Review Question - QID 109194

This patient presents with headaches, blurry vision, bruising, hepatosplenomegaly, and enlarged retinal veins suggestive of polycythemia vera (PV). In this condition, plasma volume is elevated, RBC mass is elevated, EPO is decreased, and SaO2 is normal.

PV is a myeloproliferative neoplasm that is caused by a JAK2 kinase mutation that leads to increased RBC production. The elevated RBC mass leads to highly viscous blood that can present with headaches, blurry vision, bleeding from engorged vessels, constitutional symptoms, and pruritis due to histamine release by increased basophils. In a patient with PV at steady state, the plasma volume will demonstrate a mild compensatory increase to accommodate for the increased RBC mass. Serum EPO will be low given the elevated RBC mass and SaO2 will be normal. Other key findings include an elevated hemoglobin and elevated hematocrit.

Spivak discusses the effect of polycythemia vera on plasma volume. Specifically, he notes that plasma volume may either remain unchanged or increases as hematocrit rises in this disease.

Incorrect Answers:
Answer 2: Ectopic EPO production, most frequently by renal cell carcinoma, is characterized by a normal plasma volume, elevated RBC mass, elevated EPO, and normal SaO2.

Answer 3: Dehydration is characterized by a decreased plasma volume, normal RBC mass, normal EPO, and normal SaO2.

Answer 4: Hypoxemia is characterized by a normal plasma volume, elevated RBC mass, elevated EPO, and decreased SaO2.

Answer 5: Chronic kidney disease presents with decreased RBC mass due to a decreased ability to produce EPO. It also leads to an increased plasma volume due to activation of the renin-angiotensin-aldosterone system. SaO2 will be normal except in severe cases.

Bullet Summary:
Polycythemia vera is a myeloproliferative disorder characterized by increased plasma volume, increased RBC mass, decreased EPO, and normal SaO2.