Can't remember the details but:
55 year old Japanese man eating pickled fish and leafy vegetables found to have gastric cancer. He undergoes gastric resection and 6 months later is found to have fatigue, pallor, MCV 120, low hematocrit.
Answer was B12 deficiency. 75% (or something) of people chose this. Any care to comment?
(I'm referring to the fact that the liver stores 2-3 years worth of B12 and yet he developed deficiency in 6 months)
Macrocytic Anemia has
THREE possibilities: B12, Folate, and Liver Disease. You must first look at a smear to differentiate between megaloblastic (impaired DNA synthesis) and nonmegaloblastic (liver disease).
Megaloblastic Anemia has two possibilities: B12 and Folate.
I presume you got
anemia based on the fatigue and pallor. Oh, and the low crit.
I presume you got
macrocytic anemia based on the MCV. This has been pretty easy so far.
Now, your reasoning. You saw
not enough time to be B12. And you are right. Usually, it takes years to decades to develop a B12 deficiency. So, you were probably thinking Folate, right? Its only got a couple of weeks in stores, so if its a macrocytic anemia, and only 6 months have gone by, then it must be Folate.
Ok, not bad reasoning. Lets just pause to recognize that we simply ruled out liver disease because we presumed it was megaloblastic (which it probably was).
But
why would this person who had a gastrectomy have a folate deficiency. What do you need to have folate absorption? Nothing. Well, an intact proximal small intestine. But thats it. Did he have his small intestine resected? Nope. Is there mention of a tea and toast diet? Nope. So, if the question doesn't say anything about diet, you must presume the diet is normal. If the question doesn't say anything about small bowel resection, you presume it is intact. So, it can't be Folate deficiency.
Ok. Let's look at B12. What do you need to have B12 absorption? You need
Intrinsic Factor, which means you need
parietal cells, which means you need a
stomach. Oh, and a terminal ileum. So, this guy has a gastrectomy. He has NO parietal cells, so NO intrinsic Factor, and so can have NO B12 absorption. So its B12.
Ok. You don't like that explanation? Lets look at it from a practical standpoint. This question is asking: if you do a gastrectomy what is one potential complication you have to worry about? Well, it certainly isnt Folate deficieny. But it IS B12 deficiency.
Ok. you don't like that explanation? Lets use the real world. On average, the body has 2-10 years of b12 stored. In
this person he had 6 months supply. Done. Your error was that you put
too much stock in timing and
not enough stock in mechanism
Help?
