Lecture 4, fall 2014 pdf

Lecture 4

Disorders of Primary Hemostasis: Quan7ta7ve Platelet Disorders

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Disorders of Primary Hemostasis

•  Abnormali7es that result in bleeding due to defects in forma7on of the primary hemosta7c (platelet) plug

•  Defect in the ability of platelets to adhere to the vascular endothelium –  Platelet aggrega7on is normal

•  Defects in primary hemostasis are classified as –  Qualita7ve defects –  Quan7ta7ve defects

•  Present as –  Acquired defects

•  Bleeding episodes usually do NOT present un7l adulthood –  Congenital defects

•  Bleeding episodes present during early childhood

•  Purpura—refers to petechiae and ecchymoses •  Easy bruisability—too many petechiae and ecchymoses—less than “usual” trauma •  Excess bleeding—Involves both platelets and coagula7on abnormali7es

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Clinical Manifesta7ons

•  Petechiae –  Small red to purple spots in the skin, [<3 mm] –  Blood leaking from the endothelial capillary lining –  Occur on the extremi7es due to high venous

pressure –  Manifest as platelet and blood vessel

abnormali7es •  Ecchymoses

–  Bruises [>3 mm] –  Caused by blood escaping through the

endothelium and into intact subcutaneous 7ssue—come from vessels larger than a capillaries

–  Red to purple ini7ally à turn yellowish green as they heal

–  Found in defects involving blood vessels, platelet, and coagula7on proteins

•  Hematoma –  Blood leaks from a vessel and collects in the intact

skin –  Blue or purple and slightly raised –  Can occur in organs and 7ssues –  May be in the form of a clot

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Quan7ta7ve Platelet Disorders •  Thrombocytopenia

–  Clinical symptoms typically not seen un7l <100 X 109/L •  More o"en <50 X 109/L •  Spontaneous bleeding occurs <20 X 109/L •  Life-‐threatening <10 X 109/L

–  Clinical Manifesta7on Ø  Petechiae Ø Menorrhagia Ø  Spontaneous bruising Ø  Fatal bleeding into the CNS may occur Ø  Spontaneous bleeding in GI-‐tract, GU-‐tract and nose Ø  Prolonged BT but Normal coagula.on tests

•  Due to 1.   Deficient platelet producCon 2.   Abnormal platelet distribuCon (splenic sequestraCon) 3.   Increased destrucCon

•  Secondary to an underlying disease •  Most common cause of excess or abnormal bleeding

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Mechanisms of Thrombocytopenia 1.  Decreased Produc7on

A.  Megakaryocy7c hypoplasia B.  Replacement of normal

marrow Ø  Tumor cells

(Myelophthisic picture) Ø  Fibrosis

C.  Ineffec7ve thrombopoiesis

2.  Abnormal Platelet Distribu7on A. Dilu7onal thrombo-‐

cytopenia B.  Increased splenic

sequestra7on

3.  Increased Destruc7on A.  Immune B.  Nonimmune

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Mechanism of Destruc7on

•  Immunologic causes –  Alloan7bodies –  Autoan7bodies –  Drug-‐induced an7bodies –  Isoan7bodies

•  Non-‐immunologic causes –  DIC –  TTP –  HUS –  Microangiopathy –  Vasculi7s

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1.  Result in hemorrhagic diathesis

2.  Presence of schistocytes

Immune-‐mediated causes occur more frequently

Immune-‐Mediated Destruc7on •  Group of thrombocytopenias in which an immune-‐mediated mechanism causes increased destruc7on of

platelets •  Two types immune-‐mediated destrucCon

1.  Primary (Idiopathic) –  Defects that are intrinsic to the platelet

2.  Secondary –  Defect that is extrinsic to the platelet

Ø  Due to an underlying disease

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Immune Mediated Destruc7on

•  Caused by anCbodies – analogous to immune-‐mediated destruc7on of RBC’s

•  Platelets become sensi7zed with an7body •  Mononuclear phagocytes destroy these an7body-‐

coated platelets in the spleen •  Monocytes (macrophages) have Fc receptors that they

use to recognize à platelets that are coated with an7body

–  Leads to decreased survival 7me in circula7on (2-‐3 days)

