A 30 year old presents with nausea, weakness, headache and impaired vision and high anion gap metabolic acidosis. Most likely cause is:
**Core Concept**
Methanol poisoning is a toxic condition caused by the ingestion of methanol, leading to metabolic acidosis, visual impairment, and other systemic complications. Methanol is metabolized to formic acid, which is responsible for the majority of its toxic effects.
**Why the Correct Answer is Right**
Methanol is metabolized by the enzyme alcohol dehydrogenase to formaldehyde, which is then converted to formic acid by aldehyde dehydrogenase. Formic acid interferes with mitochondrial cytochrome c oxidase, leading to cellular respiration impairment and resulting in high anion gap metabolic acidosis, visual disturbances, and other systemic symptoms. The high anion gap is due to the accumulation of formic acid and its metabolites, which are not measured by standard anion gap calculations.
**Why Each Wrong Option is Incorrect**
**Option B:** Ethanol, while also metabolized by alcohol dehydrogenase, does not lead to the same level of toxicity as methanol due to its different metabolic byproducts and the presence of competing enzymes. Ethanol is primarily metabolized to acetaldehyde and then acetate.
**Option C:** Ethylene glycol is another toxic alcohol that can cause metabolic acidosis, but its metabolism leads to the formation of glycolic acid and oxalic acid, which can cause different clinical manifestations such as renal failure and calcium oxalate crystal deposition.
**Option D:** Amphetamine is a central nervous system stimulant that can cause a variety of systemic effects, but it is not typically associated with high anion gap metabolic acidosis or visual disturbances.
**Clinical Pearl / High-Yield Fact**
Methanol poisoning can be treated with fomepizole, a competitive inhibitor of alcohol dehydrogenase, which can help reduce the formation of formic acid and alleviate symptoms. Early recognition and treatment are critical to preventing long-term visual impairment and other complications.
**✓ Correct Answer: A. Methanol. Methanol poisoning is a toxic condition caused by the ingestion of methanol, leading to metabolic acidosis, visual impairment, and other systemic complications.**