Primary myelofibrosis (also known as agnogenic myeloid metaplasia, chronic idiopathic myelofibrosis, myelosclerosis with myeloid metaplasia, and idiopathic myelofibrosis) is characterized by splenomegaly, immature peripheral blood granulocytes and erythrocytes, and teardrop-shaped red blood cells. In its early phase, the disease is characterized by elevated numbers of CD34-positive cells in the marrow, while the later phases involve marrow fibrosis with decreasing CD34 cells in the marrow and a corresponding increase in splenic and liver engorgement with CD34 cells.
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As distinguished from chronic myelogenous leukemia (CML), primary myelofibrosis usually presents as follows:
A white blood cell count smaller than 30,000/mm3.
Prominent teardrops on peripheral smear.
Normocellular or hypocellular marrow with moderate to marked fibrosis.
An absence of the Philadelphia chromosome or the BCR/ABL translocation.
Frequent positivity for the JAK2 mutation.
In addition to the clonal proliferation of a multipotent hematopoietic progenitor cell, an event common to all chronic myeloproliferative disorders, myeloid metaplasia is characterized by colonization of extramedullary sites such as the spleen or liver.[3,4]
Most patients are older than 60 years at diagnosis, and 33% of patients are asymptomatic at presentation. Splenomegaly, sometimes massive, is a characteristic finding.
(Refer to the PDQ summaries on Pain; Fatigue; Fever, Sweats, and Hot Flashes; and Nutrition for information on many of the symptoms listed above.)
The proposed World Health Organization criteria for the diagnosis of primary myelofibrosis requires all three major criteria and two minor criteria.
Presence of megakaryocyte proliferation and atypia, usually accompanied by either reticulin and/or collagen fibrosis; or, in the absence of significant reticulin fibrosis, the megakaryocyte changes must be accompanied by increased bone marrow cellularity characterized by granulocytic proliferation and often decreased erythropoiesis (so-called prefibrotic cellular-phase disease).
Not meeting criteria for polycythemia vera (p. vera), CML, myelodysplastic syndrome, or other myeloid neoplasm.
Demonstration of JAK2 617V greater than F or other clonal marker; or, in the absence of a clonal marker, no evidence of bone marrow fibrosis caused by an underlying inflammatory disease or another neoplastic disease.