•  An7bodies abach to platelets by their Fab regions to either 1.  GPIIb/IIIa 2.  GPIb/IX 3.  Nonspecifically to immune complexes via FcγRIIA

•  Monocytes recognize platelets coated with IgG, IgM, IgA, and complement

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Immune Thrombocytopenia Immune Thrombocytopenic Purpura—ITP

•  ITP (autoimmune thrombocytopenia) – autoimmune disorder characterized by •  (1) Immune-‐mediated destrucCon of platelets •  (2) impaired platelet producCon

•  Autoan7bodies – mostly IgG – directed against GPIIb/IIIa, GPIb/IX, GPV

•  One of the most common disorders causing severe isolated thrombocytopenia –  Most cases à asymptoma7c –  Low platelet counts can lead to a bleeding diathesis and purpura –  There is no specific test that readily confirms the diagnosis of ITP à therefore it is a diagnosis

of exclusion –  An7platelet an7bodies + BM examina7on + Clinical presenta7on

•  Two types ITP 1.  Acute ITP 2.  Chronic ITP

•  50-‐100 new cases per million per year, with children accoun7ng for half of that amount •  Clinical features

Ø  Bruising, Petechiae, Epistaxis, Gingival bleeding Ø  Thrombocytopenia (platelet count is below 30,000) Ø  hbp://www.itpscience.com/regula7on_platelet_produc7on/itp_video.html 9

Pathology of ITP 1.  A trigger for platelet destruc7on is

the produc7on of ITP autoanCbodies

2.  An7bodies to the platelet glycoprotein IIb/IIIa complex bind to platelets and leading to phagocytosis by re7culo-‐endothelial macrophages via Fc receptors

3.  The platelet proteins are degraded and displayed on the macrophage cell surface in a complex with CD154

•  CD154 = CD40 LIGAND à it binds to CD40 on APCs

4.   Macrophages à s7mulate T-‐cell–mediated an7body produc7on by B cells

5.  The resul7ng autoanCbodies perpetuate platelet destrucCon

Acute ITP •  E7ology

–  Post-‐viral infec7on in children 1-‐7 years of age –  Generally lasts <6 months –  Affects males and females equally

•  Pathophysiology –  Commonly preceded by a previous viral infec7on or immuniza7on

•  HIV, rubella, rubeola, varicella, mumps, EBV, and CMV 1.  [An.bodies/an.body complexes] are produced during viral infecCon and they

complexes abach to the platelet surface 2.  The [platelet + an7body complexes] are removed by macrophages in spleen 3.  Autoan7bodies are produced against ABs directed against viral or bacterial an7gens that

cross-‐react with platelets a.  Autoan7bodies result from the persistence of pro-‐inflammatory cytokines and the

s7mulated T-‐cell response à following a viral or environmental trigger b.  This s.mulated response leads to the emergence of previously suppressed

autoanCbodies

•  Key pathology—failure to suppress these autoanCbodies a.  May be caused by CD25+ T-‐regulatory cells which are not fully mature in

young children à therefore these autoan7bodies are produced

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Chronic ITP •  E7ology

–  Unknown; adults 20 -‐ 50 years of age –  Insidious onset with lack of a previous vial infec7on –  Female-‐to-‐male ra7o = 1.7:1 –  Median age 38-‐49 –  Spontaneous remission is uncommon –  Persistent thrombocytopenia las7ng more than 6-‐12 months to years –  An7platelet an7bodies found in 58-‐80% of pa7ents

•  Signs and Symptoms –  Petechiae, ecchymoses, epistaxis, menorrhagia, gingival bleeding, hematuria, absence of

splenomegaly –  Treat if platelet count drops <30,000

•  Pathophysiology –  Autoan7bodies (IgG) produced against platelet an7gens à platelet-‐an7body complexes

removed by macrophages in spleen –  Helicobacter pylori infec7ons have been suggested to be involved in chronic ITP

