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NBME 23 Answers

nbme23/Block 4/Question#28

An 18-month-old girl is brought to the physician ...

Decreased sodium bicarbonate reabsorption in the proximal tubule

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 +14  upvote downvote
submitted by seagull(577),

This is a type II Renal Tubular Acidosis. My Medical School Never taught this to me. Did you also go to poverty med school? I'm surprised they even gave us toilet paper.

mousie  haha mine didn't either. But they usually leave out most high yield info so, to be expected I guess. +1  
yotsubato  I didnt have physiology in my medical school. None, zip, zero, none. Nor did I have biochem. They said "you learned all this shit in undergrad, youll memorize it again for step 1 and forget it promptly" and then just moved on. +2  

 +10  upvote downvote
submitted by smc213(61),

To be completely clear!

This patient has Cystinosis a rare autosomal recessive lysosomal storage disorder and most common cause of Fanconi syndrome in children. Cystinosis is systemic and leads to cystine crystal deposits in cells and tissues throughout the body.

Although Wilsons disease can lead to FS, the crystals in the corneas does not correlate with Wilsons disease.
More info: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4841061/

highyieldboardswards  Thank you! You are a legend for figuring this out! +  
paulkarr  Appreciate you. +  

 +4  upvote downvote
submitted by lamhtu(50),

To be even clearer, this sounds like Fanconi syndrome, which has lead to Type II RTA

 +1  upvote downvote
submitted by nor16(23),

just know where the big stuff / important stuff is resorbed, it is the PCT. No need to know RTAs here...

Keys were the:



-Amino aciduria

Those should be re-absorbed by the PCT, so if they're not, Type 2 RTA.

lamhtu  To be even clearer, this sounds like **Fanconi syndrome, which has lead to Type II RTA** +4  
yb_26  To be even clearer: Wilson disease => Fanconi syndrome => type II (proximal) RTA +  
charcot_bouchard  To be even clearer, you all have been pretty clear +  
charcot_bouchard  To be even clearer, you all have been pretty clear +  

A case of Fanconi syndrome. If it was isolated Type 2 RTA option B would be the answer.

why not decrease CA activity in the proximal tubule? this also could lead to metabolic acidosis.

ergogenic22  carbonic anhydrase inhibitors can cause Type 2 RTA but it is not the cause here (cystinosis) +  

 +0  upvote downvote
submitted by yb_26(89),

Wilson disease => Fanconi syndrome => metabolic acidosis (type II (proximal) RTA)