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Primary myelofibrosis is a disorder of the bone marrow, in which the marrow is replaced by fibrous (scar) tissue.

The cause of primary myelofibrosis is unknown. Scarring of the bone marrow causes blood to form in abnormal sites, such as the liver and spleen. This causes swelling of these organs.

There are no known risk factors.

The disorder usually develops slowly in people over age 50.

• Abdominal fullness related to an enlarged spleen
• Bone pain
• Bruising
• Easy bleeding
• Fatigue
• Increased susceptibility to infection
• Pallor
• Shortness of breath while doing physical work

Physical examination shows spleen swelling. Later in the disease, it may also show an enlarged liver.

Tests that may be done include:

• CBC (complete blood count)
• Platelet count

An examination of the blood shows teardrop-shaped red blood cells. Bone marrow biopsy may be done to rule out other causes of the symptoms.

There is no specific treatment for primary myelofibrosis. The goal of treatment is to relieve symptoms. Treatment may involve:

• Blood transfusions to correct anemia
• Radiation and chemotherapy
• Medicines called recombinant erythropoietin or androgens to help stimulate red blood cell production
• Splenectomy (removal of the spleen) if swelling causes symptoms

In young people, bone marrow transplants appear to improve the outlook.

This disorder causes slowly worsening bone marrow failure with severe anemia. Low platelet count leads to easy bleeding, and spleen swelling may slowly get worse.

The average survival of people with primary myelofibrosis is about 5 years. However, many people survive for decades.

• Acute myelogenous leukemia
• Liver failure

Call for an appointment with your health care provider if symptoms of this disorder develop. Uncontrolled bleeding, shortness of breath, jaundice, and confusion that gets worse require urgent or emergency care.

There is no known prevention.

Myelofibrosis; Idiopathic myelofibrosis; Myeloid metaplasia; Agnogenic myeloid metaplasia

Hoffman R, Benz Jr. EJ, Shattil SJ, et al. Hematology: Basic Principles and Practice. 4th ed. Philladelphia, Pa: Churchill Livingston; 2005.

McPherson RA and Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: WB Saunders; 2007:561-62.

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and James R. Mason, MD, Oncologist, Director, Blood and Marrow Transplantation Program and Stem Cell Processing Lab, Scripps Clinic, Torrey Pines, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.