•  43-‐75% of pa7ents with chronic ITP have H. pylori à eradica.on of H. pylori with an.bio.cs improves situa.on

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Comparison of Acute versus Chronic ITP

Feature Acute ITP Chronic ITP

Peak age Children – 2-‐4 years Adults – 20-‐40 years

Platelet count (ini7al) <20 x 109/L 30-‐80 x 109/L

Onset Abrupt Insidious

Antecedent infec7on Common – 1-‐3 weeks Unusual

Spontaneous remission ~93% of cases Rare Course of disease fluctuates

Therapy 1.  Cor7costeroids 2.  An7-‐D 3.  IVIg

1.  Cor7costeroids 2.  Splenectomy

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Laboratory Findings in ITP Peripheral blood 1.  Decreased platelet count on peripheral blood smear 2.  Megathrombocytes (large platelets) on peripheral blood smear 3.  Other CBC parameters within reference range

Bone marrow 1.  Megakaryocytes are normal to increased in the bone marrow

–  Autoan7bodies may interfere with platelet produc7on or platelet release from the bone marrow

–  Suppression of megakaryocyte produc7on by autoan7bodies may be associated with increased apoptosis in adult ITP (ineffec7ve thrombopoiesis)

2.  Thrombopoie7n levels are normal or slightly increased in some ITP pa7ents resul7ng in normal to increased megakaryocytes

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Lab Findings in ITP

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Normal PB ITP PB Bone Marrow

Petechiae Purpura

Treatment of ITP •  Treatment

–  When PLTs <30 x 109/L •  Steroid therapy; if ineffec7ve •  Intravenous an7-‐D (in Rh posi7ve pa7ents)

–  Interacts with the an7body-‐coated RBCs – the macrophages are busy destroying RBCs and leave the platelets alone – hemolysis is common

•  IVIG –  Saturates the Fc receptors on macrophages blocking them from binding to AB-‐coated platelets

•  Splenectomy in pa7ents refractory to the above •  Platelet transfusion if severe hemorrhage

–  Cor7costeroids are the treatment of choice –  Followed by splenectomy if refractory to cor7costeroids –  Newer therapies

•  An7CD20+ (Rituximab) •  An7-‐CD40+

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Regula7on of Platelet Produc7on

•  TPO is produced in the liver •  Inflamma7on and thrombocytopenia

enhance TPO produc7on •  Platelets have high affinity TPO

receptors and remove TPO from the circula7on

•  Free plasma thrombopoie7n binds to megakaryocytes à s.mula.on of megakaryocytopoiesis

The molecular mechansims that control hematopoesis. JCI. 2005.

Thrombopoie7n-‐Receptor Agonists for Primary Immune Thrombocytopenia NEJM. 2011

•  Eltrombopag –  Oral thrombopoie7n (TPO)

receptor agonist –  Interacts with transmembrane

domain of human TPO receptor –  Induces megakaryocyte

prolifera7on and differen7a7on from bone marrow progenitor cells

•  Romiplos7m –  An Fc-‐pep7de fusion protein

(pep7body) –  Increases platelet produc7on

through binding and ac7va7on of the thrombopoie7n (TPO) receptor – similar mechanism to endogenous TPO

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Other Causes of Thrombocytopenia •  ITP in Pregnancy

–  Gesta7onal thrombocytopenia –  Benign condi7on

•  Platelet count returns to normal within 12 weeks post-‐delivery •  If the diagnosis is made during pregnancy à IVIG and steroid therapy may be used •  An7body-‐related platelet destruc7on occurs in females previously immunized –most

pa7ents are mul7parous •  An7bodies are directed against platelet an7gen PLA-‐1A (HPA-‐1a)

