Myelofibrosis, also known as myeloid metaplasia, chronic idiopathic myelofibrosis, and primary myelofibrosis,, is a disorder of the bone marrow, in which the marrow is replaced by fibrous (scar) tissue (collagen).

Myelofibrosis was first described in 1879 and is currently classified as a myeloproliferative disease caused by the growth and proliferation of an abnormal bone marrow stem cell, resulting in the replacement of the bone marrow with fibrous connective tissue.

Signs and symptoms

• Abdominal fullness related to an enlarged spleen
• Bone pain
• Bruising and easy bleeding due to inadequate numbers of platelets
• Fatigue
• Increased susceptibility to infection, such as pneumonia or diarrhea
• Pallor and shortness of breath while doing physical work due to anemia

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 haematopoeisis 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.

Diagnosis

Diagnosis is based upon:

1. Normochromic normocytic anaemia
2. Red cell poikilocytosis on blood film (tear-drop shaped RBCs)
3. JAK 2 mutation on Val 617 Phe locus in 50%
4. Raised levels of lactate dehydrogenase
5. Raised neutrophil alkaline phosphatase score
6. Bone marrow biopsy may show increased cellularity and fibrosis

Treatment

Myleofibrosis has no known cure. Treatment is often challenging and is largely supportive. This may include regular folic acid, allopurinol or blood transfusions. Dexamethasone, alpha-interferon and hydroxycarbamide may play a role. Lenalidomide and Thalidomide may be used in its treatment, though they can cause gout and leave the patient susceptible to diseases such as pneumonia. Frequent blood transfusions may also be required.

Prognosis

Myelofibrosis leads to progressive bone marrow failure. The mean survival is five years and causes of death include infection, bleeding, organ failure, portal hypertension, and leukemic transformation.

Epidemiology

The disorder usually develops slowly, in people over 50 years old.

See also

• Myelophthisic anemia

Notes and references