Myeloproliferative disorders or neoplasms are the groups of medical conditions related to bone marrow and blood. Bone marrow is a spongy tissue present in the bones and performs the function of production of blood cells through stem cell differentiation. However, any mutation in these stem cells leads to neoplasm and there is an increased production of cells. Sometimes the concentration of all the cells increases, while in other times only a single type of cell gets produced. Classification of myelofibrosis is done on the basis of origin.
What Are The Different Types Of Myelofibrosis?
Myelofibrosis is a type of myeloproliferative neoplasm. These neoplasms are related to the bone marrow and the production of blood cells are impacted due to this condition. The cause of such neoplasms is the mutation in the DNA of the blood stem cell. The stem cells abruptly produce either all the cells or a single type of cells which is abnormal. Myelofibrosis is divided into following types on the basis of its origin:
Primary Myelofibrosis- Primary myelofibrosis is the condition in which the disorder occurs on its own and there is no precedence of other myeloproliferative disorders such as polycythemia Vera or essential thrombocythemia. The disease starts in the mutation of the DNA of stem cell leading to increased production of megakaryocytes thus reducing the production of WBC and RBC. These megakaryocytes are primarily responsible for causing scar and fibrosis as they secrete inflammatory mediators.
Secondary Myelofibrosis- Myeloproliferative disorders are the group of diseases related to bone marrow and blood and in almost all the diseases, the concentration of one or all of the blood cells increased. The blood cells produced may either be normal or immature. Secondary myelofibrosis is the condition in which the fibrosis of the bone marrow occurs due to other diseases such as polycythemia vera or essential thrombocythemia. The myelofibrosis occurring, in this case, is the natural fibrotic phase of another disease which leads to myelofibrosis. To differentiate the type of disease that causes secondary myelofibrosis, secondary myelofibrosis is further divided into post-PV myelofibrosis or post-ET myelofibrosis. (1) (2)
Although the origin of the disease is different in primary and secondary myelofibrosis, the symptoms, complications, and treatment of both the conditions are almost similar. (3)
Bone marrow is a type of spongy tissue found in the core of the bones. The primary function of the bone marrow is to produce the blood cells such as RBC, WBC, and platelets. Thus, bone marrow helps in the formation of a significant component of the blood and helps in maintaining the physiological characteristic of blood. The bone marrow consists of stem cells that, on the basis of requirement of the body, differentiate into a different type of cells. For instance, in the case of a low level of oxygen, the number of RBC gets increased while the number of WBC increases in infection. (1)
However, when this spongy tissue is replaced by fibrous scar tissue, the disease is termed as myelofibrosis. In myelofibrosis, abnormal cells and fibrous tissue has increased appearance leading to disruption of normal function of bone marrow. Myelofibrosis is characterized by the presence of a large number of abnormal cells, the megakaryocytes.
These megakaryocytes release an inflammatory mediator, the cytokines that causes inflammation and scar on the bone marrow. Cytokines also increase the fibrous tissue resulting in leaving a very little space for the development of blood cells. This result in anemia as RBC is reduced and increased risk of infection due to the smaller number of WBC.
The people with myelofibrosis are at high risk of developing an aggressive form of cancer, the acute myeloid leukemia.
Myelofibrosis is divided into primary and secondary myelofibrosis. Primary myelofibrosis is the condition which develops on its own due to a mutation in stem cells and no precedence of any other myeloproliferative disorder is found. Secondary myelofibrosis is caused because of a fibrotic phase occurring in other conditions such as polycythemia vera and essential thrombocythemia.