•  Post-‐Transfusion Purpura –  Rare form of alloimmune thrombocytopenia characterized by severe thrombocytopenia and

bleeding à following TRANSFUSION of blood or blood products –  Caused by anCbody-‐related platelet destrucCon in previously-‐immunized pa7ents –  An7bodies are directed against platelet an7gen PLA-‐1a (HPA-‐1a) in most cases –  Severe thrombocytopenia occurs ~3-‐12 days following transfusion –  Diagnosis of PTP made by detec;ng an;bodies against platelet-‐specific an;gens in the

pa;ent’s serum

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Other Causes of Thrombocytopenia

•  Neonatal Alloimmune Thrombocytopenia (NAITP) –  Caused by fetal-‐maternal incompa7bility of platelet an7gens –  Maternal an7bodies cross the placenta causing destruc7on of the fetal

platelets –  First pregnancy affects 50% of cases –  Offending an7body is an7-‐HPA-‐1a and is an IgG alloan7body (75% of cases)

•  These are also directed against gpIIb/IIIa, Ib/IX, Ia/IIa, and CD109 •  In whites 97.5% of the an7bodies are against gpIIb/IIIa

–  Affected neonate is treated by transfusion of an7gen-‐compa7ble platelets or washed maternal platelets

•  Congenital MegakaryocyCc Hypoplasia –  Decrease in bone marrow megakaryocytes

1.  Thrombocytopenia with Absent Radii (TAR) 2.  Wiskob-‐Aldrich Syndrome (WAS) 3.  May-‐Hegglin Anomaly (MHA)

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Thrombocytopenia Due to Impaired Platelet Produc7on •  Thrombocytopenia with absent radii

(TAR) –  Characterized by

A.  Neonatal thrombocytopenia and B.  Hypoplasia of the radial bones of

the forearms with absent, short, or malformed ulnae

1.  Impaired DNA repair that results from a fetal injury about 8 weeks gesta7on

2.  Pa7ents have 90% incidence of leukemoid reac7ons with WBC counts exceeding 100,000/ μL

3.  Platelet counts range from 10,000-‐30,000/μL

4.  A failure in produc7on of humoral or cellular s7mulators of mega-‐karyocytopoiesis

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May-‐Hegglin Anomaly •  Characterized by various degrees of thrombocytopenia •  May be associated with

1.  Purpura and bleeding 2.  Giant platelets (20 μm in diameter) containing few granules 3.  Large (2-‐5 µm basophilic cytoplasmic inclusion bodies in granulocytes that resemble

Döhle bodies •  Otherwise normal platelet morphology and func7on •  Muta7on in the MYH9 gene present in chromosomal 22

–  A cytoskeletal protein in platelets that may be responsible for the abnormal platelet diameter

•  Most pa7ents have no bleeding episodes unless thrombocytopenia is severe

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Wiskob-‐Aldrich Syndrome •  Wiskob-‐Aldrich syndrome is an immune deficiency disorder in which there is a

decreased produc7on of IgM •  WAS is characterized by

1.  Thrombocytopenia with small platelets (microthrombocytes) 2.  Eczema 3.  Increased risk of developing an autoimmune disorder or cancer 4.  Associated with a defec7ve gene on the X chromosome

•  Females tend to be carriers of the syndrome •  Males have the defec7ve gene and develop symptoms

•  X-‐linked mode of transmission –  DefecCve protein called WASp (Wiskod-‐Aldrich syndrome protein) whose

expression is limited to cells of hematopoie7c lineage

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Thrombocytopenia due to Ineffec7ve Thrombopoiesis

•  Associated with normal to increased marrow cellularity but peripheral blood cytopenias 1.  Megaloblas7c anemia à associated with

a.  Vitamin B12 or folate deficiency b.  Thrombocytopenia results from impaired DNA synthesis c.  Lactate dehydrogenase (LD) levels are elevated due to intra-‐

medullary death of hematopoie7c progenitors 2.  Myelodysplas7c syndromes may simulate vitamin deficiency and do

not respond to vitamin replacement therapy 3.  Alcohol has direct toxic effect on the marrow à induces folic acid

and/or vitamin B12 deficiency •  Thrombocytopenia is mild with normal platelet life span

