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Retired NBME 18 Answers

nbme18/Block 2/Question#37 (reveal difficulty score)
A 45-year-old man comes to the physician ...
Pulmonary arteriovenous shunting ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—anechakfspb(77)
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This is describing hereditary hemorrhagic telangiectasia (FA 2019 p. 312). It is also known as Osler-Weber-Rendu syndrome. It is an autosomal dominant disorder of blood vessels. Findings include blanching lesions (telangiectasias) on skin and mucous membranes, recurrent epistaxis, skin discolorations, AV malformations, GI bleeding, and hematuria.

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cbreland  Wow, I was completely lost on this one, thanks! +32
jbrito718  What helped me figure this out was the finger clubbing. This sign indicated hypoxia. Along with what I thought were micro-clots of small vessels (now I know are telangiectasia) would most likely cause increased shunting in the lungs. +1
thegout  UW added questions about this pathophys recently. Megakaryocytes mature into platelets in the pulmonary circulation,so if blood bypasses the lungs in any way( COPD,CF,AV shunting,congenital heart defects) immature megakaryocytes enter blood stream, these megakaryocytes actually cause the clubbing by secreting growth factors like PDGF.And the bleeding spots are just a complication of lack of mature platelets in blood. So any time you see clubbing, you should know the pathophysiology involves megakaryocytes. +6



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