What is Myelofibrosis (myelosclerosis)

Myelofibrosis means fibrosis of the bone marrow. In this condition, the marrow becomes fibrous as part of a chronic malignant (cancerous) process in which the proliferation of certain blood cell clones leads to the formation of fibrous tissue. With increased fibrosis of the bone marrow – other organs (spleen, liver) become a source of blood cell synthesis – consequently enlargement of the liver and spleen is the other common finding in myelofibrosis.

Myelofibrosis can occur secondary to other bone marrow conditions (polycythaemia vera, chronic myeloid leukaemia) or as a primary condition – idiopathic myelofibrosis.

The bone marrow is the site of haematopoiesis – i.e. the organ where the blood cells are formed. It is found in the centre of certain long bones (e.g. the femurs or thigh bones), pelvic bones, ribs, sternum etc.

Statistics on Myelofibrosis (myelosclerosis)

Myelofibrosis secondary to other bone marrow diseases is more common than Idiopathic myelofibrosis.

Risk Factors for Myelofibrosis (myelosclerosis)

  • Myelofibrosis can occur secondary to other disorders – such as Polycythaemia vera, or Chronic Myeloid Leukaemia (CML)
  • Idiopathic myelofibrosis is a primary disorder of unknown cause. There is no consistent genetic abnormality. Certain fibrosing growth factors – PDGF and TGFb have been implicated and their source is probably the immature platelet precursors.

Progression of Myelofibrosis (myelosclerosis)

The natural history of idiopathic myelofibrosis is of progressive bone marrow insufficiency with transfusion-dependent anaemia and increasing organomegaly. Patients also become prone to deep infections – e.g. of the lungs. About 10% of patients develop an aggressive form of acute leukaemia.

How is Myelofibrosis (myelosclerosis) Diagnosed?

(1) Anaemia is present. On blood film – poikilocytes and red cells with characteristic tear-drop forms are seen. The presence of immature white cells (myelocytes and promyelocytes) also suggests a myeloproliferative.
(2) The platelet count may be very high, but, in later stages, thrombocytopaenia occurs.
(3) The LAP score is normal or high.
(4) A high serum urate is present.
(5) Low serum folate levels may occur owing to the increased haemopoietic activity.

Prognosis of Myelofibrosis (myelosclerosis)

Patients may survive for 10 years or more, though the range is from 1 to 15. Acceleration of the disease progression occurs in 10-20% of cases from transformation to acute myeloblastic leukaemia. The most common causes of death are cardiovascular disease, infection and gastrointestinal bleeding.

Important prognostic factors include anaemia, thrombocytopaenia (low platelets), age, unexplained fever, weight loss, night sweats, and certain gene abnormalities on bone marrow testing.

How is Myelofibrosis (myelosclerosis) Treated?

Treatment consists of general supportive measures such as:

  • Blood transfusion, folic acid, iron, and pyridoxine for anaemia – but this does not respond to most measures
  • Analgesics for pain. Allopurinol can be used for hyperuricaemia to prevent gouty complications.
  • Drugs such as hydroxycarbamide (most common drug used) and busulfan are used to reduce metabolic activity and high WBC count and platelet levels.
  • Chemotherapy (e.g. with hydroxand radiotherapy are used to reduce splenic size.
  • If the spleen becomes very large and painful, transfusion requirements are high and it may be advisable to perform splenectomy.

Myelofibrosis (myelosclerosis) References

[1] Braunwald, Fauci, Kasper, Hauser, Longo, Jameson. Harrison’s Principles of Internal Medicine. 15th Edition. McGraw-Hill. 2001
[2] Cotran RS, Kumar V, Collins T. Robbins Pathological Basis of Disease Sixth Ed. WB Saunders Company 1999.
[3] Kumar P, Clark M. Clinical Medicine. Fourth Ed. WB Saunders, 1998.