What is Polycythemia?
Polycythemia is a condition characterized by an abnormally elevated red blood cell mass, which can be either primary (polycythemia vera, a clonal myeloproliferative neoplasm) or secondary (due to other causes like hypoxia or tumors). 1
Polycythemia Vera (PV) - The Primary Form
Polycythemia vera is a Philadelphia chromosome-negative myeloproliferative neoplasm caused by mutations in the JAK2 gene (present in >97% of cases), resulting in uncontrolled proliferation of red blood cells, and often white blood cells and platelets as well 2.
Key Diagnostic Features
According to WHO 2016 criteria, PV diagnosis requires 3:
Major Criteria:
- Hemoglobin >16.5 g/dL (men) or >16 g/dL (women), OR hematocrit >49% (men) or >48% (women), OR increased red cell mass
- Bone marrow showing hypercellularity with trilineage myeloproliferation
- Presence of JAK2 mutation (V617F or exon 12)
Minor Criterion:
- Subnormal serum erythropoietin level
Diagnosis requires all 3 major criteria OR the first 2 major criteria plus the minor criterion 3.
Clinical Presentation Matching Your Patient
Yes, polycythemia vera could absolutely account for this patient's constellation of symptoms. The clinical picture you describe is highly consistent with PV:
Hematologic Features:
- Increased red blood cell mass - the hallmark finding 1
- High mean platelet volume - thrombocytosis occurs in PV as part of the trilineage myeloproliferation 3
Constitutional Symptoms (Common in PV):
- Fatigue - one of the most frequently reported symptoms, present even with controlled blood counts 4
- Sensation of heat and scalp burning - characteristic of PV, related to hyperviscosity and inflammatory cytokines 5
- Muscle and joint pain - part of the constitutional symptom burden 5
Vascular Symptoms:
- Cold extremities - can result from hyperviscosity and microvascular disturbances 6
- Dyspnea - related to increased blood viscosity and potential thrombotic complications 5
The elevated right hemidiaphragm warrants specific attention - this could represent splenomegaly (which occurs in PV) displacing the diaphragm, or potentially a thrombotic complication affecting the hepatic or splenic vasculature, as PV carries the highest incidence of thromboembolic complications among myeloproliferative neoplasms 1.
Critical Pathophysiology
PV results in hyperviscosity due to increased red cell mass, which paradoxically increases plasma volume as well 1. This creates a unique situation where the hematocrit may not accurately reflect the true red cell burden. Unless hematocrit exceeds 59%, true erythrocytosis cannot be distinguished from pseudoerythrocytosis due to plasma volume contraction 1.
Important Clinical Pitfall
Symptom burden in PV persists despite control of blood counts 4. This means that achieving normal hematocrit through phlebotomy does not necessarily resolve constitutional symptoms like fatigue, pruritus, or the sensation of heat. The discordance between laboratory values and symptom burden suggests that inflammatory cytokines and other factors beyond red cell mass contribute to the clinical picture 4.
Prognosis and Complications
PV is characterized by 5:
- Shortened overall survival due to thrombotic events (stroke, MI, PE, DVT)
- Risk of transformation to acute myeloid leukemia or myelofibrosis
- Life span typically measured in decades even with myelofibrosis present 1
Next Steps for This Patient
Immediate workup should include:
- JAK2 V617F mutation testing (positive in >97% of PV cases) 2
- Serum erythropoietin level (typically subnormal in PV) 3
- Bone marrow biopsy if diagnosis remains uncertain 3
- Imaging to evaluate the elevated hemidiaphragm and assess for splenomegaly or thrombotic complications
- Complete blood count with differential to assess all three cell lines
The combination of increased red cell mass, high platelet volume, and this specific symptom complex (particularly the sensation of heat and scalp burning) makes polycythemia vera the leading diagnosis to investigate.