Myelofibrosis pathophysiology

Pathophysiology
The bone marrow is replaced by collagen fibrosis, impairing the patient's ability to generate new blood cells resulting in a progressive pancytopenia. It is usually reactive following other myeloproliferative disorders, such as polycythemia rubra vera or essential thrombocytosis. Extramedullary hematopoeisis occurs as the haemopoetic cells migrate away from the bone marrow, to the liver and spleen. Patients often have hepatosplenomegaly and poikilocytosis.

In primary myelofibrosis, a progressive scarring (fibrosis) of the bone marrow occurs. As a result, blood forms in sites other than the bone marrow, such as the liver and spleen. This causes an enlargement of these organs. The cause and risk factors are unknown. It commonly occurs in the spent phase of Polycythemia rubra vera, possibly in response to the medication hydroxyurea poisoning the marrow.

Genetics
Genetic associations with JAK2 and MPL have been described.