Platelet Disorders - W13 ( Notes) PDF

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TOPIC: Disorders of Primary Hemostasis: Platelet Disorders WEEK 13QUALITATIVE PLATELET DISORDERS Acquired or Congenital disorder of platelet functio n - Excessive bruising and superficial (mucocutaneous) bleeding in a patient whose platelet count is normal  1960s - began rapid progress in underlyi...

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HEMATOLOGY

LECTURE

TOPIC: Disorders of Primary Hemostasis: Platelet Disorders QUALITATIVE PLATELET DISORDERS 

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Acquired or Congenital disorder of platelet function Excessive bruising and superficial (mucocutaneous) bleeding in a patient whose platelet count is normal 1960s - began rapid progress in underlying these disorders, following the development of instruments and test methods for measuring platelet function.

DISORDERS OF PLATELET AGGREGATION (GPIIb/IIIa) I. GLANZMANN THROMBASTHENIA (GT)  Bleeding disorder associated with abnormal in vitro clot retraction and a normal platelet count.  Clot retraction - process by which the volume of a formed clot is reduced through contraction of the intracellular actin-myosin cytoskeleton of activated platelets incorporated in the clot.  Inherited as an autosomal recessive disorder and is seen most frequently in populations with a high degree of consanguinity.  Heterozygotes/Heterozygous - 50% to 60% normal  Homozygotes/Homozygous - serious bleeding problems (Lack surface-expressed GP IIb/IIIa) A. Manifestation: Prolonged bleeding which decreases with age Manifest itself clinically in the neonatal period or infancy (bleeding after circumcision and with epistaxis and gingival bleeding)  Hemorrhagic manifestations include petechiae, purpura, menorrhagia, gastrointestinal bleeding, and hematuria.  The severity of the bleeding episodes seems to decrease with age.  

B. Pathophysiology → deficiency or abnormality of the platelet membrane glycoprotein (GP) IIb/IIIa (integrin aIIbb3) complex → Membrane receptor capable of binding fibrinogen → Von Willebrand Factor (VWF) → Fibronectin → Other adhesives ligands  Binding of fibrinogen to the GP IIb/IIIa complex mediates normal platelet aggregation responses.  Failure of such binding results in a profound defect in hemostatic plug formation and the serious bleeding characteristic of thrombasthenia  Genetic mutations are distributed widely over the ITGA2B and ITGB3 genes present on chromosome 17, which code for GP IIb/IIIa.  GP IIb (αIIb) = megakaryocytes (pro-αIIb)  GP IIIa (β3) = endoplasmic reticulum  Transported to the Golgi apparatus, cleaved to heavy and light chains to form the complete complex.  Uncomplexed aIIb and b3 are not processed in the Golgi body.  Proteins of the GP IIb/IIIa complex must be produced and assembled into a complex in order to be expressed on the platelet surface. SY.ALCANTARA

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 If the GP Iib/IIIa did not form a complex (a iiib & B3) it will not be expressed by the PLT.  B3 MUTATION → Component of vitronectin receptor → Vitronectin - plays a role in vascularization → Unclear pathophysiology C. Classification:  Type 1 - 0-5% of Normal GP IIb/IIIa  Type 2 - 10-20% of Normal; Have more GP IIb/IIIa (Less affected by abnormal clot retraction and fibrinogen binding) D. Laboratory Features: → Normal Platelet Count → Normal Platelet Morphology → Abnormal bleeding time → Abnormal Clot Retraction → ECA (Epinephrine, Collagen, ADP) - Abnormal → Normal Ristocetin → Lack of platelet aggregation in response to all platelet activating agents (adenosine diphosphate ADP, collagen, thrombin, and epinephrine) → Ristocetin-induced binding of VWF to platelets and the resulting platelet agglutination are NORMAL. → Tests for platelet procoagulant activity, such as the platelet factor 3 test, usually show diminished activity, for several reasons. E. Signs and Symptoms:  Thrombasthenia is one of the few forms of platelet dysfunction in which hemorrhage is severe and disabling. Bleeding of all types, including epistaxis, ecchymosis, hemarthrosis, subcutaneous hematoma, menorrhagia, and gastrointestinal and urinary tract hemorrhage F. Treatment:  Platelet Transfusion - for bleeding symptoms  Affected platelets may interfere with transfused platelets → Increase amount of transfusion  Alloimmunization  Hormonal therapy (norothindrone acetate - menorrhagia)  Antifibrinolytic therapy (aminocaproic acid, tranexamic acid - gingival hemmorrhage/excessive bleeding in tooth extraction)  Recombinant factor VIIa (rVIIa; Novoseven, Novo) - surgical and nonsurgical bleeding in patients with GT DISORDERS OF PLATELET ADHESION (GP Ib/IX/V FUNCTION) I. BERNARD-SOULIER (GIANT PLATELET SYNDROME)  Aka Hemorrhagiparous thrombocytic dystrophy  Inherited autosomal recessive disorder  Rare disorder of platelet adhesion  Manifest in infancy or childhood with hemorrhage characteristics of defective platelet function: ecchymoses, epistaxis, and gingival bleeding.  Hemarthroses and expanding hematomas are rarely seen.

