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

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.

The disorder usually develops slowly, in people over 50 years old. It leads to progressive bone marrow failure with severe anemia. Low platelet count leads to easy bleeding, and spleen enlargement continues.

• 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 an enlarged spleen. Later in the disease, it may also show an enlarged liver.

• An examination of the blood shows teardrop-shaped red blood cells.
• Bone marrow biopsy may be performed to rule out other causes of the symptoms.
• CBC (complete blood count) shows a low red blood cell count.
• The platelet count is variable.
• The white blood cell count is variable.