A Drink to Die From Part.1
High Yield Review - Methanol Toxicity
Case: A 43 y/o male from the Ozarks who is acting "weird" as describe by his brother, the patient has abdominal pain, nausea and vomiting and says the light hurts his eyes, now all he has been saying since arriving in the ED is " get your shine on!"
Physical Exam
You notice a shuffling gait, and hand tremors
and this tattoo on his arm
You suspect the patient is a local boot legger and you remember that methanol is a byproduct during the fermentation process of fruits. You draw labs, toxicology, and collect urine analysis
Labs
WBC: 6
Ethanol level is with in normal limits
PH 7.30
Cr. 1.0
Glucose 100 mg/dl
Anion Gap is 30
Osm Gap is 20
Lactic Acid is 4
UA: Shows ketones
Plasma methanol > 20 mg/dl
salicylate level and acetaminophen are not elevated
Vitals: 110/80mmhg, HR 90, RR 14, Temp 98.0F, SPO2 98%
You note he has a high anion gap metabolic acidosis and notice an high osmolar gap ( mostly seen in toxic alcohol ingestion ) with normal renal function. So you suspect Methanol ingestion and toxicity.
You are concerned for the complications of the the methanol metabolite formic acid; such as
CNS depression ( possibly needing intubation), significant acidemia with a high anion gap metabolic acidosis ( potentially needing hemodialysis )
optic nerve/retina toxicity ( causing blindness )
and neurological symptoms such as parkinsonism syndrome and features.
Your photographic memory that you have had since med school allows you to recall this image instantly
Your plan is to competitively inhibit Alcohol Dehydrogenase
with Fomepizole or Ethanol and save the patient!
So What if ?
What if the PH is less than 7.3?
- Then Start Sodium Bicarbonate drip
- This patient is headed towards hemodialysis!
What if there is a significant acidemia, end organ damage, neurologic symptoms?
- Then emergent hemodialysis is needed
- Hemodialysis removes methanol and formic acid
What If I need to further metabolize the formic acid ?
- Then Add IV Folic Acid or Folinic acid
- Why? Because this is a cofactor to hasten formic acid to its by products of CO2 and H2O
Case Clues - Methanol Toxicity
- Visual Blurring, hand tremors and shuffling gait ( Methanol metabolite formic is toxic to the optic nerve / retina, and Brain/Basal Ganglia )
- He is a suspected moon shiner or boot legger ( note his tattoo ), methanol is distilled first at the start of the run if he sampled this
then as little as 10 - 30 ml can cause blindness and death.
- He has a high anion gap 30 , he has a high osmolar gap 20 , and PH 7.30
- He has elevated lactic acid and elevated ketones which is also seen in methanol toxicity
- His normal glucose rules out DKA
- He has normal WBC Count, stable vitals, and afebrile so sepsis/shock
- Salicylate level and acetaminophen are not elevated
Notable Notes - Methanol Toxicity
- Found in windshield wiper fluid, anti freeze, moon shine fermentation
- Ingestion causes a a high anion gap metabolic acidosis and an osmolar gap
- Metabolism chart
- Formic Acid is toxic to the optic nerve and brain/basal ganglia so can cause blindness and Parkinsonism syndrome
- Treatment:
- Correction of metabolic acidosis when the PH < 7.30 with sodium bicarbonate drip
- Competitively Inhibit Alcohol Dehydrogenase with Fomepizole/Ethanol
- Hemodialysis for high anion gap and severe acidemia, end organ damage or neurological manifestations
- Add IV Folic Acid to hasten formic acid metabolism to CO2 and H2O
What is the Osmolar Gap?
Osm measured - Osm calculated
- Osm Gap Indicates the presence of an abnormal solute, but think Alcohols (Methanol, Ethylene Glycol, Ethanol, Isopropyl Alcohol)
- Should be less than < 10
- but High Osm gap is > 20 mmol/L is seen in Methanol and Ethylene Glycol Toxicity
The Differentials ( Why not? )
Why not Ethylene Glycol Ingestion?
- Case Clues: Ethylene Glycol looks a lot like Methanol toxicity but remember Ethylene glycol is more toxic to the kidneys, so in the case look for AKI, flank pain, hematuria, and calcium oXalate crystals
Why Not Alcohol ingestion with Ketoacidosis?
- Case Clues: There would be a high anion gap, and osmolar gap, the ethanol level and ketones would also be elevated
Why not Isopropyl Alcohol Ingestion?
- Case Clues: There would be a High Osmolar Gap but No Metabolic Acidosis is seen in Isopropyl alcohol toxicity
Why Not Lactic Acidosis?
- Case Clues: The Lactic Acid level would be elevated and there would be a suspicion of sepsis/shock
Why Not Salsylate ingestion?
- Case Clues: This is the classic case of metabolic acidosis and respiratory alkalosis, with a normal Osmolar gap
Why not DKA?
- Case clues: The blood sugar > 250 , and ketones ( Beta hydroxybutyrate. ketonuria ) presenting as a high anion gap metabolic / ketoacidosis
Why not Starvation Ketosis?
- Case Clues: This is seen in the setting of starvation and malnutrition, and will have a high anion gap but normal osmolar gap, with elevated ketones
Know if for the Boards - Methanol Toxicity!
- Methanol Toxicity causes a high anion gap metabolic acidosis with a high osmolar gap ( so does Ethylene Glycol!)
- Methanol metabolite is formic acid and is toxic to the optic nerve and retina that can cause blindness
- So remember Methanol is toxic to the eye ( vision loss) and Brain/ Basal ganglia ( Parkinsonian syndrome ) vs Etyhlene glycol is toxic to the kidney ( AKI, Flank Pain, Hematuria, and Calcium oXalate stones)
- A High Osm Gap > 20 mmol/L ( so suspect the presence of a toxic alcohol)
- Competitively Inhibit Alcohol Dehydrogenase with Fomepizole/Ethanol
Want to know more?
