Polycythemia vera (erythemia)
Polycythemia vera is a clonal neoplasm originating from myeloid tissue. According to epidemiological data, the condition has an incidence of $1:100,000$. Men over the age of 40 are most susceptible to this disease.
The core pathogenesis lies in the sharply increased production of erythroid cells. However, this process is not limited to red blood cells alone: it is closely combined with the excessive proliferation of granulocytopoietic and megakaryocytopoietic cells.
Laboratory parameters in polycythemia vera have clear criteria:
- A marked increase in total red blood cell mass (the value exceeds $7 \times 10^{12}/\text{L}$).
- A high hemoglobin level, which rises above $180 \text{ g/L}$.
- A concurrent increase in hematocrit.
The outcome of the disease is largely determined by changes in the rheological properties of the blood. Patients die from severe complications directly associated with the development of arterial hypertension or the occurrence of fatal thromboses.
Chronic idiopathic myelofibrosis
In medical literature, this condition has several synonyms: subleukemic myelosis, aleukemic myelosis, as well as osteomyelosclerosis.
The pathogenesis of the disease represents a sequential chain of events:
- Primary tumor proliferation occurs in the bone marrow. It primarily affects the megakaryocyte and granulocyte pools.
- Specific growth factors are actively released from the resulting abnormal megakaryocytes and circulating platelets.
- These factors act as a potent stimulus for the activation of fibroblasts. The result is a massive proliferation of reticulin and collagen fibers, which forms the picture of severe fibrosis.
The peripheral blood picture in myelofibrosis is radically different from polycythemia: pancytopenia is observed, meaning a total decrease in the count of all blood cellular elements. The prognosis for patients remains serious, as in approximately 10% of cases the pathology transforms into acute leukemia.
Essential thrombocythemia
Essential thrombocythemia is characterized as a very rare disease of the hematopoietic system. The morphological basis of the pathology is marked megakaryocytic hyperplasia, which naturally leads to the excessive production of platelets.
Laboratory data for this form are quite specific:
- The platelet count in the peripheral blood reaches extreme values, frequently exceeding $1000 \times 10^9/\text{L}$.
- Neutrophilic leukocytosis is simultaneously recorded in the assays.
The clinical presentation has a paradoxical feature. Multiple hemorrhages become the leading manifestation. This is due to the fact that the vast mass of circulating platelets has pronounced functional defects that prevent them from participating adequately in hemostasis.
The evolution of the disease can follow two paths: most commonly, transformation into myelofibrosis occurs, and in rarer cases, progression to acute myeloid leukemia is observed.
Borderline and rare forms
The classification also distinguishes rare forms of chronic leukemias. These include chronic neutrophilic leukemia and chronic eosinophilic leukemia (the latter also known under the term hypereosinophilic syndrome).
A special place is occupied by myelodysplastic/myeloproliferative neoplasms. This is a broad group concept that unites various borderline states of the hematopoietic system. This group includes the following nosological forms:
- Chronic myelomonocytic leukemia.
- Atypical chronic myeloid leukemia.
- Juvenile myelomonocytic leukemia (synonyms may be found in literature: juvenile chronic myeloid leukemia or juvenile chronic myelomonocytic leukemia).
Briefly: answers to topical questions
What genetic mutations underlie the pathogenesis of polycythemia vera?
The pathogenesis of polycythemia vera is based on mutations in the JAK2 gene. These include:
- JAK2 V617F mutation (in some cases designated as V617ZF).
- Mutations in exon 12 of the JAK2 gene.
These genetic alterations affect a gene whose product is involved in signal transduction from hematopoietic factor receptors. As a result of the mutation, hematopoietic cells become excessively sensitive to the action of these factors, and the proliferation rate of myeloid cells increases pathologically even at normal levels of stimulants (e.g., erythropoietin).
What clinical syndromes are characteristic of the advanced stage of polycythemia vera in addition to thrombosis and arterial hypertension?
In addition to thrombosis and arterial hypertension, polycythemia vera is characterized by a specific vasomotor syndrome, neurological symptoms, plethora, and splenomegaly.
- Vasomotor syndrome — manifests as erythromelalgia (burning pain in the fingertips accompanied by their redness).
- Plethora — marked hypervolemia and engorgement.
- Splenomegaly — enlargement of the spleen, which is palpable in 75% of patients.
- Pruritus (pruritus).
Patients may also develop various neurological symptoms.
What changes in the bone marrow trephine biopsy are characteristic of essential thrombocythemia?
The morphological picture of the bone marrow in essential thrombocythemia is characterized by megakaryocytic hyperplasia and excessive platelet production.
The leading signs of the three main diseases can be memorized by the predominant lineage: Erythemia — excess red blood cells, Thrombocythemia — excess platelets, Myelofibrosis — replacement of bone marrow with connective tissue (fibrosis).
Class and exam questions
Why do hemorrhages occur in essential thrombocythemia if the platelet count is very high?
Despite the colossal number (over 1000 × 10⁹/L), these platelets have severe functional defects. They are incapable of adequately participating in hemostasis, which paradoxically leads to hemorrhagic syndrome.
What is the most frequent cause of death in patients with polycythemia vera?
The main cause of fatal outcomes is severe complications caused by arterial hypertension and massive thromboses against the background of marked blood hyperviscosity.
How does fibrosis develop in chronic idiopathic myelofibrosis?
Abnormal megakaryocytes and platelets actively release growth factors. They stimulate fibroblasts, which begin to massively synthesize reticulin and collagen fibers in the bone marrow.
What else to study on this topic
- Chronic neutrophilic leukemia
- Chronic eosinophilic leukemia and hypereosinophilic syndrome
- Chronic myelomonocytic leukemia
- Atypical chronic myeloid leukemia
- Juvenile myelomonocytic leukemia
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