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Bone Marrow

Perth Haematology :: Dr Steven Ward

Myelofibrosis (MF)


MF is due to  increased fibrous tissue in the marrow, produced by cells in the marrow called fibroblasts and fibrocytes. There is usually a small amount of fibrous tissue in the marrow to act as a framework (or scaffold) for the other haemopoietic cells.


When fibrosis occurs two things can happen:


the marrow and other tissues capable of producing blood (such as the spleen) produce more cells and push these out into the bloodstream earlier than usual. This results in an enlarged spleen, increased blood cell counts (usually granulcoytes and often immature cells, including nucleated red cells)


Once fibrosis is denser often the blood cell counts fall, with anaemia, thrbocytopenia and neutropenia ensuing. The spleen is often quit large.


Fibrosis of the marrow can be:


Primary - MF - no known cause


Secondary - to an underlying disease such as infiltration of the marrow by cancer cells, or rarely lymphoma.



Revised WHO Diagnostic Criteria for MF

Diagnosis requires all 3 major criteria plus 2 minor criteria.


Major Criteria (all required)

1.      Presence of megakaryocyte proliferation and atypia (small to large megas with aberrant n/c ratio and hyperchromatic bulbous or irregularly folded nuclei and dense clustering), usually accompanied by reticulin and/or collagen fibrosis, or in the absence of sugnificant reticulin fibrosis, the meags changes must be accompanied by increased BM cellularity characterised by granulocytic proliferation and often decreased erythropoiesis (ie prefibrotic cellular phase disease)

2.      Not meeting WHO criteria for PRV, CML, MDS or other myeloid neoplasm

3.      JAK2617V>F or other clonal marker, or in the absence of a clonal marker, no evidence of BM fibrosis due to underlying inflammatory or other neoplastic disease.


Minor Criteria (2 required)

1.      Leukoerythroblastosis

2.      Increased LSH

3.      Anaemia

4.      Palpable splenomegay