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

Idiopathic myelofibrosis; Myeloid metaplasia; Agnogenic myeloid metaplasia; Primary myelofibrosis; Secondary myelofibrosis

Bone marrow is the soft, fatty tissue inside your bones. Stem cells are immature cells in the bone marrow that give rise to all of your blood cells. Your blood is made of:

• Red blood cells (which carry oxygen to your tissues)
• White blood cells (which fight infection)
• Platelets (which help your blood clot)

Scarring of the bone marrow means the marrow is not able to make enough blood cells. Anemia, bleeding problems, and a higher risk of infections may occur.

As a result, the liver and spleen try to make some of these blood cells. This causes these organs to swell, which is called extramedullary hematopoiesis.

The cause of myelofibrosis is unknown. There are no known risk factors. The disorder usually develops slowly in people over age 50.

Diseases such as leukemia and lymphoma may also cause bone marrow scarring. This is called secondary myelofibrosis.

Review Date: 06/02/2010
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)