**Question:** In polycythemia vera all are true except

A. Erythropoietin levels are increased
B. Decreased red cell distribution width (RDW)
C. Increased white blood cell (WBC) and platelet count
D. Absence of bone marrow fibrosis

**Correct Answer:** .

**Core Concept:** Polycythemia vera (PV) is a myeloproliferative neoplasm characterized by excessive production of red blood cells, platelets, and sometimes white blood cells. PV is caused by the Philadelphia chromosome, a genetic mutation that leads to uncontrolled proliferation of myeloid cells in the bone marrow.

**Why the Correct Answer is Right:** In PV, erythropoietin (EPO) levels are increased as the body overcompensates for the excessive red cell production, aiming to maintain adequate oxygen delivery despite the elevated RBC count. However, the increased EPO levels do not address the root cause of the disease.

**Why Each Wrong Option is Incorrect:**

A. Erythropoietin levels are increased: As explained above, PV patients have increased EPO levels to compensate for the elevated RBC count, not the primary cause of PV (myeloproliferative disorder).

B. Decreased red cell distribution width (RDW): RDW is a measure of red cell size variation and is not directly related to the primary cause of PV or its pathophysiology.

C. Increased white blood cell (WBC) and platelet count: While PV patients may have increased WBC and platelet counts, these options are not specific to PV and are not the primary cause of the disease. PV primarily affects the erythropoietic and megakaryocytic lineages leading to excess RBC and platelet production.

D. Absence of bone marrow fibrosis: Although bone marrow fibrosis is a common feature in polycythemia vera, it is not the primary cause of the disease. PV is primarily characterized by the clonal proliferation of myeloid cells, specifically the overproduction of RBCs, platelets, and sometimes leukocytes.

**Clinical Pearl:** A thorough understanding of the key features of PV is essential for accurate diagnosis and treatment planning. A high index of suspicion, careful clinical examination, and appropriate laboratory investigations, such as complete blood count (CBC) and bone marrow examination, are critical for diagnosing PV.