You’re doing a q-bank block and the stem screams “bleeding disorder”… but the answer choices are designed to punish pattern-matching. Von Willebrand disease (vWD) is the perfect example: it mixes primary hemostasis (platelets) with a subtle secondary hemostasis (coagulation) twist. This post walks through a classic vignette, explains the correct answer, then dissects every distractor the way Step questions expect you to.
Tag: Heme/Onc > Hemostasis & Coagulation
The Clinical Vignette (USMLE-Style)
A 22-year-old woman has lifelong easy bruising, recurrent epistaxis, and heavy menstrual bleeding. She reports prolonged bleeding after dental work. Family history reveals similar symptoms in her mother. She is not taking medications. Exam is unremarkable except for scattered ecchymoses.
Labs:
- Platelet count: normal
- PT: normal
- aPTT: mildly increased
- Bleeding time (or PFA): increased
Question: Which of the following is the most likely underlying abnormality?
The Correct Answer: Von Willebrand Disease (Decreased vWF)
What’s actually going on?
Von Willebrand factor (vWF) has two big jobs:
- Platelet adhesion to exposed subendothelial collagen via GpIb
- Carrier protein for factor VIII, protecting it from degradation
So vWD gives you a hybrid picture:
- Primary hemostasis problem → mucocutaneous bleeding (epistaxis, menorrhagia, easy bruising)
- Secondary hemostasis effect (via low factor VIII) → sometimes ↑ aPTT
Expected test pattern
| Finding | vWD |
|---|---|
| Platelet count | Normal |
| PT | Normal |
| aPTT | Normal or ↑ (often mild) |
| Bleeding time / PFA | ↑ |
| vWF antigen / activity | ↓ |
| Factor VIII | Normal or ↓ |
| Ristocetin test | Abnormal (reduced platelet agglutination), corrects with normal plasma |
Treatment (high yield)
- Desmopressin (DDAVP) for many cases (esp. Type 1)
- Increases endothelial release of vWF and factor VIII
- vWF-containing factor concentrates (e.g., for severe disease, major surgery, or if DDAVP ineffective/contraindicated)
Step nuance: vWD is commonly autosomal dominant (esp. Type 1), so a family history across generations fits.
Why Each Distractor Is Tempting (and Why It’s Wrong)
Below are common answer choices Step uses to bait you—and the single detail that should make you reject them.
Distractor 1: Hemophilia A (Factor VIII deficiency)
Why it tempts you: mild ↑ aPTT and “bleeding after procedures.”
Why it’s wrong here: hemophilia causes deep tissue bleeding, not primarily mucocutaneous.
Key differentiators
- Hemophilia A: hemarthroses, muscle hematomas, delayed re-bleeding after surgery
- vWD: epistaxis, gingival bleeding, menorrhagia, easy bruising
Labs
- Hemophilia A: ↑ aPTT, normal bleeding time (platelet function normal)
- vWD: ↑ bleeding time/PFA (platelet adhesion defect), +/- ↑ aPTT
Distractor 2: Hemophilia B (Factor IX deficiency)
Same logic as hemophilia A, but with factor IX.
High-yield tip:
- Hemophilia A = factor VIII
- Hemophilia B = factor IX (“B” for Christmas disease)
Not consistent with: mucosal bleeding + abnormal platelet function testing.
Distractor 3: Bernard-Soulier syndrome (GpIb defect)
Why it tempts you: it’s also a platelet adhesion problem (like vWD), and ristocetin testing comes up.
Why it’s wrong here: Bernard-Soulier typically has thrombocytopenia and giant platelets (macrothrombocytes), and it’s usually autosomal recessive.
Key differences
- vWD: defective vWF → platelet count usually normal
- Bernard-Soulier: defective GpIb → platelet count often ↓, giant platelets
Ristocetin nuance (very testable):
- Both show decreased agglutination with ristocetin
- vWD corrects with normal plasma (because you add vWF)
- Bernard-Soulier does NOT correct (receptor problem, not ligand)
Distractor 4: Glanzmann thrombasthenia (GpIIb/IIIa defect)
Why it tempts you: mucocutaneous bleeding with normal platelet count.
Why it’s wrong here: Glanzmann is a platelet aggregation defect, not adhesion; ristocetin is normal.
