Immune Thrombocytopenia?
Platelets are cells that circulate in the blood to block up leaks in the blood vessels, and prevent bleeding. They are produced in the bone marrow, and the circulating count should be in the range of 150,000 to 450,000.
ITP or Immune Thrombocytopenia is an autoimmune condition, where the body’s immune system misrecognizes the platelets as foreign, latches on to them with an antibody, and the spleen takes them out of circulation. This results in a low circulating platelet count. In adults the cause is mostly unknown, but can be associated with viral infections. Hence, when ITP is diagnosed, one must look for other chronic viral infections, like Hepatitis C or HIV. Another virus that can trigger a transient ITP is EBV.
ITP can manifest with a slightly low count which does not cause any bleeding or bruising, or a severely low count (< 10,000) which can cause spontaneous bleeding from the nose, or mouth, or into the skin, lungs, or even into the brain.
Diagnosis: is now mostly clinical, with a low platelet count, and absence of obvious other factors: enlarged spleen, medications, etc. A bone marrow examination to eliminate other bone marrow diseases, and establish the presence of platelet producing cells (megakaryocytes) is not neccessary initially. It may be required later in the event of a lack of response, i.e. refractory disease.
The treatment depends on the severity of the condition, or urgency of treatment.
Mild, asymptomatic disease may not require any treatment.
If treatment is required, it often starts with
-Steroids as immunosuppressive therapy, to knock off the antibody. Doses are high to begin with, and tapered down. If the counts do not respond, or if the condition relapses after the steroids are tapered down, it is considered steroid resistant.
-Other treatments are tried in serial fashion:
-Intravenous Rituximab
-Low dose mild chemotherapy, e.g. cyclophosphamide, 6-Mercaptopurine, or stronger chemotherapy with intravenous Vincristine
-Danazole is an old androgen drug that can be useful in steroid resistant disease.
When a response is required more urgently:
-Intravenous immunoglobulin is used to saturate the receptors of the culprit antibodies
-Splenectomy, or surgical removal of the spleen. The spleen removes the antibody-platelet combination out of circulation; if the spleen is removed, the complex remains in circulation, and the otherwise functional platelets are available.
For Chronic Refractory ITP, new drugs are available to stimulate the bone marrow, called TPO mimetic drugs. They have had an excellent response when others have failed. The downside is that they are needed to be taken chronically, need to be constantly monitored, and can cause fibrosis in the bone marrow in the long run. If stopped, it can result in severe thrombocytopenia.