Case 3: Essential Thrombocythemia (ET)


Stephen Oh, MD, PhD, reviews the case of a 46-year-old female with essential thrombocythemia.

Stephen Oh, MD, PhD: Here we have a 46-year-old woman who is diagnosed with ET [essential thrombocythemia] based on incidental findings during a routine examination. The CBC [complete blood count] shows a platelet count of 525,000 per mm3, a hemoglobin of 12.7 g/dL, and white blood cell count of 9.9 per mm3. A bone marrow biopsy is performed that shows proliferation of megakaryocytes with elevated numbers of enlarged and mature-appearing megakaryocytes. There is no increase in reticulin fibrosis. Molecular testing shows a type 1 CALR mutation.

With this case, and any case where there is consideration for a diagnosis of ET, a question that anyone should be asking is: Is ET the most appropriate diagnosis, or is there a possibility of prefibrotic primary myelofibrosis [pre-PMF], or perhaps some other diagnosis or MPN [myeloproliferative neoplasm]? One of the challenges in distinguishing ET from pre-PMF or early myelofibrosis is that those distinctions can be quite subtle. There are a couple of key points in the WHO [World Health Organization] criteria for these entities. One is that in the case of pre-PMF, there should specifically be megakaryocyte proliferation, atypia, and reticulin fibrosis no greater than grade 1. You can go further and in some cases ask whether we need to make a distinction between pre-PMF and overt primary myelofibrosis? There you would expect to see grade 2 or 3 reticulin fibrosis, as well as many of the other characteristic findings typically present in patients with myelofibrosis. But in a case of ET, you wouldn’t expect to see any significant fibrosis. In both ET and pre-primary myelofibrosis, you could see any of the 3 typical driver mutations: JAK2, CALR, or MPL. The first step in a case like this is to differentiate and be sure of the diagnosis of ET because the prognosis is certainly different over the long term, and the treatment options that would be considered could be different as well.

This transcript has been edited for clarity.

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