Sunday, March 1, 2020

Acquired Von willebrand disease

Von Willebrand disease is one of the most commonly encountered congenital bleeding disorders in clinical practice. Broadly speaking they are classified as type 1, 2A, 2B, 2M, 2N, and 3. Each one of them is distinct from the other in subtle ways.

However, it could be acquired in a number of ways.

 a.) In patients with thrombocytosis > 1 million cells/ microliter, especially in essential thrombocythemia, loss of HMW  vWD multimers leads to reduced vWF Ristocetin activity: vWF antigen ratio (<0.6)  suggesting type 2 like pattern.

 b.) In patients with aortic stenosis, due to extreme shear stress, vWF unfolds prematurely at the site of the valve revealing ADAMTS13 binding sites, ultimately resulting in its cleavage and loss of HMW multimers. So basically, it could be visualized as the pattern that is just opposite to TTP wherein defective ADAMTS13 activity results in excess of HMW vWF multimers.

It is often associated with either angiodysplasia or AVMs of the GI tract that further predisposes to bleeding. Although the exact pathogenesis of these lesions is not understood, one postulated mechanism suggests chronic colonic ischemia leading to sympathetic nervous system-induced vasodilation as a potential culprit.
 In this context, it is also known as Heyde's syndrome.

c.) Sometimes in severe hypothyroidism, often the production of vWF by endothelial cells itself is markedly reduced.

d.) Rarely in the setting of multiple myeloma and various other neoplasms, tumor cells express the excess of Gpllb/llla leading to enhanced clearance of vWF from circulation.

One of the common lab findings in acquired vWD is reduced vWF Ristocetin activity: vWF antigen ratio pointing to the disproportionate decrease in activity compared to antigen levels.
It is due to the loss of HMW  multimers.

- Kirtan Patolia

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