Thrombocytopenia

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Thrombocytopenia
Marked thrombocytopenia and fragmented red blood cells.
Image courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology
ICD-10 D69.6, P61.0
ICD-9 287.3, 287.4, 287.5
OMIM 188000 313900
DiseasesDB 27522
MedlinePlus 000586
MeSH D013921

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Thrombocytopenia (or -paenia, or thrombopenia in short) is the presence of relatively few platelets in blood.

Generally speaking a normal platelet count ranges from 150,000 and 450,000 per mm3. These limits, however, are determined by the 2.5th lower and upper percentile, and a deviation does not necessarily imply any form of disease. The number of platelets in a blood sample also decreases rather quickly with time and a low platelet count may be caused by a delay between sampling and analysis.

Signs and symptoms

Often, low platelet levels do not lead to clinical problems; rather, they are picked up on a routine full blood count (or CBC, complete blood count ). Occasionally, there may be bruising, particularly purpura in the forearms, nosebleeds and/or bleeding gums.

It is vital that a full medical history is elicited, to ensure the low platelet count is not due to a secondary process. It is also important to ensure that the other blood cell types red blood cells, and white blood cells, are not also suppressed.

Diagnosis

Laboratory tests might include: full blood count, liver enzymes, renal function, vitamin B12 levels, folic acid levels, erythrocyte sedimentation rate, and peripheral blood smear.

If the cause for the low platelet count remains unclear, bone marrow biopsy is often undertaken, to differentiate whether the low platelet count is due to decreased production or peripheral destruction.

Causes

There are two broad mechanisms of thrombocytopenia: reduced platelet production and increased platelet destruction. Thormbocytopenia is seen in a variety of infectious and genetic disorders as well as a side effect of a large list of phramacotherapies.

Decreased production

Vitamin deficiencies

Hematologic disorders

Reduced thrombopoiesis due to reduced thrombopoietin production

Infectious etiologies

Intrauterine acquired conditions

  • Neonatal alloimmune thrombocytopenia
  • Rubella, congenital
  • Syphilis, congenital

Hereditary syndromes

Chromosomal abnormalities
Mendelian inherited conditions
Autosomal dominant conditions
Autosomal recessive conditions
X-linked inherited conditions
  • GATA1-related cytopenia
  • Immunodysregulation polyendocrinopathy and enteropathy, X-linked
  • Wiskott-Aldrich syndrome
  • X-linked hyperimmunoglobulin M syndrome
  • Mitochondrial genome inherited conditions
  • MELAS


Chemical exposure

Strontium-89

Zinc

Increased destruction

Hematologic Disorders

Cardiovascular causes

Obstetric disorders

Autoimmunde Disorders

Infectious Disorders

  • Dengue fever has been shown to cause shortened platelet survival and immunological platelet destruction
  • HIV [3]

Other disorders

Medication-induced

Thrombocytopenia associated with medications can be due to either a reduction in production of platelets or increased destruction.

Mechanisms

Direct myelosuppression
Immunological platelet destruction
  • Drug binds Fab portion of an antibody. The classic example of this mechanism is the quinidine group of drugs. The Fc portion of the antibody molecule is not involved in the binding process.
  • Drug binds to Fc, and drug-antibody complex binds and activates platelets. Heparin induced thrombocytopenia (HIT) is the classic example of this phenomenon. In HIT, the heparin-antibody-platelet factor 4 (PF4) complex binds to Fc receptors on the surface of the platelet. Since Fc portion of the antibody is bound to the platelets, they are not available to the Fc receptors of the reticulo-endothelial cells, so therefore this system cannot destroy platelets as usual. This may explain why severe thrombocytopenia is not a common feature of HIT.
Heparin-induced thrombocytopenia

(HIT or white clot syndrome): this is a rare but serious condition that may occur in a hospitalized population. The most common clinical setting for HIT is in postoperative coronary artery bypass graft recipients, who may receive large quantities of heparin during surgery. HIT typically occurs about a week after exposure to heparin. The heparin-PF4 antibody complex will activate the platelets, and this can often lead to thrombosis. The term HITT, where the last T stands for thrombosis, denotes the concept that heparin-induced thrombocytopenia often is associated with thrombosis.

