Thrombocytopenia is a low level of the clotting cells (thrombocytes or
platelets) in the blood. This results in a reduced
capacity for the blood to clot during injury. In the case of immune
thrombocytopenia, the
platelets are recognised by the immune system as foreign and antibodies are raised against them. Platelets that are tagged with an antibody are then taken out of the blood and destroyed by the spleen and to a certain extent by the liver. Platelets are produced in the bone marrow by cells called megakaryocytes. The platelets are released into the circulation and remain for 8-10 days. However, patients who have immune thrombocytopenia purpura (ITP), have their platelets destroyed by their immune system, in some cases in hours. This form of thrombocytopenia is not to be confused with that caused by certain drugs that can cause bone marrow suppression, such as long term use of anti-inflammatories. Patients with immune thrombocytopenia usually have the chronic form that can go into remission for a length of time but usually recurs.
There is some discrepancy in the literature about when someone is thrombocytopenic. Generally platelet counts are below 100 x 10
9/L for ITP to be diagnosed although some clinicians use 150 x 10
9/L as their cut off point. Often disease severity is only based on platelet count which can be misleading. There are other symptoms that present but not at the same platelet count for all patients. Other symptoms include easy bruising, a flat pin prick rash that doesn’t fade under pressure (petechiae) or a more blotchy rash (purpura) indicating spontaneous micro-bleeds, bleeding gums, heavy and prolonged menstruation in women, and for some patients a persistent fatigue. The haematologist should define a ‘safe’ platelet count for each patient based on when they get symptoms, their lifestyle (i.e. risks of injury) and their age and gender. In patients who have low platelets, the count alone is misleading, as the platelets that are present are younger and have a greater haemostatic activity (i.e. they are more efficient at clotting). Another reason why patients may develop symptoms at a different platelet count depends on where the antibody attaches to the platelet. If the antibody covers a vital part of the platelet, platelet dysfunction can occur which can effectively render the platelet inactive. However, many people live perfectly normal lives with a low platelet count and only require treatment when their platelet counts fall below the ‘safe’ level.
The first line treatment is usually a corticosteroid such as prednisone. These drugs are immunosuppressive and prevent the immune system from attacking the platelets. This is often a successful treatment and can increase platelet counts in as little as 5-7 days. However, the long term use of corticosteroids is usually not recommended and if required regular blood tests are performed to look for adverse affects such as osteopenia (loss of bone mass) and glucose intolerance. Examples of other treatments that are available are anti-D injections (if the patient’s blood group is rhesus positive), splenectomy (removal of the spleen, this is not as commonly used as in the past), immunosuppressants (such as azathioprine, mycophenylate, cyclosporine), B cell depletion (rituximab/rituxan), chemotherapy (vincristine, cyclophosphamide), thrombopoietin receptor agonists (platelet growth factors, e.g. romiplostim) and intravenous infusion of immunoglobulins (IVIG). Each treatment has side effects that need to be weighed up against the patient’s risk of a bleed and any other medical conditions that the patient may have.
This condition can be very scary for those who are newly diagnosed. However, it can be managed and most people still live very full and long lives. If you have just been diagnosed then I highly recommend the Platelet Disorder Support Association website (www.pdsa.org/index.htm). There is a wealth of information available and a forum where you can talk to others who live with the condition.