treatment initiation in cases of methanol ingestion.
Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
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