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Tuesday, April 17, 2007

Thiamine is HY for the USMLE Step 1

THIAMINE aka Vitamin B1
Active form: Thiamine Pyrophosphate (TPP)

Main reactions in which thiamine is a cofactor:
These dehydrogenase reactions generate NADH in the mitochondria which enter the electron transport chain to generate ATP, therefore the patient has a problem making ATP.

Cofactors required by the above 2 enzymes are
Thiamine
Lipoic acid
CO2
Folate
NAD+
Which can be remembered by the phrase, "Tender Love and Care for Nancy"


(Thiamine is also a cofactor for transketolase which catalyzes 2 Carbon transfers in the HMP shunt (pentose phosphate pathway) - required to make Ribose 5 phosphate for nucleotide synthesis)



Classic patient is a Malnourished Alcoholic
Signs and symptoms of deficiency:

Wernicke's Encephalopathy


  • Peripheral neuropathy
    • due to Wallerian degeneration; not drawn (source: Boards and Wards, 3rd Edition)
    • occurs since ATP is needed for myelin production and ATP isn't being made to the same quantity
    • Neuropathy may manifest as foot drop or wrist drop much like lead poisoning does in adults
  • Wernicke's encephalopathy is reversible (We-versible Wernicke's)
________

Say the above patient was given glucose without correcting his thiamine deficiency, it would precipitate...

Korsakoff's Amneisa

These are the Mammillary Bodies:

These are the mammillary bodies on drugs:

Any questions?
(source: The Medical Journal of Australia )

  • anterograde and retrograde amnesia
  • Bilateral hemorrhagic necrosis of mammillary bodies
  • mammillary bodies are in the hypothalamus and are part of the limbic system
  • irreversible
Treatment: IV Thiamine and THEN glucose

5 comments:

VS said...

hey dude, one of your PDH cofactors is wrong. Its not CO2, its CoA (Co-enzyme A). CoA derives from pantothenic acid, which is B5

so the PDH complex, along with a-kg DH and I believe a-ketoacid DH (aka Branched chain amino acid dehydrogenase) use:
B1-thiamine
b2- riboflavin
b3- niacin
b4 - lipoic acid
B5- pantothenic acid

I find remembering B1-5 is pretty simple when we have soo many pneumonics to remember.
nice site.. i like-
ps.. SGU is amazing, but gotta love my AUC

Anonymous said...

I love your wernickes guy
excellent!

Anonymous said...

Why is it that the mamillary bodies specifically become hypotrophic in Korsakoff's Amnesia?

new in the states said...

Very nice explanation

new in the states said...

Very nice explanation