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Drug-‐Induced Thrombocytopenia •  Rela7vely common—more than 200 drugs have been reported •  hbp://w3.ouhsc.edu/platelets •  Symptoms 6-‐7 days azer administra7on •  Platelet count is extremely low (<10 x109/L) •  Petechiae, purpura, and occasionally intracranial bleeding •  Treatment involves removal of the offending drug

•  Three pathways to explains drug-‐induced immune-‐mediated platelet destruc7on 1.   Hapten theory

•  Small molecule that can elicit an immune response ONLY when abached to a large carrier protein

•  The drug (carrier protein) binds covalently to platelets à [drug-‐platelet anCgenic complex] -‐-‐ the drug acts as a hapten

2.   Innocent bystander mechanism •  The drug binds to a specific anCbody and elicits an immune response •  An7body binding to the [drug-‐protein complex ]forms an immune complex that

nonspecifically binds to circula7ng platelet Fc receptors 3.   Drug-‐dependent anCbodies

•  An7bodies are created against an epitope(s) created by the associaCon of the drug with proteins on the platelet surface

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Hapten Theory •  Small molecule that can

elicit an immune response ONLY when abached to a large carrier protein

•  The drug (carrier protein) binds covalently to platelets à [drug-‐platelet anCgenic complex] -‐-‐ the drug acts as a hapten

hbp://classes.midlandstech.edu/carterp/Courses/bio225/chap19/19-‐05_Thrombocyto_1.jpg26

Varia7ons in An7body Binding to Platelets •  A—Platelet autoan7bodies or allo-‐

an7bodies –  Bind to epitopes of GPIIb/IIIa, GPIb/

IX

•  B—Quinine/Quinidine-‐dependent an7bodies –  Bind to a complex of drug and

glycoprotein –  GPIIb/IIIa or GPIb/IX

•  C—Heparin-‐dependent an7bodies –  Heparin binds to PF4 and the

heparin:PF4 complex binds to IgG an7heparin an7bodies via the Fab of the an7body

–  The Fc por7on of the an7body binds to platelet IgG FCγIIa receptors

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Condi7ons with Mul7ple Mechanism of Thrombocytopenia

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Alcoholism 1.  In alcoholic pa7ents without cirrhosis the

major effect is ethanol. a.   Ethanol directly suppresses MGK

producCon. b.   Causes folate deficiency.

2.  In pa7ents with cirrhosis the major effect is due to under produc7on of coagula7on factors by the liver.

1.  Suppress platelet produc7on 2.  Ineffec7ve platelet produc7on 3.  Increased destruc7on 4.  Splenomegaly

Lymphoprolifera7ve Disease 1.  Impaired produc7on 2.  Immune destruc7on 3.  Splenomegaly

Cardiopulmonary Bypass Surgery

1.  Mechanical destruc7on 2.  Increased u7liza7on 3.  Dilu7onal thrombocytopenia

•  10 or more units of blood 4.  Inadequate neutraliza7on of heparin

Thrombo7c Microangiopathies (TMA)

•  Group of disorders characterized by – Microangiopathic hemoly7c anemia –  Thrombocytopenia – Microvascular thrombosis

•  Subtypes TMA –  Thrombo7c thrombocytopenic purpura (TTP) –  Hemoly7c uremic syndrome (HUS)

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End organ damage

Thrombo7c Thrombocytopenic Purpura •  Congenital – Upshaw-‐Shulman syndrome

–  Characterized by repeated episodes of thrombocytopenia and microangiopathic hemoly7c anemia during early childhood

–  Moake (1982) described unusually large vWF mul7mers in the plasma of pa7ents with TTP

•  Proposed that a lack of a “cleaving protease” was responsible •  Congenital deficiency of ADAMTS-‐13 – disintegrin-‐like and metalloprotease with

thrombospondin type 1 mo.f

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Brass, L, 2001, Nature Med 7:1177-1178.

