An Update on the Pathogenesis and Treatment of TTP

1
An Update on the Pathogenesis and Treatment of TTP

• Morey A. Blinder, MD
• Associate Professor of Medicine and Pathology
• Washington University
• St. Louis, MO

2
Classification of Platelet Disorders

• Quantitative Disorders
• Abnormal distribution
• Dilution effect
• Decreased production
• Increased destruction

• Qualitative Disorders
• Inherited disorders (rare)
• Acquired disorders
• Medications
• Chronic renal failure
• Cardiopulmonary bypass

3
Acquired thrombocytopenia with shortened
platelet survival

• Associated with bleeding
• Immune-mediated thrombocytopenia (ITP)
• Most drug-induced thrombocytopenias
• Most others

• Associated with
• thrombosis
• Thrombotic thrombocytopenic purpura
• DIC
• Trousseaus syndrome
• Heparin-associated thrombocytopenia

4
Eli Moschcowitz (1879-1964) In hospitals,
people should be treated and not diseases.

• Emigrated from Hungary to America at age 2
• Qualified in Medicine at Mount Sinai Hospital
  1903
• Studied Pathology with Ludwig Pick in Berlin
• Brother Alexis Victor was clinical professor of
  Surgery
• Many contributions to medical knowledge

5
Thrombotic thrombocytopenic purpura
An 18 year old girl presented with abrupt onset
of fever, anemia, renal dysfunction, CNS
impairment and cardiac failure. She died 2
weeks later.
Moschcowitz, E. Arch Int Med 1925 3689-93.
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Thrombotic thrombocytopenic purpuraDemographics

• Incidence 1100,000 - 1500,000
• Malefemale 12
• Age
• Most common in 30-40 year olds
• 90 of patients 60 years old
• No racial differences
• No seasonal difference

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Thrombotic Thrombocytopenic Purpura

• Clinical findings
• Fever
• Neurologic changes
• Renal impairment
• Laboratory findings
• Microangiopathic hemolytic anemia
• Thrombocytopenia

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Laboratory Findings in TTP

• Thrombocytopenia lt 20,000/µl
• Anemia lt 10g/dl
• Reticulocytosis
• LDH
• Indirect bilirbuin
• Haptoglobin

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Schistocytes Microangiopathic hemolytic anemia
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Defining the diagnosis of TTP

• Anemia may not be apparent at diagnosis
• Alternative diagnoses may only be apparent after
  treatment has begun
• The initial diagnosis should be considered
  tentative
• Remain vigilant for an alternative diagnosis

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Alternative diagnoses of patients who have
clinically suspected TTP/HUS

• Apparent after the plasma exchange has begun
• Autoimmune disorders
• Systemic lupus erythematosus
• Scleroderma
• Anti-phospholipid antibody syndrome
• Sepsis
• Malignant hypertension
• Heparin-induced thrombocytopenia/thrombosis
• Disseminated malignancy

12
Presentations of TTP/HUSThrombotic
microangiopathy

• Idiopathic
• No apparent etiology or associated condition
• Drug-induced
• Allergic Quinine, ticlopidine
• Dose-related Mitomycin, gemcitabine, cyclosporin
• Pregnancy/postpartum
• Diarrhea-associated
• Bone marrow transplantation
• Congenital

13
Changing incidence and clinical spectrum of
TTP-HUS

• Methods
• 168 consecutive patients over 10 years (U
  Oklahoma)
• BMT patients excluded
• Results
• Incidence 4.9/million/year -gt 9.5/million/year
• Associated findings Alternative diagnosis 49
  (29)
• Idiopathic 70 (42) Autoimmune disease 23
• Drug-induced 19 (11) Sepsis 10
• Pregnancy 18 (11) Malignancy 6
• Bloody diarrhea 12 (7) HIT 4
• Malignant HTN 3
• 
  HIV 2
• 
  MOF 1

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Changing incidence and clinicalspectrum of
TTP-HUS

• Conclusions
• The diagnosis of TTP-HUS is increasing
• This may be related to over-diagnosis
• This may be related to more drug-induced cases

