yandex rtb 1
ГоловнаЗворотній зв'язок
yande share

Пульмонология, гематология (англ,рус)

·        The risk of bleeding is inversely proportional to the platelet count. When the platelet count is < 50,000/μL, minor bleeding occurs easily and the risk of major bleeding increases. Counts between 20,000 and 50,000/μL predispose to bleeding with trauma, even minor trauma; with counts < 20,000/μL, spontaneous bleeding may occur; with counts < 5000/μL, severe spontaneous bleeding is more likely. However, patients with counts < 10,000/μL may be asymptomatic for years.

 

        Symptoms and Signs

Platelet disorders result in a typical pattern of bleeding: multiple petechiae in the skin, typically most evident on the lower legs; scattered small ecchymoses at sites of minor trauma; mucosal bleeding (epistaxis, bleeding in the GI and GU tracts, vaginal bleeding); and excessive bleeding after surgery. Heavy GI bleeding and bleeding into the CNS may be life threatening. However, massive bleeding into tissues (eg, deep visceral hematomas or hemarthroses) does not commonly occur and suggests a coagulation disorder (hemophilia).

 

Treatment

·        In patients with thrombocytopenia or platelet dysfunction, drugs that further impair platelet function should be avoided, particularly aspirin and other NSAIDs.

·        Patients may require platelet transfusion, but only in limited situations. Prophylactic transfusions are used sparingly because they may lose their effectiveness with repeated use due to the development of platelet alloantibodies.

·        In platelet dysfunction or thrombocytopenia caused by decreased production, transfusions are reserved for active bleeding or severe thrombocytopenia (eg, platelet count < 10,000/μL). In thrombocytopenia caused by platelet destruction, transfusions are reserved for life-threatening or CNS bleeding.

 

Hereditary Intrinsic Platelet Disorders Von Willebrand's Disease

·        Von Willebrand's disease is a hereditary deficiency of von Willebrand's factor (VWF), which causes platelet dysfunction.

·        Von Willebrand's factor (VWF) is synthesized and secreted by vascular endothelium to form part of the perivascular matrix. VWF promotes the platelet adhesion phase of hemostasis by binding with a receptor on the platelet surface membrane (glycoprotein Ib-IX), which connects the platelets to the vessel wall. VWF is also required to maintain normal plasma factor VIII levels.

 

·        Disorders of amplification of platelet activation are the most common hereditary intrinsic platelet disorders and produce mild bleeding. They may result from decreased of adenosine diphosphate  in the platelet granules (storage pool deficiency), from an inability to generate thromboxane A2 from arachidonic acid, or from an inability of platelets to aggregate in response to thromboxane A2.

·        Thrombasthenia (Glanzmann's disease) is a rare autosomal recessive disorder producing a defect in the platelet glycoprotein IIb-IIIa complex; platelets cannot aggregate. Patients may experience severe mucosal bleeding (eg, nosebleeds that stop only after nasal packing and transfusions of platelet concentrates).

·        Bernard-Soulier syndrome is another rare autosomal recessive disorder. It impairs platelet adhesion via a defect in the glycoprotein Ib-IX complex. Bleeding may be severe. Platelets are unusually large. They do not aggregate with ristocetin but aggregate normally with ADP, collagen, and epinephrine.

·        Large platelets associated with functional abnormalities also occur in the May-Hegglin anomaly, a thrombocytopenic disorder with abnormal WBCs, and in the Chédiak-Higashi syndrome

 

Symptoms and Signs of Von Willebrand's Disease

Bleeding manifestations are mild to moderate and include easy bruising; bleeding from small skin cuts that may stop and start over hours; sometimes, increased menstrual bleeding; and abnormal bleeding after surgical procedures (eg, tooth extraction, tonsillectomy).

 

Diagnosis of Von Willebrand's Disease

·        VWD is suspected in patients with bleeding disorders, particularly those with a family history of the disorder.

·        Definitive diagnosis requires measuring total plasma VWF antigen; VWF function, as determined by the ability of the plasma to support agglutination of normal platelets by ristocetin (ristocetin cofactor activity); and plasma factor VIII level.

 

Treatment of Von Willebrand's Disease

·        Patients are treated only if they are actively bleeding or are undergoing an invasive procedure (surgery, dental extraction).

·        Treatment involves replacement of VWF by infusion of pasteurized intermediate-purity factor VIII concentrates which contain components of VWF. These concentrates are virally inactivated and therefore do not transmit HIV infection or hepatitis. Because they do not cause transfusion-transmitted infections, these concentrates are preferred to the previously common use of cryoprecipitate.

·        High-purity factor VIII concentrates are prepared by immunoaffinity chromatography and contain no VWF.

 

Idiopathic Thrombocytopenic Purpura (ITP)

·        Idiopathic (immunologic) thrombocytopenic purpura is a bleeding disorder caused by thrombocytopenia not associated with a systemic disease. Typically, it is chronic in adults but is usually acute and self-limited in children. Spleen size is normal. Diagnosis requires that other disorders be excluded through selective tests.

·        Idiopathic thrombocytopenic purpura (ITP) usually results from development of an antibody directed against a structural platelet antigen (an autoantibody). In childhood ITP the autoantibody may be triggered by binding of viral antigen to megakaryocytes.

 

Symptoms, Signs, and Diagnosis

 

35