Thrombo7c Thrombocytopenic Purpura

•  Acquired – Idiopathic TTP –  Involves an autoimmune mechanism à acquired absence of ADAMTS13

ac7vity –  Usually associated with autoan7body – IgG inhibitor of the protease –  Extremely rare in pa7ents without a thrombo7c microangiopathy

•  With the possible excep.on of sepsis

•  Secondary TTP –  Mechanisms poorly understood –> levels of ADAMTS13 ac7vity generally not

as depressed as in idiopathic –  Comprises ~40% of cases of TTP –  Predisposing factors

•  Cancer •  BMT •  Pregnancy •  Medica7ons •  HIV infec7on

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vWF •  Large mul7meric protein – ranges from 600 kD to > 20 million kD

–  Synthesized by endothelial cells and megakaryocytes •  Endothelial cells source of plasma vWF

–  Released from the endothelial cells as mature vWF azer cleavage of a propep7de –  vWF-‐cleaving protease cleaves the ULvWF into inac7ve monomers to prevent interac7on with

platelets

•  Func7on of vWF 1.  Supports platelet adhesion and ac7va7on at sites of vascular injury:

a.  vWF binds extravascular collagen b.  Platelets adhere to bound vWF

2.  Supports coagula7on mechanism: a.  vWF protects FVIII in circula7on b.  vWF co-‐localizes FVIII at sites of vascular injury

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Platelets

Coagula7on Proteins Endothelium

vWF

Synthesis of vWF

•  Steps in synthesis of vWF 1.  First synthesized as a pro-‐vWF monomer 2. Dimeriza.on occurs in ER 3.  Pro-‐vWF monomers linked together at the carboxyl terminal end 4.  Dimeric molecules pass to the Golgi apparatus 5.  Dimers mul.merize 6.  Propep7de is cleaved off à mature subunit

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Blood 79:2507

Prog Heamtol 9:233

Func7on of ADAMTS 13

•  ADAMTS-‐13 abaches to binding sites on the endothelial cell surfaces

–  ADAMTS-‐13 abaches to endothelial surface via à a thrombospondin-‐1-‐like domain – RGD (arginine/glycine/aspartate)

•  Cleaves ULvWF as they are secreted by

the s7mulated endothelial cells

•  Smaller vWF forms that circulate azer cleavage do not induce the adhesion and aggrega7on of platelets during normal blood flow

Func7on of ADAMTS 13

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•  Absent or severely reduced ac7vity of ADAMTS-‐13 prevents cleavage of ULvWF as they are secreted by endothelial cells

•  The uncleaved mul.mers induce adhesion and aggrega7on of platelets in flowing blood

•  Due to: –  Congenital or acquired deficiency of

ADAMTS-‐13

•  Note: –  Interference with the aWachment of

ADAMTS-‐13 to endothelial cells in vivo à may also cause TTP in pa.ents with normal ADAMTS-‐13 ac.vity in plasma

Pathology of TTP

•  Classic pentad of features 1.  Microangiopathic hemoly7c

anemia 2.  Thrombocytopenia 3.  Neurologic symptoms 4.  Kidney failure 5.  Fever

•  Affects kidneys, heart, and brain with small arteriolar thrombi

•  TTP overlaps with hemoly7c uremic syndrome (HUS) that may be precipitated by verotoxins from such organisms as E. coli (type O157:H7) à endothelial injury

hbp://library.med.utah.edu/WebPath/RENAHTML/RENAL030.html

Glomerulus

BV with onion-‐skinning (thromboCc microangiopathy) Curr Opin Nephrol Hypertens 19 (3): 242-‐7

Hemoly7c Uremic Syndrome—HUS

•  Thrombo7c microangiopathy that mainly affects children

•  Characterized by a Tetrad of clinical findings 1.  Hemoly.c anemia with RBC fragmenta.on 2.  Acute renal failure 3.  Thrombocytopenia 4.  Variable CNS involvement

•  Associated with a.  Upper respiratory infec.on b.  Urinary tract infec.on c.  Viral disease such as varicella or measles

