Q. I was reading over some of your blog posts (which are awesome) and I came across the one where you stated that “Essential thrombocythemia is not considered a cause of disseminated intravascular coagulation.” And later you write that “patients with essential thrombocythemia can either have abnormal clotting or abnormal bleeding.”

I remember from class that patients with DIC can suffer from BOTH excessive bleeding (hemorrhages) and clotting, simultaneously. If essential thrombocythemia is not considered a cause of DIC, but it can cause both clotting and bleeding, why isn’t it related at all to DIC (since DIC also causes both clotting and bleeding)?

Further, I’m kind of unclear how it’s possible for DIC to cause both bleeding and clotting at the same time. What is the mechanism for this weird combination?

A. Great questions. Yes, patients with essential thrombocythemia (ET) are susceptible to either excessive bleeding or clotting or both. However, their bleeding and/or clotting is different than that which occurs in disseminated intravascular coagulation (DIC), both in mechanism and severity.

In DIC, there is some sort of insult to the endothelium (like sepsis), or some sort of coagulation-activating agent (such as amniotic fluid) that gets dumped into the blood. Whatever the initial instigating factor, a flurry of seemingly unstoppable clotting occurs throughout the body. The exact means by which this occurs (for example, why it occurs in some patients and not others) is not entirely clear. Nor is it well understood why the clotting and bleeding seem to happen at the same time in these patients (I prefer to think that the clotting happens first, and that uses up all the platelets and coagulation factors, leading to bleeding…but it seems to happen in more of a simultaneous fashion, which doesn’t make sense).

The clotting and bleeding in ET has different mechanisms. The “clotting” is really just accumulation of platelets in small vessels (because of the tremendous number of platelets floating around in the blood!). It’s not clotting in the true sense of the word, where you get something initiating the coagulation cascade and binding platelets together. It’s really more of a sludgy type of process. The bleeding, too, is due to other mechanisms, most notably the development of a secondary (not genetic) von Willebrand disease, a weird thing that can happen in certain totally unrelated diseases like benign monoclonal gammopathies, hypothyroidism, lupus, and Wilm’s tumor. The pathogenesis of secondary von Willebrand disease, by the way, is yet another incompletely-understood thing. It may have something to do with immunoglobulins that clear or inactivate von Willebrand factor. Whatever.

The clotting and bleeding in ET is also of a different magnitude (ususally). DIC is often a tumultuous, scary process, whereas the clotting/bleeding in ET is more of a chronic, slow process. It can become severe, but it does not usually have the same acute, life-threatening course that DIC often does.

ET on a Pizza Hut glass: EraPhernalia Vintage