Acquired vWD in ET — RACP Adult Medicine MCQ

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HardHaematologyAcquired vWD in ETRACP Adult Medicine

A 65-year-old man with essential thrombocythaemia (CALR mutation positive) has a platelet count of 1,200 × 10⁹/L. He is 67 years old with no prior thrombosis. He develops bleeding from his gums. What should be assessed?

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Correct answer: B — D-dimer

In MPN patients with extreme thrombocytosis (>1,000 × 10⁹/L), acquired von Willebrand disease (AvWD) can occur due to adsorption and proteolysis of high-molecular-weight vWF multimers by the excess platelets. This paradoxically causes a BLEEDING phenotype despite thrombocytosis. Testing vWF antigen and ristocetin cofactor activity (which measures vWF function) confirms the diagnosis. Aspirin should be WITHHELD until vWF normalises. Cytoreduction (hydroxyurea) to lower the platelet count restores vWF levels.

Reference: eTG – 2025 – Haematology; EHA – 2022 – MPN Guidelines