Myelofibrosis (also referred to as agnogenic myeloid metaplasia or idiopathic myelofibrosis) is a serious bone marrow disorder that disrupts your body's normal production of blood cells, which causes extensive scarring in your bone marrow. This in turn leads to severe anemia — causing weakness and fatigue — and enlargement of your spleen and liver — causing abdominal fullness and pain. A rare disease, myelofibrosis can occur at any age, although it most frequently develops after age 50. In most cases, it gets progressively worse. Treatment generally focuses on relieving signs and symptoms and may include medications, blood transfusions, chemotherapy, radiation therapy, and surgery.