II. Pathophysiology
- Methanol is a common industrial and household solvent (paint remover) and fuel additive
- Antifreeze
- Perfume
- Pain solvents
- Windshield washing fluid
- Mechanisms of ingestion
- Accidental Ingestion by children
- Alcoholism with Methanol ingestion when Alcohol unavailable
- Bootleg Alcohol (especially in developing nations, and where outlawed in conservative countries)
- Industrial workers may inhale Methanol vapors (e.g. formaldehyde production, shellac processing)
- Methanol is quickly absorbed by the gastrointestinal tract
- Serum levels peak within 90 minutes of ingestion
- Hepatic Metabolism
- Methanol is metabolized into Formaldehyde (via Alcohol dehydrogenase)
- Formaldehyde is metabolized into Formic Acid (via aldehyde dehydrogenase)
- Formic acid is the primary toxin resulting in most of the ingestion-related damage and Metabolic Acidosis
- Formic acid is very slowly metabolized into carbon dioxide and water (via Tetrahydrofolate)
III. Symptoms
- Symptom onset is delayed 12-24 hours from ingestion
- Related to delay in metabolism to formic acid
- Neurologic
- Headache
- Altered Level of Consciousness
- Seizure
- Extrapyramidal symptoms
- Parkinsonism
- Paresthesias
- Tinnitus (from Ototoxicity)
- Cardiopulmonary
- Gastrointestinal
- Ocular
- Blurred Vision
- Double Vision
- Progressive Vision Loss
IV. Lab
- Serum Methanol level
- Available at many community hospitals
- Serum Lipase or Serum Amylase
- Metabolic panel
- Decreased serum bicarbonate
- Anion-gap Metabolic Acidosis
- Osmolal Gap
- Hypomagnesemia
- Hypophosphatemia
V. Differential Diagnosis
- See Altered Level of Consciousness
- See Toxic Ingestion
- See Vision Loss
- Ethylene Glycol Toxicity
- Liver failure (hyperammonemia)
- Renal Failure (Uremia)
- Head Injury
- Encephalitis
- Meningitis
VI. Complications
-
Vision Loss
- Formic acid causes Optic Nerve demyelination
- Occurs with serum Methanol levels >20 mg/dl
- Onset of ocular changes within 48 hours of ingestion
-
Parkinsonism
- Methanol and metabolites cause Basal Ganglia damage resulting in Parkinsonian-like signs
- Onset weeks after ingestion
- Hemorrhagic Pancreatitis
- Occurs in more than two thirds of Methanol Poisoning
- Death
- Minimum lethal ingestion: 1 mg/kg
- Even one tbs of 40% Methanol can kill an adult
VII. Management
- Fomepizole (Antizol)
- Start immediately if Methanol toxicity is suspected
- Hemodialysis
VIII. References
- Korabathina in Ramachandran (2012) Methanol Toxicity, EMedicine
- Leikin (1996) Poisoning and Toxicology, Lexi-Comp, Cleveland, p. 957-8
- Swadron and Nordt in Majoewsky (2013) EM:Rap 13(8): 3
