Essential Thrombocytosis

This is a patient with Essential Thrombocytosis. This is a myeloproliferative neoplasm which is important to recognise as delayed diagnosis is associated with increased morbidity and poor outcome.

There are a number of features here which are noteworthy. The first is that there are no features of iron deficiency. Iron deficiency is the commonest cause of reactive thromboscytosis, and while the platelet count rarely gets extremely high it is always worth excluding this morphologically (and by testing the ferritin!). The red cells are well haemoglobinised, with no microcytosis, hypochromia or anisochromasia. These should be sufficient to conclude adequate iron status.

The red cells do how some anisopoikiloytosis. This is often thought to be a feature of the bone marrow disorder, but is more likely simply a feature of functional hyposplenism - the splenic macrophages are so busy filtering out platelets that they cannot capture all the red cells which they would normally clear. This is physiological, not pathological.

Neutrophils and other white cells are reactive, showing toxic granulation. 

The platelets which we see are markedly increased and show significant anisocytosis. Remember that platelets are large up to half the size of red cells, giant from half to the full size of the red cell, and are megakaryocyte fragments when they are larger than the red cells. In this case, we see all three. In reactive thrombocytosis, we rarely see mega fragments and giant platelets but they are frequent in primary bone marrow caused of thrombocytosis - ET, AML (particulary M7/megakaryoblastic), and TAM.

Overall, there are no features of iron deficiency with markedly increased and abnormal platelets. This should raise suspicion of ET or another MPN. Correlation with molecular testing, bone marrow biopsy and clinical history is recommended.