Myeloproliferative Neoplasms are a group of three diseases: Essential Thrombocythemia, Polycythemia Vera and Primary Myelofibrosis, which have similar characteristics.
These are chronic diseases characterized by an excess production of red blood cells (red cells), white blood cells (leukocytes) and platelets (cell fragments essential for coagulation) that originate in a blood stem cell located in the bone marrow that acquires an abnormal behavior (usually due to a genetic mutation it acquires), beginning to proliferate uncontrollably.
In simple terms, Essential Thrombocythemia is characterized by an increase in platelet count, Polycythemia Vera by an increase in red blood cells and Primary Myelofibrosis by fibrosis (scarring) of the bone marrow which is usually accompanied by an increase in platelets and leukocytes in the early stages, but often presents with anemia and enlargement of the spleen (splenomegaly) at the time of diagnosis.
Diagnosis of Myeloproliferative Neoplasms
In general, these diseases are diagnosed in a patient without symptoms, when a routine analysis is performed or for other medical reasons and an increase in red blood cells, leukocytes or platelets is detected in the case of Essential Thrombocythemia or Polycythemia Vera, or anemia with enlargement of the spleen in the case of Primary Myelofibrosis.
The hematologist’s first step is to differentiate these abnormal cell increases from secondary or reactive increases in normal blood cells for other reasons. A patient with a chronic respiratory disease, such as emphysema, or even a smoker may have an increase in red blood cells as the body’s physiological compensation for a lack of oxygen in the tissues due to chronic lung disease or smoking. Another example would be the increase in the number of platelets that can be observed as a reactive phenomenon to the lack of iron in a woman with heavy menstruation and in other circumstances such as chronic inflammatory diseases (arthritis). Likewise, an excess of leukocytes is relatively frequent in bacterial infections, in smoking or in patients taking corticosteroids. Therefore, during the first visit, the specialist will try to find out if there are any of these causes that, without being malignant, can produce increases in the number of blood cells.
If a cause for the increase is not evident, hematologists should request some tests to rule out or confirm the existence of any of these diseases. As a practical approach, first of all we ask the patient if he/she has previous analyses in which we can see if this increase or a tendency to it already existed. If the previous analyses were normal and it has been in the last ones in which the increase has been documented in a sustained manner, we suspect that it may be the beginning of a myeloproliferative neoplasm.
The first step carried out is a blood test to detect the existence of mutations associated with these diseases and which correspond to genes called JAK2, Calreticulin (CALR) and thrombopoietin receptor (MPL).
As basic information it should be known that the JAK2 gene mutation, specifically JAK2 V617F is detected in 95%, 60% and 60% of patients with Polycythemia Vera, Essential Thrombocythemia and Primary Myelofibrosis, respectively. In case the detection of the JAK2 V617F mutation is negative, the study of the other mutations is requested if we suspect that the patient may have Essential Thrombocythemia or Primary Myelofibrosis. The presence of any of these mutations does not mean that they are transmitted hereditarily, but that the blood stem cells acquire them for unknown reasons at some point in the patient’s life.
When the result of the genetic analysis confirms the existence of any of these mutations, we must request further tests in order to establish a diagnosis of certainty. The main test used for diagnosis is usually the study of the bone marrow by means of what we call bone marrow aspirate and bone biopsy. Both tests consist of a fine needle puncture of an accessible area of bone (usually in the iliac crest or sternum under local anesthesia) in order to extract a small amount of blood stem cells. Microscopic analysis of the characteristics and percentage of these cells will help us to establish a concrete diagnosis.
Frequently, an abdominal ultrasound is also requested to detect whether the spleen is enlarged, a relatively frequent circumstance, although in a variable percentage, in each of these diseases. With all these data, hematologists apply a series of diagnostic criteria defined by the International Classification of Tumors of the World Health Organization that allow us to confirm the existence of the disease.