In 2001 the World Health Organization (WHO) listed criteria for the prefibrotic stage of primary myelofibrosis (PMF).


Findings during the prefibrotic stage:

(1) no or mild splenomegaly

(2) no or mild hepatomegaly

(3) mild anemia

(4) mild to moderate leukocytosis

(5) mild to severe thrombocytosis

(6) no or mild leukoerythroblastosis

(7) no or mild poikilocytosis in RBCs

(8) none to few dacryocytes (tear-drop shaped RBCs)

(9) hypercellular bone marrow

(10) megakaryocytic proliferation with atypia

(11) myeloid series proliferation

(12) no to minimal reticular fibrosis



• Atypical changes in megakaryocytes include megakaryocyte clusters, bare nuclei, abnormal nuclear lobulations.


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