Here is another case in our growing collection of unknown cases (you can find other cases here, here, here, here and here). These cases are like the ones you see when you’re a medical student or pathology resident rotating through surgical pathology. There’s always an “unknown” conference, and everyone dreads it (or at least I did). Before this conference, you’re supposed to take a look at a bunch of slides under the microscope and formulate a diagnosis for each slide (or, if you’re a medical student, at least a good description and a stab at a general type of disorder). It’s always best to be called on last (or at least not first) – then you can always say, “I have nothing to add,” implying that the previous people explained it so well that there’s nothing left to say.

Here’s a chance to test your knowledge without being judged by anyone. Take a look at the photo, and then the question below, to see if you can make a diagnosis before scrolling down to see the answer.

What is the diagnosis in this blood smear from a 38-year-old female with frequent headaches, and a history of multiple deep venous thrombi and two spontaneous abortions?

A. Thrombotic thrombocytopenic purpura
B. Essential thrombocythemia
C. Acute myeloid leukemia
D. von Willebrand disease
E. Hairy cell leukemia

The diagnosis in this case is essential thrombocythemia. Essential thrombocythemia is a chronic myeloproliferative disorder that is most common in the elderly but has a second, smaller peak of incidence in young women. Patients have a markedly increased platelet count, as seen on this blood smear, often with large and/or hypogranular platelets, as seen at 3 o’clock and 9 o’clock. Patients may present with both thrombotic and hemorrhagic symptoms. The 10 year survival rate is between 60 and 80%.

A is incorrect because although the history is sort of in line with thrombotic thrombocytopenic purpura (thromboses and CNS symptoms), there are TONS of platelets here. In TTP, there are very few platelets (they’re being used up in all the thromboses that are being formed).

C is incorrect because in acute myeloid leukemia, you should see a lot of blasts – and there aren’t any in this photo.

D is incorrect because in von Willebrand disease, you don’t see an increase in platelets in the blood. The problem in von Willebrand disease is that the patient lacks (or has abnormally-functioning) von Willebrand factor, which is the thing that glues platelets onto the subendothelium during clot formation. Patients with von Willebrand disease have a bleeding tendency (because the platelets aren’t sticking), not a clotting tendency.

E is incorrect, although you might have interpreted those very big, very weird-looking platelets at 3 and 9 o’clock as hairy cells. In hairy cell leukemia, patients have a proliferation of malignant “hairy” lymphocytes in the bone marrow. The hairy cells usually don’t get out into the blood in large numbers because the marrow has a lot of fibrosis in this disease (making it hard for the little buggers to get out of the marrow and into the blood).