Idiopathic thrombocytopenic purpura overview: Difference between revisions
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==Pathophysiology== | ==Pathophysiology== | ||
The exact mechanism of ITP is still not completely understood. However, platelet destruction by antibodies and T-cells as well as impaired megakaryocyte (MK) function seem to play an important role <ref name="pmid28208757">{{cite journal| author=Zufferey A, Kapur R, Semple JW| title=Pathogenesis and Therapeutic Mechanisms in Immune Thrombocytopenia (ITP). | journal=J Clin Med | year= 2017 | volume= 6 | issue= 2 | pages= | pmid=28208757 | doi=10.3390/jcm6020016 | pmc=5332920 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=28208757 }} </ref>. | |||
The antibody mediated destruction of platelets is through the loss of immunological tolerance to the cell surface receptors on platelets. The production of autoantibodies, mainly IgG, target cell surface receptors, mainly GPIIbIIIa and GP Ib/IX, on platelets. These cell surface receptors are also expressed by megakaryocytes which are also impaired in patients with ITP. Targeting by autoantibodies leads to increased phagocytosis of platelets by macrophages in the spleen. The phagocytosis and destruction of platelets leads to a potential increase in cell surface targets by the immune system <ref name="pmid23714309">{{cite journal| author=Kistangari G, McCrae KR| title=Immune thrombocytopenia. | journal=Hematol Oncol Clin North Am | year= 2013 | volume= 27 | issue= 3 | pages= 495-520 | pmid=23714309 | doi=10.1016/j.hoc.2013.03.001 | pmc=3672858 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23714309 }} </ref> <ref name="pmid11919310">{{cite journal| author=Cines DB, Blanchette VS| title=Immune thrombocytopenic purpura. | journal=N Engl J Med | year= 2002 | volume= 346 | issue= 13 | pages= 995-1008 | pmid=11919310 | doi=10.1056/NEJMra010501 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11919310 }} </ref>. This leads to an impairment in thrombopoiesis and a decrease in thrombocyte production. The role of autoantibody production explains the potential benefit of using rituximab, a monoclonal antibody against CD20 antigen on B-cells, in patients who do not respond to initial therapy. However, only 60% of patients with ITP have detectable levels of autoantibodies, suggesting other pathways play an important role in presentation of patients <ref name="pmid23714309">{{cite journal| author=Kistangari G, McCrae KR| title=Immune thrombocytopenia. | journal=Hematol Oncol Clin North Am | year= 2013 | volume= 27 | issue= 3 | pages= 495-520 | pmid=23714309 | doi=10.1016/j.hoc.2013.03.001 | pmc=3672858 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23714309 }} </ref> <ref name="pmid14668642">{{cite journal| author=McMillan R| title=Antiplatelet antibodies in chronic adult immune thrombocytopenic purpura: assays and epitopes. | journal=J Pediatr Hematol Oncol | year= 2003 | volume= 25 Suppl 1 | issue= | pages= S57-61 | pmid=14668642 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14668642 }} </ref> . | |||
Patients with primary ITP tend to have increased levels of IFN-γ and IL-2 with decreased numbers of peripheral Th2+ and Tregs (T-regulatory cells)<ref name="pmid23714309">{{cite journal| author=Kistangari G, McCrae KR| title=Immune thrombocytopenia. | journal=Hematol Oncol Clin North Am | year= 2013 | volume= 27 | issue= 3 | pages= 495-520 | pmid=23714309 | doi=10.1016/j.hoc.2013.03.001 | pmc=3672858 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23714309 }} </ref> <ref name="pmid17067661">{{cite journal| author=Sakakura M, Wada H, Tawara I, Nobori T, Sugiyama T, Sagawa N et al.| title=Reduced Cd4+Cd25+ T cells in patients with idiopathic thrombocytopenic purpura. | journal=Thromb Res | year= 2007 | volume= 120 | issue= 2 | pages= 187-93 | pmid=17067661 | doi=10.1016/j.thromres.2006.09.008 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17067661 }} </ref>. The specific T-regulatory cells decreased in ITP include [CD8+ Tregs; CD4+ Tregs; CD4+CD25+FoxP3<ref name="pmid30015642">{{cite journal| author=Li J, Sullivan JA, Ni H| title=Pathophysiology of immune thrombocytopenia. | journal=Curr Opin Hematol | year= 2018 | volume= 25 | issue= 5 | pages= 373-381 | pmid=30015642 | doi=10.1097/MOH.0000000000000447 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=30015642 }} </ref>. | |||
==Causes== | ==Causes== | ||
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Immune thrombocytopenia(ITP) is autoimmune condition of having a low platelet count (thrombocytopenia) of no known cause (idiopathic)[1]. The major of cases appear to be related to antibodies against platelets. Historically, it is has also been known as immune thrombocytopenic purpura or idiopathic thrombocytopenia purpura[2] Although most cases are asymptomatic, very low platelet counts can lead to a bleeding diathesis and purpura.
Historical Perspective
Classification
- Primary ITP - immune thrombocytopenia as a result for autoimmune antibodies and not related to another identifiable cause/condition of thrombocytopenia[3]. Based on international consensus, it is preferred to avoid the term "idiopathic" and use the term immune to denote this is an antibody-mediated cause[1]. It is also preferred to avoid the use of purpura as the vast majority of cases occur without bleeding/bruising symptoms[1].
