Idiopathic thrombocytopenic purpura overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Idiopathic thrombocytopenic purpura (ITP) is the condition of having a low platelet count (thrombocytopenia) of no known cause (idiopathic). As most causes appear to be related to antibodies against platelets, it is also known as immune thrombocytopenic purpura. Although most cases are asymptomatic, very low platelet counts can lead to a bleeding diathesis and purpura.
Causes
The underlying pathophysiology of ITP involves both (1) decreased production of platelets and (2) increased destruction of platelets. Regarding the latter mechanism, this is thought to be due to B cells producing IgG, which binds to GPIIb/IIIa (fibriogen receptor) on the platelet surface. The reason for the development of anti-GPIIb/IIIa antibodies is not very clear but is thought to relatd to immune or infectious phenomena. Immune etiologies involves loss of self-tolerance, whereby the body produces antibodies against its own cells. Immunosuppressive hematological conditions can preciptiate this. These include CLL, APLS, SLE, and Evan's syndrome. Infectious agents that can lead to development of anti-platelet antibodies include HIV, hepatitis C and H. pylori. Molecular mimicry between infectious agents and platelets leads to the development of the antibodies. It is important to evaluate for these etiologies in patients with sspected ITP.
Epidemiology and Demographics
The incidence of ITP is 5-10 new cases per 100,000 per year, with children accounting for half of that amount. The male:female ratio in the adult group is 1:1.2–1.7 (for children it is 1:1) and the median age of adults at the diagnosis is 56–60.[1]
Diagnosis
Other Diagnostic Studies
A bone marrow examination may be performed on patients over the age of 60 and people who do not respond to treatment, or when the diagnosis is in doubt. The bone marrow biopsy in ITP can show increased (thought not always) megakaryocytes, bizarre giant platelets and platelet fragments. (Large platelets are often seen in the peripheral blood smear though this can be seen in other diseases.) When the spleen is removed it may show increased lymphatic nodularity.
Treatment
Radiation
Splenic radiation (RT) is usually given for steroid-resistant ITP. One to six weeks of 75-1370 cGy with or without concomittant post-RT steroids. Patients can respond for >1 year. It is a safe alternative for patients too old for splenectomy.
Primary Prevention
The causes and risk factors are unknown, except in children when it may be related to a viral infection. Prevention methods are unknown.
References
- ↑ Cines DB, Bussel JB (2005). "How I treat idiopathic thrombocytopenic purpura (ITP)". Blood. 106 (7): 2244–51. doi:10.1182/blood-2004-12-4598. PMID 15941913.