List of potential etiologies:

Epiphenomenon

Kasabach-Merritt syndrome Paraneoplastic syndrome


Treatment

Treatment is guided by etiology and disease severity. The main concept in treating thrombocytopenia is to eliminate the underlying problem, whether that means discontinuing suspected drugs that cause thrombocytopenia, or treating underlying sepsis. Diagnosis and treatment of serious thrombocytopenia is usually directed by a hematologist.

Specific treatment plans often depend on the underlying etiology of the thrombocytopenia.

Thrombotic thrombocytopenic purpura (TTP)

Treatment of thrombotic thrombocytopenic purpura is a medical emergency, since the hemolytic anemia and platelet activation can lead to renal failure and changes in the level of consciousness. Treatment of TTP was revolutionized in the 1980s with the application of plasmapheresis. According to the Furlan-Tsai hypothesis [1] [2] , this treatment theoretically works by removing antibodies directed against the von Willebrand factor cleaving protease, ADAMTS-13. The plasmapheresis procedure also adds active ADAMTS-13 protease proteins to the patient, restoring a more physiological state of von Willebrand factor multimers. Patients with persistent antibodies against ADAMTS-13 do not always manifest TTP, and these antibodies alone are not sufficient to explain the how plasmapheresis treats TTP.

ITP

In many cases, ITP is self-limited, and does not require treatment. Platelet counts less than ten thousand per mm3 usually require treatment(less than fifty thousand requires treatment, less than ten thousand is a potentially dangerous situation) and patients with significant bleeding and thrombocytopenia due to ITP are also usually treated. The threshold for treating ITP has decreased since the 1990s, and hematologists recognize that patients rarely bleed with platelet counts greater than ten thousand, though there are documented exceptions to this observation. Treatments for ITP include:

Thrombopoetin analogues have been tested extensively for the treatment of ITP. These agents had previously shown promise but had been found to stimulate antibodies against endogenous thrombopoeitin or lead to thrombosis.

A medication known as AMG 531 was found to be safe and effective for the treatment of ITP in refractory patients. [3] AMG 531 is a peptide that bears no sequence homology with endogenous human thrombopoeitin, so it is not as likely to lead to neutralizing antibodies as previous peptide thrombopoeitin analogues. [4]

Heparin-induced thrombocytopenia and thrombosis (HITT)

Discontinuation of heparin is critical in a case of HITT. Beyond that, however, care must be taken to avoid a thrombosis, and patients started directly on warfarin after a diagnosis of HITT are at excess risk of venous limb gangrene. For this reason, patients are usually treated with a type of blood thinner called a direct thrombin inhibitor such as the FDA-approved lepirudin or argatroban. Other blood thinners sometimes used in this setting that are not FDA-approved for treatment of HITT include bivalirudin and fondaparinux. Platelet transfusions are not a routine component of the treatment of HITT, since thrombosis, not bleeding, is the usual associated problem in this illness.

Congenital amegakaryocytic thrombocytopenia (CAMT)

Bone Marrow/Stem Cell Transplant is the only thing that ultimately cures this genetic disease. Frequent platelet transfusions are required to keep the patient from bleeding to death until transplant is done.

References

  1. ↑ Furlan M, Lämmle B (2001). "Aetiology and pathogenesis of thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome: the role of von Willebrand factor-cleaving protease". Best Pract Res Clin Haematol. 14 (2): 437–54. PMID 11686108.
  2. ↑ Tsai H (2003). "Advances in the pathogenesis, diagnosis, and treatment of thrombotic thrombocytopenic purpura". J Am Soc Nephrol. 14 (4): 1072–81. PMID 12660343.
  3. ↑ Bussel J, Kuter D, George J, McMillan R, Aledort L, Conklin G, Lichtin A, Lyons R, Nieva J, Wasser J, Wiznitzer I, Kelly R, Chen C, Nichol J (2006). "AMG 531, a thrombopoiesis-stimulating protein, for chronic ITP". N Engl J Med. 355 (16): 1672–81. PMID 17050891.
  4. ↑ Broudy V, Lin N (2004). "AMG531 stimulates megakaryopoiesis in vitro by binding to Mpl". Cytokine. 25 (2): 52–60. PMID 14693160.

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