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Thrombotic Thrombocytopenic PurpuraA Disorder of
VWF Proteolysis?
Increasing incidence? Often strikes young adults,
mainly females
Untreated, mortality gt90 Treated with
plasmapheresis, mortality lt20
16
ADAMTS13, VWF, and TTP

• Structure and function of ADAMTS13
• Mutations in congenital TTP
• Pathophysiology of microangiopathy
• Treatment of TTP

17
The Von Willebrand Factor Precursor
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Weibel-Palade Bodies
0.5 mm
Courtesy of Elizabeth Cramer
19
von Willebrand Factor Multimers
120 nm
Adapted from Fowler et al, J Clin Invest
761491-1500, 1985
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VWF Multimers in TTP
Endothelial Cell
Normal Plasma
Active
Remission
Unusually large Multimers
Moake et al, NEJM 3071432, 1982
21
VWF and Platelet Adhesion
22
Shear and VWF Proteolysis

• Proteolysis increased by
• Shear stress, denaturants
• VWD type 2A mutations

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VWF, ADAMTS13, and TTPFeedback Regulation of
Platelet Adhesion

• VWF Multimer Assembly
• Conserved mechanism
• Prevents multimerization in the ER
• Enables disulfides to form in the Golgi

• Proteolysis by ADAMTS13
• Cleaves VWF Tyr1605-Met1606
• Increase causes VWD (type 2A)
• Decrease causes TTP

Control of VWF multimer size is essential
24
VWF, Proteolysis, and Platelet Adhesion
25
Von Willebrand Disease Type 2A

• Clinical Features
• Autosomal dominant (occasionally recessive)
• Variable severity
• Prevalence - similar to type 2B, 2N
• Laboratory Features
• Factor VIII
• VWF Antigen
• Ristocetin Cofactor
• Multimers Plasma - no HMW
• Platelets - variable

Decreased or Normal
Markedly decreased
26
Plasma VWF Multimers
N
1
2B
3
2A
27
VWF Assembly and Catabolism

• Normal steady-state
• Normal multimer distribution
• Normal hemostasis
• Decreased assembly OR Increased catabolism
• Decreased large VWF multimers
• Bleeding (e.g., von Willebrand disease)
• Increased assembly OR Decreased catabolism
• Unusually large VWF multimers
• Thrombosis (e.g., Thrombotic thrombocytopenic
  purpura)

28
VWF Cleaving Protease in Plasma

• Discovered in 1996 by Tsai and by Furlan
• Requires Ca2 and Zn2 ions
• Cleaves VWF between Tyr1605 - Met1606
• Activated by shear stress, mild denaturants

• Absent in children with congenital TTP

• Absent in most adults with idiopathic TTP
• (acquired IgG autoantibody inhibitor)

29
Purified VWFCP
1
10
20 AAGGIL(H)LE(L)L(
D)AXG(P)X(V)XQ---
Fujikawa et al, Blood 2001 981662-1661
30
VWF Cleaving Protease(ADAMTS13)
Chromosome 9q34
Zheng and Chung et al, J Biol Chem 2001
27641059-41063
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VWF Cleaving Protease(ADAMTS13)
Metalloprotease
Thrombospondin 1
Disintegrin
A Disintegrin-like And Metalloprotease with
ThromboSpondin-1 repeats
32
VWF Cleaving Protease(ADAMTS13)
Ligand binding?
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Mechanisms of Thrombotic Microangiopathy
ADAMTS13-Dependent (TTP)

• Lesions rich in VWF and platelets, poor in fibrin
• Exacerbated by stress, endothelial injury
• Inherited ADAMTS13 deficiency
• Responds to plasma infusion
• Autoimmune ADAMTS13 deficiency
• Idiopathic - majority
• Drug-associated - ticlopidine, clopidogrel
• Responds to plasma exchange
• May benefit from immunosuppression

34
Mechanisms of Thrombotic Microangiopathy
Factor V Leiden-Dependent (TTP)
V Leiden V Leiden 0 16 4 7 Contro
ls 6 180
TTP and ADAMTS13 TTP and ADAMTS13
P lt 0.001, OR 17 (5.4 - 54)
Raife et al, Blood 2002 99 437-442
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Mechanisms of Thrombotic Microangiopathy
Complement Factor H Deficiency (HUS)

