Prapti Patel

Resident Lecture Series

2.4.15

PLATELET DISORDERS: ITP, TTP, HIT

IMMUNE THROMBOCYTOPENIC PURPURA

• Barnes-Jewish Hospital, 1950:

postulated that patients with ITP had a

“blood factor” that caused destruction

of platelets

• To test this hypothesis, Harrington

received a transfusion of 500 ml of

blood from a patient with ITP.[

• Within three hours, his platelets

dropped to dangerously low levels

• platelet count remained extremely

low for four days, finally returning

to normal levels by the fifth day

PATHOPHYSIOLOGY OF ITP: HARRINGTON-

HOLLINGSWORTH EXPERIMENT

PATHOPHYSIOLOGY OF ITP

• Platelets phagocytized Membrane GPIIb/IIIa or GPIb/IX digested into a peptide and

presented to macrophages CD4+ T cell is activated T cell secretes IL-6 activate

antibody producing B cells autoantibodies bind to platelets platelets are phagocytized

by splenic macrophages

• Antibodies can bind to megakaryocytes, thus decreasing overall platelet production

PATHOPHYSIOLOGY OF ITP: WHAT CAUSES IGG

PRODUCTION?

• Infections: anti-viral antibodies cross react with platelet glycoproteins

• CMV, EBV

• HIV: molecular mimicry of HIV proteins and GPIIb/IIIa

• Hep C: molecular mimicry between HCV core envelope protein 1 and GP IIb/IIIa

• Bacterial products (LPS) attach to platelet surface and increase phagocytosis

• Autoimmune disorders

• SLE, antiphospolipid syndrome, post-HSCT thrombocytopenia, sarcoidosis

• Lymphoproliferative disorders

• CLL

• Drug associated ITP

• Fludarabine

• Purpura

• NOT palpable and asymptomatic

• Mucosal bleeding

• Blood blisters

• Asymptomatic

ITP: A VARIABLE CLINICAL PRESENTATION

EPIDEMIOLOGY

• Observational study in Denmark from 1973 to 1995 and UK from 1990 to 2005

• Incidence 22-44 per million per year

• 70% are Women

• 70% are under age 40

• Typically chronic disease and asymptomatic, lasting for years

• Acute and symptomatic in children

• Death from bleeding is rare

• Death more likely related to immunosuppression

• Evaluate for systemic disease

• Coagulation studies

• DIC, TTP

• MAHA: heart valves

• Splenomegaly

• Splenic sequestration

• hematologic malignancy

• Other cytopenias

• Marrow failure: MDS

• Lypmhoproliferative or myeloproliferative disorders

• EDTA dependent platelet agglutination

• Pregnancy

• Drugs

• Heparin, quinine, sulfas,

antibiotics

• Viral infections

• HIV, EBV, rubella, CMV

• Autoimmune disorders

• SLE

• Congenital platelet disorder

DIAGNOSIS OF EXCLUSION

Must have isolated thrombocytopenia and no other signs of systemic disease

DIAGNOSIS BY PERIPHERAL BLOOD SMEAR

DIAGNOSIS BY PERIPHERAL BLOOD SMEAR

Schistocytes: TTP, DIC, HUS Clumping: EDTA

INDICATIONS TO TREAT

• Major bleeding is rare in ITP

• Mostly occurs at <10,000

• Goal of treatment:

• Reach a platelet count that will prevent bleeding

• Prevent toxicity of treatment itself

• When to treat

• Asymptomatic with moderate thrombocytopenia does not require treatment

• General cutoff: 30,000/µL

• Watch for worsening thrombocytopenia or new onset of symptoms

FIRST LINE TREATMENT: STEROIDS

• Prednisone 1 mg/kg/day

• 40-60% response rate with a response by 2 weeks

• Taper after initial response occurs, with most flares occurring during taper

• Goal oft therapy

• Keep plt’s at 50,000 or greater

• Minimize steroid induced side effects

• Give calcium and vitamin D

• Check DEXA scan

INTRAVENOUS IMMUNOGLOBULIN

• Quick, but temporary response

• Can be used in life threatening bleeding or preparing for splenectomy/surgery

• Helps to prevent platelet destruction after transfusion

• 2 forms

• IVIg: 1 g/kg for 1-2 days

• Anti-Rh(D) in Rh+ patients: 50-75 mcg/kg/day

• Mechansm is unknown

• Inhibit the autoantibody and cause steric hinderance so antibody can’t bind to platelets

• Inhibit the Fc receptor of the macrophages, decreaseinguptake of antibody coated platelets

• Clinical Data (Br J Haematol. 1999;107(4):716.)