•  Generally encompasses several diverse disorders

–  Typical form 1.  Associated with diarrhea caused by verotoxin-‐producing E. coli

–  ~95% of all cases in children 2.  Most none-‐sporadic cases in adults

–  Atypical form •  Exhibit autosomal dominant or recessive inheritance •  Associated with deficiencies in proteins that regulate the alterna7ve pathway of complement ac7va7on

•  Adult-‐onset HUS –  Primary—no iden7fiable cause –  Secondary—associated with

•  Bacterial infec7ons—classic HUS •  ConnecCve Cssue diseases—SLE, Marfan syndrome, Ehlers-‐Danlos syndrome •  Cancer à stomach, colon, breast

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Diagnosis

•  Diarrhea (ozen bloody) •  Hematological

•  Microangiopathic haemoly7c anemia •  Thrombocytopenia

Fragmented red cells

Absence of platelets

ACUTE KIDNEY INJURY

Mechanism of Ac7on in Typical HUS •  Subdivided into 2 groups

1.  Bloody diarrheal prodrome (+) 2.  Bloody diarrheal prodrome (-‐)

Ø  Diarrhea-‐related (classic)—(D+)HUS 1.  E. coli O157:H7

•  Found in GI tract of cable •  Majority of human infec7ons traced to inges7on of incompletely cooked beef contaminated with the organism

•  Associated with verocytotoxin (shiga-‐like toxin I and II) produced during E. coli infec7on

2.  S. dysenteriae serotype I •  Produces Shiga toxin

Ø  Non-‐diarrhea-‐associated—(D—)-‐HUS

–  Reported in both children and adults –  Sporadic disease NOT preceded by diarrhea –  Endemic HUS

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80-‐90%

cases

10% cases

Proposed Mechanism Platelet-‐Fibrin Forma7on in “Classic” HUS

1.  Shiga toxin binds to Gb3 receptor on EC’s –  Local damage to colon mucosa

2.  Shiga toxin enters circula.on –  Damages EC’s of capillaries in

glomeruli – may impair ADAMTS13 on these EC’s)

3.  Causes release of ULvWF à platelet ac7va7on à microthrombi forma7on à renal failure

4.  TF released à ac7va7on of coagula7on cascade à fibrin forma7on

5.  Erythrocytes damaged as trapped in thrombi à Schistocytes + intravascular hemolysis à splenic sequestra.on

6.  Shiga toxin damages the endothelial cell causing the release of ULvWF

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UPSHAW-‐SHULMAN SYNDROME

•  Congenital deficiency of ADAMTS-‐13 1.  Protease cleaves vWF mul7mers 2.  Presents at birth with hemoly7c anemia and thrombocytopenia 3.  Renal involvement develops later in life

•  Inhibitor auto-‐an7bodies to ADAMTS-‐13 can also cause similar syndrome

Brass, L, 2001, Nature Med 7:1177-1178.

TTP versus HUS

TTP HUS

•  Adults—20-‐50 •  Children <5 years old

Pentad Tetrad

•  Hemoly7c anemia with RBC fragmenta7on •  Hemoly7c anemia with RBC fragmenta7on

•  Renal dysfunc7on •  Acute renal failure

•  Thrombocytopenia (35,000) •  Thrombocytopenia (95,000)

•  Severe CNS symptoms •  Mild CNS symptoms

•  Fever

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Disorders of the Vascular System

•  Structural abnormality or damage either to the endothelial lining or the subendothelial structures à variety of clinical manifesta7ons

•  Disorders classified –  Inherited disorders caused by

•  Abnormal synthesis of subendothelial connec7ve 7ssue components

–  Acquired disorders caused by an underlying disease of condi7on •  Decreases the suppor7ve connec7ve 7ssue in the blood vessel wall •  Abnormal proteins in the vascular 7ssue •  Infec7ons or allergic condi7ons •  Mechanical stress

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Hereditary Vascular Disorders •  Hereditary Hemorrhagic Telangiectasia (HTT)