Classic
- Defect: GpIIb/IIIa → can’t bind fibrinogen → impaired aggregation
- Labs: ↑ bleeding time/PFA, normal PT/aPTT, normal platelet count
- Tests: Abnormal aggregation with ADP/epinephrine/collagen, normal ristocetin
Distractor 5: Vitamin K deficiency (↓ II, VII, IX, X; also C and S)
Why it tempts you: bleeding + coagulation factor deficiency.
Why it’s wrong here: vitamin K deficiency primarily prolongs PT (factor VII has shortest half-life).
Clues you’d expect instead
- Risk factors: newborn, malabsorption, chronic antibiotics, poor diet
- Labs: ↑ PT (first), later ↑ aPTT too
- Platelet function tests: normal
Distractor 6: Disseminated intravascular coagulation (DIC)
Why it tempts you: bleeding and abnormal coag labs.
Why it’s wrong here: the vignette is chronic and familial. DIC is acute, consumptive, and sick-looking.
DIC profile
- Platelets: ↓
- PT: ↑
- aPTT: ↑
- Fibrinogen: ↓
- D-dimer: ↑
- Schistocytes: may be present
Distractor 7: Immune thrombocytopenia (ITP)
Why it tempts you: mucocutaneous bleeding.
Why it’s wrong here: ITP features isolated thrombocytopenia.
ITP profile
- Platelets: low
- PT/aPTT: normal
- Often: petechiae/purpura, post-viral, autoimmune association
Distractor 8: Aspirin use (COX inhibition → ↓ TXA₂)
Why it tempts you: mucocutaneous bleeding + platelet dysfunction.
Why it’s wrong here: the stem says no meds, and aspirin doesn’t explain mildly ↑ aPTT or a family history.
Aspirin effect
- Platelet count: normal
- PT/aPTT: normal
- Bleeding time/PFA: ↑
- Mechanism: irreversible COX-1 inhibition → ↓ TXA₂ → impaired aggregation
High-Yield vWD Facts You Should Be Able to Blurt Out on Test Day
The “two-hit” concept
- Primary hemostasis defect: impaired platelet adhesion
- Secondary hemostasis effect: decreased factor VIII stability → sometimes ↑ aPTT
Bleeding pattern
- Mucocutaneous: epistaxis, gingival bleeding, menorrhagia, bruising
- Not classic for hemarthroses (that’s hemophilia)
The favorite lab triad
- Normal platelets
- ↑ bleeding time/PFA
- Normal PT, aPTT may be ↑
Ristocetin = vWF-GpIb interaction
- vWD: abnormal, corrects with mixing/normal plasma
- Bernard-Soulier: abnormal, does not correct
Treatment memory hook
- DDAVP for many cases (release stored vWF)
- vWF concentrate if severe/Type 3/major surgery
Rapid-Fire Table: vWD vs the Look-Alikes
| Disorder | Main problem | Bleeding pattern | Platelets | PT | aPTT | Key test clue |
|---|---|---|---|---|---|---|
| vWD | ↓ vWF (adhesion + ↓ VIII) | Mucocutaneous | N | N | N/↑ | Ristocetin abnormal corrects |
| Hemophilia A/B | ↓ VIII / ↓ IX | Deep bleeding, hemarthroses | N | N | ↑ | Normal bleeding time |
| Bernard-Soulier | ↓ GpIb (adhesion) | Mucocutaneous | ↓ | N | N | Ristocetin abnormal no correction |
| Glanzmann | ↓ GpIIb/IIIa (aggregation) | Mucocutaneous | N | N | N | Ristocetin normal |
| Vit K deficiency | ↓ II, VII, IX, X | Variable | N | ↑ | N/↑ | Risk factors (malabsorption/abx) |
| DIC | Consumption | Diffuse bleeding + thrombosis | ↓ | ↑ | ↑ | ↓ fibrinogen, ↑ D-dimer |
How to Beat the Question Next Time
When you see mucocutaneous bleeding, your reflex should be: platelet problem. Then ask:
- Is platelet count normal?
- Yes → think vWD, aspirin, Glanzmann
- No → think ITP, TTP/HUS, Bernard-Soulier, DIC
- Is aPTT elevated too?
- Yes (mild) + mucosal → vWD
- Yes (marked) + deep bleeding → hemophilia
- If they give ristocetin, use it
- Corrects with normal plasma → vWD
- Doesn’t correct → Bernard-Soulier