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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
Lipoic acid
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


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:
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

Anonymous said...

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