Myeloproliferative neoplasms (MPN), previously called myeloproliferative disorders (MPD), are a group of diseases that affect normal blood cell production in the bone marrow. In this case the bone marrow causes an overproduction of one or more blood cell types (red cells, white cells or platelets). Complications arise over time due to the abnormally high number of blood cells that accumulate in the bone marrow and in the circulating blood.

Different types of MPN

There are six different types of MPN. They are generally distinguished from each other by the type of cell which is most affected. These are:

• Polycythemia vera – an overproduction of red blood cells
• Essential thrombocythemia – overproduction of platelets
• Chronic myelomonocytic leukaemia (CMML) – overproduction of white cells (granulocytes)
• Chronic neutrophilic leukaemia – overproduction of neutrophils (a type of white cell)
• Chronic eosinophilic leukaemia – overproduction of eosinophils (a type of white cell)
• Idiopathic myelofibrosis – a condition in which bone marrow tissue is gradually replaced by fibrous scar-like tissue, disrupting normal blood cell production.

In many cases these diseases develop slowly and get worse gradually. In some cases myeloproliferative neoplasms can progress to leukaemia.

Treatment depends on the type of MPN, the severity, general health and age of the person diagnosed. Treatment is generally aimed at reducing excessive number of blood cells in circulation, and at preventing and treating the symptoms and complications of the disease.