<B>Myelofibrosis </B>

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Myelofibrosis

Etiology:

• Unknown.

Pathogenesis:

• The mechanism of myelofibrosis is unknown, but is believed to be due to the abnormal proliferation of fibroblasts in response to cytokines (primarily TGF-beta and PDGF) from megakaryocytes.

Epidemiology:

• The disease usually affects inidividuals late in life (sixth through eigth decade).
• Both sexes are equally affected.

General Gross Description:

• The bone reveals a firm, homogeneous, tan to white appearance instead of the normal appearance of red marrow, flecked with bone spicules.

General Microscopic Description:

• Microscopically, the entire marrow space is replaced with mature looking collagen and fibroblasts.
• Megakaryocytes may be seen even in late stages.

Clinical Correlations:

• Clinically, the loss of marrow function in the bone stimulates myelopoiesis in extramedullary sites, such as spleen and liver.
• For this reason, the disease is also known as agnogenic myeloid metaplasia.
• Symptoms may be due to the enlargement of the spleen (a dragging sensation in the left side); or due to the reduction in red and white cell function.
• Sometimes preceded by mylogenous leukemia, or polycythemia vera;often, however, the cause is unknown.
• The prognosis is not good, with relatively few individuals surviving five years.

References:
•Robbins "Pathologic Basis of Disease". (Cotran, Kumar and Robbins, Eds.) 5th Edition. pp 660.