NBME Free 120 von Willebrand disease (NBME Answers)

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free120/Block 1/Question#32 (reveal difficulty score)
A 20-year-old woman comes to the physician ...
von Willebrand disease 🔍 / 📺 / 🌳 / 📖
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submitted by ∗imnotarobotbut(184)

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This is a bad question. Platelet aggregation time being normal, ok fine I can see that. But VWF stabilizes factor 8 and you'd see an increase in PTT (first line next to VWF in First Aid). Why is their PTT normal?

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a1_antitrypsin Totally agree, and they give you a slight increase in PT instead +1

mambaforstep yeah but if they gave you an increase in PTT then Hemophilia A could have been a valid answer choice. so they prob showed a nl PTT to differentiate vWF dz from hemophlia A +1

drpee VWD only sometimes presents with a slightly increased PTT. Don't let those anki facts steer you wrong... Plus all the other answers make no sense. Afibrinogenemia? That means literally no fibrinogin (PT and PTT would be infinitely increased). Hemophelia? Or vitamin K deficiency? Those are coagulation factor disorders so they would present with deep bleeding and large bruising. (Unlike platelet disorders, including VWD, which present with mucosal bleeding, petechiae, and heavy menses). VWD is actually the ONLY one that makes sense. +11

cbreland I get why it's not afibrinogenemia (which is what I picked), but still don't understand how VWD is right. You have normal PTT and normal platelet aggregation (both of which should be abnormal). Is the only thing leading us to VWD is it being a primary bleeding issue? Again, my answer made no sense, but VWD in this context, seems way out there +4

osteopathnproud I agree with you @cbreland once I noticed I had to bend lab values for any answer choice then in my head most of them were possible. I took a step back and answer with the most common bleeding disorder, vW disease. Funny thing is when I retook it to check my answers, I had time to overthink and got it wrong. +2

aakb the anki facts never steer you wrong! my zanki cards say "Low vWF in von Willebrand disease impairs platelet {{c1::adhesion}}" (Gp1B binds to vWF) not platelet aggregation (GpIIbIIIa binds to fibrinogen). additionally it says you can have either a normal or increase PTT. in this case the PT is not increased. It is decreased a little, which I assume is fine esp w an INR of 1.0 +2

lebabs Shut up +7

justanotherimg i agree with @drpee , and we also need to keep in mind that hemophilia(x-linked recessive) wont be likely in this patient a 20 yr old woman +1

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submitted by ∗bwdc(697)

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von Willebrand disease is by far the most common inherited bleeding diathesis. Frequently, the only laboratory abnormality is increased bleeding time (literally you prick the patient and see how long it takes them to stop bleeding). On Step, bleeding women have VWD. Bleeding boys have hemophilia.

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winelover777 Agree. PTT does not have to be elevated to be VWD. +6

tulsigabbard Welp. +1

tekkenman101 Except there's no laboratory verified bleeding time given, only aggregation which has to do with platelet-platelet interaction. +1

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submitted by canyon_run(4)

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why is the platelet aggregation test is normal in VWD? my problem is that Gp1b and VWfactor have to interact to induce a confirmational change in platelets to release ADP –> ADP binds to adp-receptor and induces Gp2b/3a which enables aggregation via fibrinogen. which would lead to abnormal aggregation? and is the ristocetin assay not a platelet aggregation test? or can it sometimes be normal and sometimes not?

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bwdc It can be abnormal as well, depends on the subtype and severity (the wikipedia page does a decent job explaining). The most common subtype of VWD is a quantitative defect, which is often mild/nearly clinically occult and can have essentially normal laboratory testing. This is one of those questions where the labs are really there to exclude the other choices. +7

chaosawaits The platelet aggregation test and the normal PTT steered me away as well, but when you think about it, VWD is a term that includes a variety of deficiencies that can be either quantitative or qualitative. All the other options listed CAN'T be true based on the lab values given. So this question seems to be testing your ability to know which diseases are variable with lab values and which can be easily ruled out based on lab values. +

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submitted by ∗jamespham93(1)

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Pt shows classical signs of lack of platelet ADHESION. ADHESION is mediated by vWF. Platelet AGGREGATION studies test for AGGREGATION, which is mediated by fibrinogen, thus they have normal results on lab testing as they are not testing a pathway that uses vWF (very miniscule detail I know, very annoying).

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