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NBME 23 Answers

nbme23/Block 2/Question#5 (35.6 difficulty score)
A female newborn develops respiratory ...
Osteogenesis imperfecta, type IπŸ”
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 +7 
submitted by seagull(1389),
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heT nyndrgeilu nmcihamse is yuulals a olbrmpe ithw otnnvceeic esiuts ued to a calk of tpey I gcaoll.ne hsTi rsoccu ni meor htan %90 of sacse ued ot ottmuisna in the 11OCLA or COA21L sge.ne sheTe inteecg mbesprlo era eontf etnhriedi mfro a n'oresps ptanser in na maasoltuo tanniomd arnmen or occru vai a wne mntit.aou

kiiW-

acslliB,ay ogdo *gi**nf lku!c

focus  Picture of "wormian bones", just for fun: http://www.learningradiology.com/archives2010/COW%20432-Wormian/wormiancorrect.htm +1  



 +6 
submitted by hungrybox(961),

TLDR: Physical symptoms >> family history or anything else.

Like the other guy said, I got played hard.

I thought:

β€’ poor prenatal care

β€’ no family history

β€’ bone problem/fractures

Instantly pointed to Rickets.

BUT, in retrospect this is key:

β€’ intercostal retractions (vs. rachitic rosary β†’ costchondral thickenings)

They're basically telling you to rule out Rickets. It seems 100% unfair b/c poor prenatal care seemed to rule in Rickets. The no family history seems to rule out OI.

But I guess what I've learned is, physical symptoms trump ANYTHING ELSE on NBMEs.




 +5 
submitted by pizzapack(5),

So once you're down to OI and Rickets think about the pathogenesis of the two diseases and ignore the rest of the stem for a second. Bone is basically two parts. A fibrous "rebar" part and a calcium "cement" part. OI has defective type 1 collagen leading to bones that have no problem mineralizing (cement) but are lacking the rebar. This leads to super brittle bones that break all the time. Like hundreds of fractures.

Vit D deficiency causes an inability to mineralize but has no problem with laying down the collagen or "rebar". As a result you get soft and bendy bones. Sure they can break but the main problem is lack of strength.

From there you pick OI because the kid has 1000 fractures. Rickets wouldn't present that way.

Also bonus buzzword: apparently "wormian appearance" is an important diagnostic clue for OI.




 +2 
submitted by nukie404(7),
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At ristf I aws kiintnhg a!ha hldCi beus!a utB I esugs miwnroa onsbe are mreo gvsseguite of ,IO ugtohalh teh no falmyi hx patr aws arehrt bel.h

thotcandy  Literally had it on OI until I saw no family hx... Isn't it AUTOSOMAL DOMINANT? +2  
faus305  FA 2019 pg. 51. Yes it is autosomal dominant. This question is poorly written but the clues are "wormian bones" and multiple fractures. Pretty sure everyone on this page would've nailed the diagnosis if seeing a real patient instead of using three lines of text with two hints. Questions like this demonstrate how this test became a way of ranking people based off of minutia they know and not their clinical abilities. This is why step is pass/fail in 2 years. +  



 +1 
submitted by lispectedwumbologist(102),
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How si sith het aernws if theer si on yfliam yihstor fo rrtuercne ?crtersfau I hhtotgu osseistegnoe fcmtpireae saw ooaamlsut mnido?tan

seagull  Exactly!! it's an autosomal dominate disease! +10  
emcee  Autosomal dominant diseases are variably expressive. Still, I think this was a badly written question (should have given us some family history). +  
wutuwantbruv  Also, FA says that fractures may occur during the birthing process, which is what I believe they were going for. I don't believe these findings would be seen at birth with any of the other choices. +  
d_holles  Yeah I thought I outsmarted NBME by selecting Rickets bc it said no family history ... guess I got played lol. +9  
jean_young2019  Could it be a sporadic cases? Spontaneous Mutation This is a change in a gene that occurs without an obvious cause, in a family where there is no history of the particular gene mutation. OI is inherited as an autosomal dominant trait. Approximately 35% of cases have no family history and are called "sporadic" cases. In sporadic cases, OI is believed to result from a spontaneous new mutation. http://www.oif.org/site/PageServer?pagename=Glossary +6  
avocadotoast  Amboss says the severe subtypes (types II, III) of OI are usually due to a new (sporadic) mutation in COL1A1 or COL1A2, while patients with the mild forms (types I, IV) typically have a parent with the condition. +  



 +1 
submitted by azibird(158),

Would rickets present in a newborn? This article describing a case series says "There are few other published cases of congenital rickets caused by maternal VDD." So maybe rickets usually presents later in life. Mayo Clinic says it's usually after "an extreme and prolonged vitamin D deficiency."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2795674/ https://www.mayoclinic.org/diseases-conditions/rickets/symptoms-causes/syc-20351943

rongloz  This was exactly my reasoning of choosing Osteogenesis versus Rickets +