Symptoms and causes

Symptoms

Myelofibrosis usually develops slowly. In its very early stages, many people don't experience signs or symptoms.

As disruption of normal blood cell production increases, signs and symptoms may include:

  • Feeling tired, weak or short of breath, usually because of anemia
  • Pain or fullness below your ribs on the left side, due to an enlarged spleen
  • Easy bruising
  • Easy bleeding
  • Excessive sweating during sleep (night sweats)
  • Fever
  • Bone pain

When to see a doctor

Make an appointment with your doctor if you have any persistent signs and symptoms that worry you.

Causes

Myelofibrosis occurs when blood stem cells develop a genetic mutation. Blood stem cells have the ability to replicate and divide into the multiple specialized cells that make up your blood — red blood cells, white blood cells and platelets.

It's not clear what causes the genetic mutation in blood stem cells.

As the mutated blood stem cells replicate and divide, they pass along the mutation to the new cells. As more and more of these mutated cells are created, they begin to have serious effects on blood production.

The end result is usually a lack of red blood cells — which causes the anemia characteristic of myelofibrosis — and an overabundance of white blood cells with varying levels of platelets. In people with myelofibrosis, the normally spongy bone marrow becomes scarred.

Several specific gene mutations have been identified in people with myelofibrosis. The most common is the Janus kinase 2 (JAK2) gene. Knowing whether the JAK2 gene or others are associated with your myelofibrosis helps determine your prognosis and your treatment.

Risk factors

Although the cause of myelofibrosis often isn't known, certain factors are known to increase your risk:

  • Age. Myelofibrosis can affect anyone, but it's most often diagnosed in people older than 50.
  • Another blood cell disorder. A small portion of people with myelofibrosis develop the condition as a complication of essential thrombocythemia or polycythemia vera.
  • Exposure to certain chemicals. Myelofibrosis has been linked to exposure to industrial chemicals such as toluene and benzene.
  • Exposure to radiation. People exposed to high levels of radiation, such as survivors of atomic bomb attacks, have an increased risk of myelofibrosis. Some people who received a radioactive contrast material called Thorotrast, used until the 1950s, have developed myelofibrosis.

Complications

Complications that may result from myelofibrosis include:

  • Increased pressure on blood flowing into your liver. Normally, blood flow from the spleen enters your liver through a large blood vessel called the portal vein. Increased blood flow from an enlarged spleen can lead to high blood pressure in the portal vein (portal hypertension). This in turn can force excess blood into smaller veins in your stomach and esophagus, potentially causing these veins to rupture and bleed.
  • Pain. A severely enlarged spleen can cause abdominal pain and back pain.
  • Growths in other areas of your body. Formation of blood cells outside the bone marrow (extramedullary hematopoiesis) may create clumps (tumors) of developing blood cells in other areas of your body. These tumors may cause problems such as bleeding in your gastrointestinal system, coughing or spitting up of blood, compression of your spinal cord, or seizures.
  • Bleeding complications. As the disease progresses, your platelet count tends to drop below normal (thrombocytopenia) and platelet function becomes impaired. An insufficient number of platelets can lead to easy bleeding — an issue that you and your doctor will want to discuss if you're contemplating any type of surgical procedure.
  • Painful bones and joints. Myelofibrosis can lead to hardening of your bone marrow and inflammation of the connective tissue that is found around the bones. This may cause bone and joint pain.
  • Acute leukemia. Some people with myelofibrosis eventually develop acute myelogenous leukemia, a type of blood and bone marrow cancer that progresses rapidly.