HEMATOLOGY

TOPIC: Disorders of Primary Hemostasis: Platelet Disorders  

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GP Ib/IX/V complex is missing from the platelet surface or exhibits abnormal function. Inability to bind to VWF accounts for the inability of platelets to adhere to exposed subendothelium and the resultant bleeding characteristic of this disorder. Resembled defects seen in von Willebrand disease, but this disorder abnormality cannot be corrected by the addition of normal plasma or cryoprecipitate. Heterozygotes - 50% of normal levels of GP Ib, GP V, and GP IX have normal or near-normal platelet function. Homozygotes - enlarged platelets, thrombocytopenia, and usually decreased platelet survival → moderate to severe bleeding disorder A. Pathophysiology

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Four glycoproteins are required to form the GP Ib/IX/V complex: GP Ibα, GP Ibβ, GP IX, and GP V. These proteins are present in the ratio of 2:2:2:1 Surface expression of the GP Ib/IX complex synthesis of GP Ibα, GP Ibβ, and GP IX is required. The most frequent forms of BSS involve defects in GP Ibα synthesis or expression. GP Ibα is essential to normal function because it contains binding sites for VWF and thrombin. Defects in the GP Ibβ and GP IX genes also are known to result in BSS. Missense, frameshift, and nonsense mutation have all been reported. B. Variants

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Several unusual variants of BSS have been described in which the surface expression of the GP Ib/IX/V complex is normal, but its functionality is impaired. Mutations that affect binding domains - impair interactions between elements of the complex, or they result in truncation of a specific protein in the complex, resulting in complexes that fail to bind VWF or ddo so poorly. Antibody to GP Ib/V - cause a Bernard-Soulier-like syndrome (pseudo-BSS) in which the GP Ib/IX/V complex is nonfunctional. Gain-of-function mutation in the GP Ib/IX/V complex result in platelet-type VWD (pseudo-VWD). Such mutations result in spontaneous binding of plasma VWF to the mutated GP Ib/IX/V complex. As a consequence, platelets and large VWF multimers with their associated factor VIII are removed from the circulation, resulting in thrombocytopenia and reduced factor VIII clotting activity.

C. Laboratory Features → Platelet counts - 40,000/μL to near normal → Platelets - 5 to 8 μm in diameter (peripheral blood films) → Normal platelets - 2 to 3 μm in diameter, but they can be as large as 20 μm. → Viewed by Electron Microscopy (platelets contain larger number of cytoplasmic vacoules and membrane complexes, and megakaryocytes exhibit an irregular demarcation membrane system. SY.ALCANTARA

