Emergency Medicine · Toxicology
The facts most likely to be tested
Methanol poisoning classically presents with visual disturbances described as blurring of vision or snowfield vision due to retinal toxicity.
Ethylene glycol poisoning is characterized by acute kidney injury resulting from the precipitation of calcium oxalate crystals in the renal tubules.
Both methanol and ethylene glycol ingestion cause a high anion gap metabolic acidosis (HAGMA) with a significantly elevated osmolar gap.
Fomepizole is the first-line antidote that acts as a competitive inhibitor of alcohol dehydrogenase to prevent the formation of toxic metabolites.
Hemodialysis is indicated in patients with severe metabolic acidosis, end-organ damage, or refractory electrolyte abnormalities.
Ethylene glycol ingestion often presents with calcium oxalate monohydrate crystals that appear as envelope-shaped or needle-shaped on urinalysis.
Wood's lamp examination of the urine may show fluorescence in cases of ethylene glycol poisoning due to the presence of fluorescein additives in commercial antifreeze.
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A 45-year-old male is brought to the emergency department by his spouse after being found confused at home. The patient has a history of alcohol use disorder and was recently unemployed. On physical exam, he is tachypneic and appears lethargic. Laboratory studies reveal a pH of 7.15, a bicarbonate of 12 mEq/L, and an anion gap of 24 mEq/L. His serum osmolality is 340 mOsm/kg (calculated 295 mOsm/kg). Urinalysis demonstrates calcium oxalate crystals.
What is the most appropriate next step in management?
Administration of fomepizole
The patient presents with a high anion gap metabolic acidosis and an elevated osmolar gap, highly suggestive of toxic alcohol ingestion; fomepizole is the first-line antidote to inhibit alcohol dehydrogenase.
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Etiology / Epidemiology
Ingestion of methanol (solvents/windshield fluid) or ethylene glycol (antifreeze). High risk in suicide attempts or accidental ingestion by children/alcoholics.
Clinical Manifestations
Methanol causes snowfield vision; ethylene glycol causes calcium oxalate crystal deposition leading to acute renal failure.
Diagnosis
Diagnosis requires anion gap metabolic acidosis and elevated osmolar gap. Serum osmolality is the gold standard for calculating the gap.
Treatment
First-line is fomepizole to inhibit alcohol dehydrogenase. Hemodialysis is indicated for severe acidosis or end-organ damage.
Prognosis
Delayed treatment leads to permanent blindness (methanol) or irreversible renal failure (ethylene glycol).
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Epidemiology & Etiology
Methanol is found in solvents, paint removers, and windshield washer fluid. Ethylene glycol is the primary component of antifreeze. Both are common in intentional overdose or accidental ingestion due to their sweet taste.
Pertinent Anatomy
Metabolism occurs primarily in the liver via alcohol dehydrogenase. Ethylene glycol metabolites target the renal tubules, while methanol metabolites target the retina and optic nerve.
Pathophysiology
Alcohol dehydrogenase converts these alcohols into toxic organic acids (formic acid for methanol; glycolic/oxalic acid for ethylene glycol). This process causes a severe high anion gap metabolic acidosis. The accumulation of calcium oxalate crystals in ethylene glycol poisoning causes direct tubular necrosis.
Clinical Manifestations
Methanol poisoning presents with snowfield vision, blurred vision, and photophobia. Ethylene glycol poisoning is marked by flank pain, hematuria, and oliguria due to renal failure. Both present with altered mental status and Kussmaul breathing as a compensatory mechanism for acidosis.
Diagnosis
Calculate the osmolar gap (measured minus calculated osmolality); a gap >10 mOsm/kg is highly suspicious. Confirm with serum methanol/ethylene glycol levels. Always check urinalysis for envelope-shaped calcium oxalate crystals in ethylene glycol cases.
Treatment
Administer fomepizole immediately to block alcohol dehydrogenase. Ethanol is a second-line alternative if fomepizole is unavailable. Hemodialysis is mandatory for severe metabolic acidosis (pH <7.25), visual changes, or renal failure.
Prognosis
Early intervention is critical to prevent permanent blindness or end-stage renal disease. Patients require serial monitoring of arterial blood gases and serum electrolytes until the anion gap normalizes.
Differential Diagnosis
Diabetic Ketoacidosis: presence of hyperglycemia and ketones
Salicylate toxicity: tinnitus and respiratory alkalosis
Isopropyl alcohol: elevated osmolar gap but NO metabolic acidosis
Lactic acidosis: elevated lactate levels
Uremia: elevated BUN and creatinine without toxic alcohol history