A patient presents with a decreased level of consciousness and visual disturbances

A patient presents with a decreased level of consciousness and visual disturbances.

Initial investigations reveal an anion gap of 22 and osmolar gap of 24.

What is the most likely cause?

A) ethanol

B) salicylates

C) renal tubular acidosis type 1

D) methanol

E) diabetic ketoacidosis

please explain why and thank you

Good question. Commonly tested.

Some pointers:

The question is likely not going to be that straightforward.

What you’re looking for here is not only an anion gap but also an Osmolar gap.

The toxic alcohols are worth remembering.

Methanol (wood alcohol) commonly found in solvents and antifreeze -> blindness is the buzzword

Ethylene glycol also commonly found in antifreeze. Also causes an osmolar gap. The buzzword here is renal failure. A clue is oxalate crystals in the urine.

Isopropyl alcohol -> rubbing alcohol; cleaning agents. Least toxic of the three. May not always cause an anion gap. What’s special about this one: treatment largely supportive, does not need hemodialysis. Watch out for gastritis and consider a PPI infusion. Unique point - the isopropyl does not have a toxic metabolite. Therefore not dialyzed our or competitively inhibited .

What is the special test for ethylene glycol? A common fluorescent to the alcohol is added in the US and some parts of the world so if you take a wood lamp to the foley bag it can light up (negative woods lamp doesn’t mean it isn’t there it’s just helpful if it lights up)

Common treatment for ethylene glycol and methanol : fomepizole and dialysis

Do you treat isopropyl overdose with fomepizole: No. and remember why - it does not have a toxic metabolite so no point it won’t help. When do you use it ? Often empirically because the patient is altered and very often in toxidromes with altered mentation a good ingestion history is key and often the one thing that isn’t available unfortunately

Treatment if you’re in a rural area with no access to fomepizole or dialysis? IV Ethanol (competitive inhibition for the same enzyme, reducing toxic levels of byproducts and reducing toxicity. Don’t forget this one 👍

When do you treat for these ingestions: if you suspect them as delay leads to significant damage. If you have altered mentation, anion and osmolar gap, it takes times for these tests to come back. Start the fomepizole, call nephrology, and plan for dialysis.

How does fomepizole work: competes with ethylene and methanol for ADH -> fomepizole has an affinity for the receptor that is thousands of time higher than the toxic alcohols and will therefore prohibit toxic metabolites from forming, then you can dialyze our the toxic alcohols if needed.

Sorry for the long post but this is an important topic with significant patient implications. Good question! Good luck with your studies