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 BSS platelets have normal aggregation responses to ADP, epinephrine, collagen, and arachidonic acid.  Do not respond to ristocetin (lack of response is due to the lack of GP Ib/IX/V complexed and the inability of BSS platelets to bind VWF)  Have dimished response to thrombin D. Treatment  Antifibrinolytic therapy (mucosal bleeding)  There is no specific treatment for more severe bleeding associated with BSS.  Platelet Transfusions (therapy of choice) but patients invariably develop alloantibodies, limiting further platelet transfusions.  Desmopressin acetate (DDAVP)  Recombinant factor VIIa  BSS patients tend to do better when apheresis platelets are used for transfusion.  Platelets used to treat BSS should be pre-storage leukoreduced to (to reduce alloimmunization)  Antiplatelet therapy SHOULD BE AVOIDED II. INHERITED GIANT PLATELET SYNDROMES  Exhibit large platelets and thrombocytopenia  Thrombocytopenia tends to be mild and bleeding tendency, if present is also mild.  Platelet ultrastructure is generally normal.  Platelets used to treat BSS should be pre-storage leukoreduced to (to reduce alloimmunization) GIANT PLATELETS WITH VELOCARDIOFACIAL SYNDROME  Autosomal recessive      

Platelet count: 100-200 x 109/L Bleeding: NONE REPORTED Velopharyngeal insufficiency, conotruncal heart disease Mild thrombocytopenia Giant platelets GPIβ mapped on chromosome 22q11.2,14

GIANT PLATELEETS WITH ABNORMAL SURFACE GLYCOPROTEINS AND MITRAL VALVE INSUFFICIENCY  Autosomal recessive  Platelet count: 50-60 x 109/L  Mild Bleeding (Ecchymoses, epistaxis)  Mitral valve insufficiency  Giant platelets (20μm)  Absent platelet surface glycoproteins: GP Ia, GP Ic, GP IIa  Normal: GP Ib, GP IIb, and GP IIIa FAMILIAL MACROTHROMBOCYTOPENIA WITH GP IV ABNORMALITY  Autosomal dominant  45 x 109/L to normal  Mild bleeding  Defective GP IV glycosylation  Normal GP IV levels  Early stages of adhesion (mild bleeding tendencies)

HEMATOLOGY

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TOPIC: Disorders of Primary Hemostasis: Platelet Disorders Thrombocytopenia, Giant platelets, variable degree of bleeding disorder) MONTREAL PLATELET SYNDROME  Autosomal dominant  5-40 x 109/L  Significant bruising  Low calpain activity; defective regulation of binding sites for adhesive proteins  Severe thrombocytopenia, giant platelets  Spontaneous platelet aggregation  Large platelets with normal structure

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MAY-HEGGLIN ANOMALY  Autosomal dominant  60-100 x 109/L (thrombocytopenia)  Mild bleeding 

Dohle body-like neutrophil inclusions

FLETCHER SYNDROME  Autosomal dominant  30-90 x 109/L  Deafness, cataracts, nephritis SEBASTIAN SYNDROME  Rare autosomal dominant  40-120 x 109/L  Mild bleeding (epistaxis, possible postoperative hemorrhage  Neutrophil inclusions, giant platelets  EM: Normal platelet ultrastructure HEREDITARY MACROTHROMBOCYTOPENIA     

Autosomal dominant 50-120 x 109/L (mild thrombocytopenia) Mild bleeding (gingival bleeding, epistaxis, easy bruising, menorrhagia) High-frequency hearing loss Giant platelets, presence of glycophorin A on platelet surface

EPSTEIN SYNDROME  Rare autosomal dominant  30-60 x 109/L  Mild bleeding (Epistaxis, GI bleeding, female genital tract)  Nephritis, high-frequency hearing loss, proteinuria  Giant spherical platelets with prominent surface connected canalicular system  Mild bleeding diathesis  Large platelets MEDITERRANEAN MACROTHROMBOCYTOPENIA  89-290 x 109/L (thrombocytopenia)  Stomatocytes in peripheral blood

