All of the following are seen in polycythemia rubra vera except –
**Core Concept**
Polycythemia rubra vera (PRV) is a myeloproliferative disorder characterized by the excessive production of red blood cells, white blood cells, and platelets. This condition is caused by a mutation in the JAK2 gene, leading to the activation of the JAK-STAT signaling pathway, which promotes cellular proliferation.
**Why the Correct Answer is Right**
In PRV, there is an increase in the production of all three blood cell lines. However, one of the distinguishing features of PRV is the presence of a characteristic histopathological finding in the bone marrow: the presence of a "leukemic reticulin" fibrosis. This is due to the increased production of collagen by fibroblasts, leading to a dense reticulin network in the bone marrow. This feature is typically seen in PRV and is not a characteristic of other myeloproliferative disorders.
**Why Each Wrong Option is Incorrect**
**Option A:** Leukemic reticulin fibrosis is indeed a hallmark of PRV, so this option is incorrect.
**Option B:** While anemia is a common finding in PRV, it is not typically seen in the early stages of the disease, and the presence of anemia does not rule out a diagnosis of PRV. However, the question is asking for an exception to the typical features of PRV, and anemia is not the best answer.
**Option C:** Thrombocytopenia (low platelet count) is not typically seen in PRV, as the disease is characterized by an increase in platelet production. This option is the best answer.
**Clinical Pearl / High-Yield Fact**
In PRV, the increased red blood cell mass can lead to increased blood viscosity, which can cause symptoms such as headache, dizziness, and visual disturbances. This is known as "erythromelalgia," and it is a classic symptom of PRV.
**Correct Answer:** C. Thrombocytopenia.