–  Gene7c disorder that causes abnormali7es of blood vessels –  Blood vessels that lack capillaries between an artery and vein –  Under high pressure blood flows through arteriovenous malforma7ons –  These are fragile sites that are easily ruptured and result in bleeding –  Can occur in the skin or any organ

•  Ehlers-‐Danlos Syndromes (Oslo-‐Weber-‐Rendu Syndrome) –  Heterogeneous group of inherited connecCve-‐Cssue disorders characterized

1.  Joint hypermobility 2.  Cutaneous fragility 3.  Hyperextensibility

–  Associated with arterial rupture and visceral perforaCon, with possible life-‐threatening consequences

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Marfan Syndrome •  Marfan syndrome is an autosomal dominant

gene7c disorder of the connecCve Cssue •  1 in 5,000 people in the United States have

the disorder •  Unusually long limbs, great stature, or long

toes (or fingers) in propor7on to the person's height

•  PredisposiCon to cardiovascular disease •  Muta7on in the fibrillin-‐1 gene (FBN1)—

chromosome 15 •  Fibrillin—major building block of microfibrils

–  Serves as substrate for elas7n in the aorta and other connecCve Cssues

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Acquired Disorders of the Vascular System •  Acquired disorders caused by an underlying disease of condi7on

–  Decreases the supporCve connecCve Cssue in the blood vessel wall •  Senile purpura

–  Ecchymoses that appear with unrecognized or minor trauma in elderly individuals –  Extracellular matrix components of the skin degenerate à loss of suppor7ve collagen

fibrils à capillaries burst with minor pressure •  Cushing syndrome and corCcosteroid therapy

–  Excess endogenous glucocorCcosteroids (Cushing syndrome) à breakdown in collagen –  Exogenous (therapeu7c) glucocorCcosteroids à breakdown in collagen

•  Scurvy –  Deficiency of vitamin C which is needed for collagen synthesis à abnormal collagen

producd7on à vascular fragility and bleeding

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Acquired Disorders of the Vascular System

•  Abnormal proteins in the vascular Cssue –  Paraproteins

•  Monoclonal immunoglobulins produced by monoclonal neoplas7c plasma cells

•  Paraproteins bind to calcium à interference with coagula7on and deposi7on of light chain proteins in the vascular wall

–  Amyloidoisis •  Deposits of amyloid (misfolded or modified protein) form in the skin, perivascular 7ssue, and vessel walls à leads to fragility of the vessels and bruising

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Acquired Disorders of the Vascular System •  Henoch-‐Schönlein purpura

•  Small-‐vessel vasculiCs characterized by IgA, C3, and immune complex deposi7on in arterioles, capillaries, and venules

•  HSP affects mostly children and involves the skin and connec7ve 7ssues, gastrointes7nal tract, joints, and scrotum as well as the kidneys

•  Drugs –  Drugs from almost every pharmacologic class have been implicated in causing vasculi7s in

sporadic cases

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Acquired Disorders of the Vascular System •  Miscellaneous causes

–  Mechanical purpura •  Increased pressure within the lumen of the capillaries azer intense exercise, coughing

spasms –  Purpura fulminans

•  Associated with abnormali7es of certain clo�ng factors or their inhibitors •  Thrombi form in small vessels supplying the skin and subcutaneous 7ssue à necrosis

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Lab Tests in Disorders of Primary Hemostasis

Platelet count

PT APTT Bleeding Cme

Vascular disorder Normal Normal Normal Normal or abnormal

Thrombocytopenia Decreased Normal Normal Abnormal

Platelet Dysfunc7on Usually Normal

Normal Normal Normal or Abnormal

Most vascular diseases 1.  Are not associated with platelet or plasma defects 2.  Most common symptom

•  Abnormal bleeding into or under the skin due to increased permeability to blood

3.  Laboratory tests are used to exclude •  Coagula7on or platelet disorders

4.  Majority of pa7ents •  Hemosta7c tes7ng is en7rely normal, despite a history or physical

examina7on that suggests substan7al bleeding

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Science

Lecture 4, fall 2014 pdf