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DISORDERS OF PLATELET SECRETION  Storage pool and release reaction defects are the most common of the hereditary platelet function defects.  Mucotaneous hemorrhage, hemayuria, epistaxis, spontaneous bruising  Exacerbated by aspirin/antiplatlet agents.  In most of these disorders the platelet count is normal  Platelet aggregation abnormalities are usually seen, but vary depending on the disorder. STORAGE POOL DISEASES  Related to defects of the dense granules or defects of αgranules. Platelet Storage Pool Diseases Dense Granule Deficiencies Hermansky-Pudlak syndrome Chediak-Higashi syndrome Wiskott-Aldrich syndrome Thrombocytopenia-absent radius (TAR) syndrome α-Granule Deficiencies Gray platelet syndrome I. DENSE GRANULE DEFICIENCY  The dense granules are the storage site for serotonin, nucleotides (e.g, ADP and ATP), calcium, and pyrophosphate.  Can be subdivided into deficiency states associated with albinism and those normal individuals (nonalbinos).  Non-albinos - presence of dense granule membrane in normal to near normal numbers (disorder arises from inability to package the dense granules contents.)  Serotonin - accumulates in normal dense granules by an active uptake mechanism. (It also transport mechanisms a nucleotide transporter, MRP4 (ABCC4).  MRP4 (ABCC4) highly expressed in platelets and dense granules has been identified.  Bleeding is usually mild and most often is limited to easy bruising.  The impact of dense granule deficiency can be observed in platelet aggregation tests.  The contents of these granules are extruded when platelet secretion is induced, and secreted ADP plays a major role in platelet activation, recruitment, and aggregation and growth of the hemostatic plug.  Platelet function tests: → Arachidonic acid to platelet-rich plasma fails to induce an aggregation response from platelets with dense granule deficiency → Epinephrine and low-dose ADP induce a primary wave of aggregation, but a secondary wave is missing. → Low concentrations of collagen are decreased to absent. → High concentration of collagen may induce a nearnormal aggregation response. Epinephri ne

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Arachidoni c Acid

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High Collagen

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HEMATOLOGY

TOPIC: Disorders of Primary Hemostasis: Platelet Disorders 

This aggregation pattern, which is nearly identical to the pattern observed in patients taking aspirin, is caused by the lack of ADP secretion.

1. HERMANSKY-PUDLAK SYNDROME  Autosomal recessive disorder  Characterized by: → tyrosinase-positive oculocutaneous albinism → defective lysosomal function in a variety of cell types → ceroid-like deposition in the cells of the reticuloendothelial system → profound platelet dense granule deficiency.  Mutation responsible have been mapped to Chromosome 19  These genes encode for proteins that are involved in intracellular vesicular trafficking and are active in the biogenesis of organelles. A. Manifestations: Bleeding episodes are not severe, but lethal hemorrhage has been reported.  Abnormality consists of marked dilation and tortuosity of the surface-connecting tubular system (the so called Swiss cheese platelet). 

B. Treatment: For extensive surgery or prolonged bleeding both red blood cell (RBC) and platelet transfusions are required.  Thrombin-soaked Gelfoam can be used to treat skin wounds that fail to spontaneously clot.  Oral contraceptives can limit the duration of menstrual periods. 

2. CHEDIAK-HIGASHI SYNDROME  

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Rare autosomal recessive disorder Characterized by: → Partial oculocutaneous albinism → Frequent pyogemic bacterial infections → Giant lysosomal granules in cells of hematologic and nonhematologic origin → Platelet dense granule deficiency → Hemorrhage The disorder is accompanied by severe immunologic defects and progressive neurologic dysfunction in patients who survive to adulthood. The gene for the Chédiak-Higashi syndrome protein is located on Chromosome 1 (1q42.3). A number of nonsense and frameshift mutations result in a truncated Chédiak-Higashi syndrome protein that gives rise to a disorder of generalized cellular dysfunction involving fusion of cytoplasmic granules.