- Secondary ITP - immune thrombocytopenia contributed or induced by an associated conditions, such as systemic lupus erythematosus (SLE), autoimmune thrombocytopenia (Evans syndrome), Human Immunodeficiency Virus (HIV), or drug/treatment[3].
| Conditions that cause secondary ITP[3] |
| Systemic lupus erythematosus (SLE), |
| autoimmune thrombocytopenia (Evans syndrome) |
| Human immunodeficiency virus (HIV) |
| Hepatitis C virus (HCV) |
| Helicobacter Pylori |
| Varicella Zoster |
| Antiphospholipid Syndrome |
| Drug-induced immune thrombocytopenia |
In addition to the above classification, ITP can be further characterized by the both the timing of diagnosis and degree of severity[1]:
- Timing criteria:
- Newly diagnosed - Applies to cases within 3 months since diagnosis.
- Persistent - Applies to cases three to 12 months since diagnosis.
- Chronic - Applies to cases more than 12 months since diagnosis.
- Severity:
- Severe ITP - Denotes the presence of any bleeding symptoms which mandate treatment or bleeding which requires additional treatment or change in current treatment (e.g. change in dose) in patient who has previously been stabilized.
Pathophysiology
The exact mechanism of ITP is still not completely understood. However, platelet destruction by antibodies and T-cells as well as impaired megakaryocyte (MK) function seem to play an important role [4].
The antibody mediated destruction of platelets is through the loss of immunological tolerance to the cell surface receptors on platelets. The production of autoantibodies, mainly IgG, target cell surface receptors, mainly GPIIbIIIa and GP Ib/IX, on platelets. These cell surface receptors are also expressed by megakaryocytes which are also impaired in patients with ITP. Targeting by autoantibodies leads to increased phagocytosis of platelets by macrophages in the spleen. The phagocytosis and destruction of platelets leads to a potential increase in cell surface targets by the immune system [5] [6]. This leads to an impairment in thrombopoiesis and a decrease in thrombocyte production. The role of autoantibody production explains the potential benefit of using rituximab, a monoclonal antibody against CD20 antigen on B-cells, in patients who do not respond to initial therapy. However, only 60% of patients with ITP have detectable levels of autoantibodies, suggesting other pathways play an important role in presentation of patients [5] [7] .
Patients with primary ITP tend to have increased levels of IFN-γ and IL-2 with decreased numbers of peripheral Th2+ and Tregs (T-regulatory cells)[5] [8]. The specific T-regulatory cells decreased in ITP include [CD8+ Tregs; CD4+ Tregs; CD4+CD25+FoxP3[9].
Causes
The underlying pathophysiology of ITP involves both
(1) Decreased production of platelets.
(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 (fibrinogen receptor) on the platelet surface. The reason for the development of anti-GPIIb/IIIa antibodies is not very clear but is thought to related 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 precipitate 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 suspected ITP.
Differentiating Idiopathic thrombocytopenic purpura from Other Diseases
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.[10]
Risk Factors
Screening
Natural History, Complications, and Prognosis
Natural History
Complications
Prognosis
Diagnosis
Diagnostic Criteria
History and Symptoms
Physical Examination
Laboratory Findings
Imaging Findings
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
Medical Therapy
Surgery
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.
Secondary Prevention
References
- ↑ 1.0 1.1 1.2 1.3 Rodeghiero F, Stasi R, Gernsheimer T, Michel M, Provan D, Arnold DM; et al. (2009). "Standardization of terminology, definitions and outcome criteria in immune thrombocytopenic purpura of adults and children: report from an international working group". Blood. 113 (11): 2386–93. doi:10.1182/blood-2008-07-162503. PMID 19005182.
- ↑ Bromberg ME (2006). "Immune thrombocytopenic purpura--the changing therapeutic landscape". N Engl J Med. 355 (16): 1643–5. doi:10.1056/NEJMp068169. PMID 17050888.
- ↑ 3.0 3.1 3.2 Swinkels M, Rijkers M, Voorberg J, Vidarsson G, Leebeek FWG, Jansen AJG (2018). "Emerging Concepts in Immune Thrombocytopenia". Front Immunol. 9: 880. doi:10.3389/fimmu.2018.00880. PMC 5937051. PMID 29760702.
- ↑ Zufferey A, Kapur R, Semple JW (2017). "Pathogenesis and Therapeutic Mechanisms in Immune Thrombocytopenia (ITP)". J Clin Med. 6 (2). doi:10.3390/jcm6020016. PMC 5332920. PMID 28208757.
- ↑ 5.0 5.1 5.2 Kistangari G, McCrae KR (2013). "Immune thrombocytopenia". Hematol Oncol Clin North Am. 27 (3): 495–520. doi:10.1016/j.hoc.2013.03.001. PMC 3672858. PMID 23714309.
- ↑ Cines DB, Blanchette VS (2002). "Immune thrombocytopenic purpura". N Engl J Med. 346 (13): 995–1008. doi:10.1056/NEJMra010501. PMID 11919310.
- ↑ McMillan R (2003). "Antiplatelet antibodies in chronic adult immune thrombocytopenic purpura: assays and epitopes". J Pediatr Hematol Oncol. 25 Suppl 1: S57–61. PMID 14668642.
- ↑ Sakakura M, Wada H, Tawara I, Nobori T, Sugiyama T, Sagawa N; et al. (2007). "Reduced Cd4+Cd25+ T cells in patients with idiopathic thrombocytopenic purpura". Thromb Res. 120 (2): 187–93. doi:10.1016/j.thromres.2006.09.008. PMID 17067661.
- ↑ Li J, Sullivan JA, Ni H (2018). "Pathophysiology of immune thrombocytopenia". Curr Opin Hematol. 25 (5): 373–381. doi:10.1097/MOH.0000000000000447. PMID 30015642.
- ↑ 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.