American Board of Internal Medicine (ABIM) Certification Practice Exam

Which of the following is a key feature seen on the bone marrow examination of essential thrombocythemia?

1. General hypercellularity

2. Presence of eosinophils

3. Hyperplasia of lymphocytes

4. Presence of granulomas

The correct answer is: General hypercellularity

In essential thrombocythemia (ET), one of the hallmark findings on bone marrow examination is general hypercellularity. This reflects the increased proliferation of megakaryocytes, the bone marrow cells responsible for the production of platelets. In ET, there is a marked increase in the number of megakaryocytes, which can lead to elevated platelet counts in the peripheral blood. This hypercellularity is specific to ET and is a crucial aspect for diagnosis, as it indicates that the marrow is active and producing more cells than usual. The presence of eosinophils, hyperplasia of lymphocytes, or granulomas would not be characteristic of essential thrombocythemia. Eosinophils typically indicate a response to allergies or parasitic infections, lymphocyte hyperplasia would suggest a different pathology such as a reactive process or malignancy, and granulomas are generally associated with inflammatory conditions or infections. These findings would not align with the expected alterations seen in the bone marrow of a patient with essential thrombocythemia, further highlighting the importance of hypercellularity in this specific context.