A. Manifestation:  In 85% of patients with Chédiak-Higashi syndrome the disorder progresses to an accelerated phase that is marked by lymphocytic proliferation in the liver, spleen, and marrow with macrophage accumulation in tissues → Pancytopenia worsens → hemorrhage SY.ALCANTARA

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and ever-increasing susceptibility to infection → Death at an early age.  Initially bleeding is increased because of dense granule deficiency and consequent defective platelet function  During the accelerated phase, however, the thrombocytopenia also contributes to a prolonged bleeding tendency.  Bleeding episodes vary from mild to moderate but worsen as the platelet count decreases. 3. WISKOTT-ALDRICH SYNDROME (WAS)  Rare X-linked disease  Caused by mutations in the WAS gene on the short arm of the X Chromosome Xp11.23 that encodes for 502-amino acid protein.  Wiskott-Aldrich syndrome protein WASp (502-amino acid) found in hematopoietic cells and lymphocytes. It plays a crucial role in actin cytoskeleton remodeling. → T cell function is defective due to abnormal cytoskeletal reorganization → Impaired migration → Impaired adhesion → Insufficient interaction with other cells  Disease severity associated with WAS gene mutations ranges from the classic form of WAS with autoimmunity and/or malignancy, to a milder form with isolated microthrombocytopenia (X-linked thrombocytopenia [XLT]), to X-linked neutropenia (XLN).  Approximately 50% of patients with WAS gene mutations have the WAS phenotype, and the other half have the XLT phenotype.  WAS gene mutations causing XLN are very rare.  Homozygous mutations of the WIPF1 gene on chromosome 2 that encodes WASp-interacting protein (WIP) – a cytoplasmic protein required to stabilize WASp – can also cause a WAS phenotype. A. Classification:  Classic form of WAS (eczemathrombocytopenia immunodeficiency syndrome) → characterized by susceptibility to infections associated with immune dysfunction, with recurrent bacterial, viral, and fungal infections, microthrombocytopenia, and severe eczema. → Thrombocytopenia is present at birth, but the full expression of WAS develops over the first 2 years of life. → Lack the ability to make antipolysaccharide antibodies, which results in a propensity for pneumococcal sepsis. → Develop autoimmune disorders, lymphoma, or other malignancies, often leading to early death. → Bleeding episodes are typically moderate to severe.  In WAS a combination of ineffective thrombocytopoiesis and increased platelet sequestration and destruction accounts for the thrombocytopenia.  As with all X-linked recessive disorders, it is found primarily in males. B. Laboratory Features:  Platelets are also structurally abnormal.  Dense granules is decreased

HEMATOLOGY

TOPIC: Disorders of Primary Hemostasis: Platelet Disorders  

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Platelets are small (microthrombocytes) Such small platelets are seen only in association with TORCH (toxoplasma, other agents, rubella virus, cytomegalovirus, herpesvirus) infections. Diminished levels of stored adenine nucleotides are reflected in the lack of dense granules observed on transmission electron micrographs. In laboratory testing the platelet aggregation pattern in WAS is typical of a storage pool deficiency. The platelets show a decreased aggregation response to ADP, collagen, and epinephrine and lack a secondary wave of aggregation in response to these agonists The response to thrombin is normal.

C. Treatment Splenectomy (most effective), which would be consistent with a mechanism of peripheral destruction of platelets.  Platelet transfusions may be needed to treat hemorrhagic episodes.  Bone marrow transplantation also has been attempted, with some success. 

4. THROMBOCYTOPENIA WITH ABSENT RADII SYNDROME  Rare autosomal recessive disorder  Characterized by: → Congenital absence of the radial bones (the most pronounced skeletal abnormality) → Numerous cardiac and other skeletal abnormalities → Thrombocytopenia  Platelets have structural defects in dense granules  Abnormal aggregation responses  Marrow megakaryocytes - decreased in number, immature, or normal. II. ALPHA GRANULE DEFICIENCY (α-granule)  Platelet α-granules - storage site for proteins and is produced by megakaryocyte or present in plasma and taken up by platelets and transported to α-granules for storage.  E.g. Albumin, immunoglobulin G (IgG), and fibrinogen  There are 50 to 80 α-granules per platelet, which are responsible for the granular appearance of platelets on stained blood films. 1. GRAY PLATELET SYNDROME  Rare disorder first described in 1971  Inherited in an autosomal rec...