• Impaired inactivation of C3b, C4b
• Complement-mediated tissue injury
• Microvascular thrombosis
• Lesions rich in fibrin, poor in VWF and platelets
• Relatively severe renal damage
• Uncertain relationship to ADAMTS13 or VWF
• May respond to plasma infusion

36
Mechanisms of Thrombotic Microangiopathy
Verotoxin-induced (HUS)

• Lesions rich in fibrin, poor in VWF and platelets
• Relatively severe renal damage
• Epidemic bloody diarrhea (e.g., E. coli O157H7)
• Verotoxin is cytotoxic
• Binds globotriaosylceramide on endothelium
• Inhibits protein synthesis
• No demonstrated role for plasma therapy

37
Mechanisms of Thrombotic Microangiopathy
Many uncharacterized associations

• Bone marrow transplantation
• Pregnancy
• Non-immune drug toxicities

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Initial treatment of TTP

• Plasma exchange
• Replace 1-1.5 volume of plasma daily
• Adjunctive therapy
• Glucocorticoids
• Aspirin
• Dipyridamole

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Response to initial therapy

• Rapid response (1-2 days)
• Non-focal neurologic symptoms
• Moderate response (3-10 days)
• Thrombocytopenia
• Parameters of hemolysis (LDH)
• Slow response (weeks-months)
• Anemia
• Renal insufficiency (unpredictable and often
  incomplete)

Treatment requires persistence and patience
42
Complications of plasma exchange treatment
Approximate Complication frequency
() Central-venous catheter related
Procedure(Pneumothorax,Hemorrhage) 1-4
Infection 10-15 Thrombosis
(Catheter or venous)
10 Plasma-related Allergic (Urticaria,hypotens
ion, hypoxia) 4 Alkalosis Volume
depletion Transfusion-transmitted infection
lt1 Apheresis-machine related
Unintentional platelet pheresis ?
Rizvi, MA et al. Transfusion 2000 40896-91.
43
Follow-up and outcome

• Follow up
• Duration of initial treatment is undefined
• Monitor CBC and LDH
• Outcome
• Relapse rates 29-82
• Chronic renal insufficiency (25)
• Long term neurologic effects (incidence ?)

44
Approach to treatmentRelapse or refractory
patients

• Continue/intensify plasma exchange
• Aspirin/dipyridamole/glucocorticoids
• Splenectomy
• Immunosuppressive therapy
• Vincristine
• Other
• Intravenous immunoglobulin (IVIg)

45
TTP and ADAMTS13

• Plasma exchange does not address the underlying
  autoimmune disorder
• Refractory disease may benefit from
  immunosuppression
• ADAMTS13 and inhibitor assays may become useful
  to guide therapy

46
TTP and ADAMTS13 Response to Plasma Exchange
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Idiopathic TTP Group 1 Response to Plasma
Exchange

• 5 patients with
• Low protease
• No inhibitor
• Single episode

• Plasma exchange
• Good response
• Increased protease

Why protease deficient? Clearance antibody? Other
factors?
48
Idiopathic TTP Group 2 Response to Plasma
Exchange

• 5 patients with
• Low protease
• High inhibitor
• Multiple relapses

• Plasma exchange
• Good clinical response
• No change in protease
• Persistent inhibitor

Why is PE effective?
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Immunosuppressive Therapy in TTP
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Immunosuppressive Therapy in TTP
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Immunosuppressive Therapy in TTP
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Immunosuppressive Therapy in TTP
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TTP treatment and ADAMTS13

• Plasma exchange does not address the underlying
  autoimmune disorder
• Refractory disease may benefit from
  immunosuppression
• ADAMTS13 and inhibitor assays may become useful
  to guide therapy

54
Summary and goals for further research

• Diagnosis of TTP/HUS is often uncertain
• Etiology and pathogenesis
• Laboratory testing
• Plasma exchange is the most effective treatment
• Duration of therapy
• Role of adjunctive therapy is uncertain
• Treatment of relapse and refractory disease is
  undefined