Emergency Medicine Book

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Methanol Poisoning

Aka: Methanol Poisoning, Methanol, Carbinol, Methyl Alcohol, Wood Alcohol, Wood Naptha
  1. Pathophysiology
    1. Methanol is a common industrial and household solvent (paint remover) and fuel additive
      1. Antifreeze
      2. Perfume
      3. Pain solvents
      4. Windshield washing fluid
    2. Mechanisms of ingestion
      1. Accidental Ingestion by children
      2. Alcoholism with Methanol ingestion when Alcohol unavailable
      3. Bootleg Alcohol (especially in developing nations, and where outlawed in conservative countries)
      4. Industrial workers may inhale Methanol vapors (e.g. formaldehyde production, shellac processing)
    3. Methanol is quickly absorbed by the gastrointestinal tract
      1. Serum levels peak within 90 minutes of ingestion
    4. Hepatic Metabolism
      1. Methanol is metabolized into Formaldehyde (via Alcohol dehydrogenase)
      2. Formaldehyde is metabolized into Formic Acid (via aldehyde dehydrogenase)
      3. Formic acid is the primary toxin resulting in most of the ingestion-related damage and Metabolic Acidosis
      4. Formic acid is very slowly metabolized into carbon dioxide and water (via Tetrahydrofolate)
  2. Symptoms
    1. Symptom onset is delayed 12-24 hours from ingestion
      1. Related to delay in metabolism to formic acid
    2. Neurologic
      1. Headache
      2. Altered Level of Consciousness
      3. Seizure
      4. Extrapyramidal symptoms
      5. Parkinsonism
      6. Paresthesias
      7. Tinnitus (from Ototoxicity)
    3. Cardiopulmonary
      1. Dyspnea
      2. Tachypnea
      3. Kussmaul Respirations
      4. Hypotension (or Hypertension)
      5. Bradycardia
    4. Gastrointestinal
      1. Nausea or Vomiting
    5. Ocular
      1. Blurred vision
      2. Double Vision
      3. Progressive Vision Loss
  3. Lab
    1. Serum Methanol level
      1. Available at many community hospitals
    2. Serum Lipase or Serum Amylase
    3. Metabolic panel
      1. Decreased serum bicarbonate
      2. Anion-gap Metabolic Acidosis
      3. Osmolal Gap
      4. Hypomagnesemia
      5. Hypophosphatemia
  4. Differential Diagnosis
    1. See Altered Level of Consciousness
    2. See Toxic Ingestion
    3. See Vision Loss
    4. Ethylene Glycol Toxicity
    5. Liver failure (hyperammonemia)
    6. Renal Failure (Uremia)
    7. Head Injury
    8. Encephalitis
    9. Meningitis
  5. Complications
    1. Vision Loss
      1. Formic acid causes Optic Nerve demyelination
      2. Occurs with serum Methanol levels >20 mg/dl
      3. Onset of ocular changes within 48 hours of ingestion
    2. Parkinsonism
      1. Methanol and metabolites cause Basal Ganglia damage resulting in Parkinsonian-like signs
      2. Onset weeks after ingestion
    3. Hemorrhagic Pancreatitis
      1. Occurs in more than two thirds of Methanol Poisoning
    4. Death
      1. Minimum lethal ingestion: 1 mg/kg
  6. Management
    1. Fomepizole (Antizol)
      1. Start immediately if Methanol toxicity is suspected
    2. Hemodialysis
  7. References
    1. Korabathina in Ramachandran (2012) Methanol Toxicity, EMedicine
    2. Leikin (1996) Poisoning and Toxicology, Lexi-Comp, Cleveland, p. 957-8
    3. Swadron and Nordt in Majoewsky (2013) EM:Rap 13(8): 3

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