• 1g/kg dose resulted in platelet count >80,000 in 28% of patients by day 2 and 67% by day 4 (N=35)

IVIG

FAILURE OF TREATMENT

• Failure to respond to high dose gluccocorticoids

• No response after 2 weeks of therapy

• Continued symptomtatic thrombocytopenia

• Failure to maintain response

• Case sereies of 208 patients with ITP:

• 39% complete response rate with prednisone

• Only 18% sustained complere response at 6 months

• Am J Med. 1995;98(5):436.

• Mechanism of action:

• Spleen is major site of platelet destruction

• Spleen is 25% of total lymphoid mass, which produced autoantibodies

• Response rates

• Usually occurs within 2 weeks of surgery

• Complete remission rate of 60-70%

• Durable remissions

• Partial remission rate of 15-20%

SPLENECTOMY FOR REFRACTORY ITP

• Prospective controlled phase II trial

(Blood. 2008;112(4):999.)

• 60 patients with ITP >6 months

and platelet count of <30,000

• Given rituximab 375 mg/m2 Q

week x 4

• 40% able to maintain a plt count of

>50,000 at one year

• 33% at two years

• No trial comparing rituximab to

splenectomy

RITUXIMAB FOR REFRACTORY ITP

THROMBOPOIETIN RECEPTOR AGONISTS FOR

REFRACTORY ITP

• 118 patients with plt<50,000 and failed

one prior therapy randomized to oral

eltrombopag vs placebo

• End point: plt count >50K by day 43

• Eltrombopag 75 mg: 81%, mean

platelet count 183,000

• Placebo: 11%, mean platelet counts

16,000

• Patients with ITP randomized (2:1) to romiplostim vs placebo

• ½ had a splenectomy

• Given SQ weekly therapy for 24 wks to maintain plt count b/w 50-200K

• Assessed durable plt response: Goal platelet count maintained for >6 weeks

• Splenectomized:38% vs 0% (p<0.0013)

• Nonsplenectomized: 56% vs 0% (p<0.0001)

THROMBOPOIETIN RECEPTOR AGONISTS VS

PLACEBO

Romiplostim: Lancet. 2008;371(9610):395. Eltrombopag: N EJM. 2007;357(22):2237.

THROMBOPOIETIN STIMULATING AGENTS

• FDA approved for ITP in adults with insufficient response to steroids, IVIG, or

splenectomy

• ASH 2011 guidelines: use in patients at risk for bleeding who have a contraindication to

splenectomy and have failed at least one other therapy other than steroids

• EMA: approved these agents for "splenectomized adults who are refractory to other

treatments."

• Expensive: one year of Romiplostim is >$55,000

• Long term effects not known

• Increase risk of clotting/bleeding?

• Increase bone marrow fibrosis?

EMERGENT TREATMENT OF ITP

• Platelet transfusion

• IVIG: 1g/kg for 1-2 days

• High dose IV steroids

• Methylprednisolone 1 gram or 30 mg/kg/day for 2-3 days

THROMBOTIC THROMBOCYTOPENIC

PURPURA

HISTORICAL PERSPECTIVE

• First described in 1924 by Eli Moshcowitz

• 16 year old girl that presented with fever, anemia leukocytosis, petechiae, hemiparesis

• Urine had albumin and granular casts

• Died 2 weeks later

• Autopsy showed hyaline thrombi in terminal arterioles, especially heart and kidney

• 1966: First clinical review

• 272 patients with TTP

• Classic pentad of: thrombocytopenia, hemolytic anemia, neurological symptoms, fever,

renal damage

• Mortality 90%

• No one was treated with plasma

HISTORICAL PERSPECTIVE OF TREATMENT

• Transfusion therapy not looked at until 1976

• 14 patients had whole blood transfusions

• 8/14 had clinical response

• Plasmapheresis

• Response if replacement fluid was plasma

• No response if replacement fluid was albumin

• Conclusion: There’s something in the plasma that can ameliorate TTP

PATHOGENESIS

• Link between TTP and vWF made in 1982

• Based on study of 4 patients

• Had much larger vWF multimers

• Proposed a defect in depolymerase activity that would normally cleave vWF

• Plasma exchange provides this missing depolymerase activity

• 1996: metalloprotease in plasma shown to cleave vWF multimers

• Children with congenital TTP had a deficiency in this metalloprotease and adults with

acquired TTP had an antibody to it

• Metalloprotease was purified, cloned, and named ADAMTS13

STRUCTURE OF VWF

IDIOPATHIC TTP

• Polyclonal IgG autoantibody to ADAMTS13

• Associated with 30% relapse after initial remission

• Incidence 3.8 million a year in the US

• Peak incidence of idiopathic TTP is ages 30-50

• African ancestry

• Obesity

• Genetic predisposition

CLINICAL PRESENTATION-THE PENTAD

• Must haves:

• Hemolytic anemia

• Thrombocytopenia

• Purpura or petechiae

• Rarely bleeding

• Maybes: present in 50%

• Fever

• Renal failure

• Neurologic findings

• Headache

• Visual disturbances

• Vertigo

• Personality changes

• Confusion/lethargyComa

• Siezures

• Focal sensory or motor deficits/aphasia

• PRES

• Thrombocytopenia

-50% of patients have platelets <20,000

• Evidence of hemolysis

• 33% of patients have Hgb <6

• Schistocytes : >5 per high powered field

• Elevated retic count

• Evidence of tissue ischemia

• Elevated LDH: median LDH is 1200

• Ruled out AIHA, DIC

LABORATORY PRESENTATION

ADAMTS13 activity level is NOT a criteria

ADAMTS13 TESTING AS A DIAGNOSTIC TOOL

• ADAMTS13 activity correlates with clinical presentation, but not clinical course

• Study of 48 patients with clinical diagnosis TTP-HUS

• 16 had severe ADAMTS 13 deficiency

• Clinical course was variable and no different than other 32 patients

• Assay techniques are not standardized

• Levels vary with pregnancy, age, cirrhosis, CKD, postoperative course, acute

inflammatory states, sepsis, acute hepatitis, VOD after HSCT

• Activity level <5% is consistent with TTP

• Only 5% needed to maintain homeostasis

SECONDARY THROMBOTIC

MICROANGIOPATHY (TMA)

• Infection and DIC

• Malignancy

• Postop

• Malignant Hypertension

• Bone Marrow Transplant Patients

• Allografts

• Total body irradiation

• GVHD

• Autoimmune disorders

• Lupus vasculitis (TMA)

• Antiphospholipid Sx (TMA)

• Evans Sx

• Pregnancy

• HELLP (TMA)

• Eclampsia (TMA)

Not associated with ADAMTS13

deficiency

Can be associated with ADAMTS13

deficiency

DRUGS AS A CAUSE OF TMA

• Quinine

• Chemotherapy

• Mitomycin C

• Bleomycin

• Gencitabine

• Cisplatin

• Immunosuppression

• Cyclosporine

• Tacrolimus

• Ticlopidine

• Clopidogrel

• Treat like TTP with plasma exchange

• No relapse reported after stopping drug

Associated without ADAMTS13 antibody Associated with ADAMTS13 antibody

TREATMENT

• Plasma infusion (FFP): giving back

ADAMTS13

• More effective in congenital TTP

• Temporizing measure in acquired

TTP

• Plasma exchange: giving ADAMTS13 and

removing antibody and large vWF

multimers

• Exchange of single plasma volume

• Larger volume exchanges may have

benefit

TREATMENT: CRYO-POOR PLASMA

• Results from removal of cryoprecipitate from plasma

• Depleted in factor VIII, vWF, factor XIII, fibrinogen

• Can be used in patients with volume issues

• Still has ADAMTS13

• RCT of 27 patients comparing CPP and FFP demonstrated equivalence

• Time to response: 5.5 vs 6.0 days

• Survival: 79% vs 77%

TREATMENT: PLASMA EXCHANGE

• Continue daily until following is met for 3 days:

• Platelet count >150K

• LDH normal

• Resolution of neurologic symptoms

• Resolution of renal disease may be slow and incomplete

• Then taper to QOD to twice a week

• Average time on daily exchange: 7-16 days

• Time on exchange (including taper) is variable

• 3 to 145 exchanges

TREATMENT: STEROIDS

• Rationale: need to eliminate antibody production

• Benefit not clearly demonstrated

• Common practice: 1 to 2 mg/kg/day during plasma exchange then taper

• Alternative: methylprednisolone 1 gram IV daily for 3 days or 125 mg IV BID for 4 days

• Or can be started if plasma exchange cannot be tapered

RESISTANT OR RELAPSING DISEASE

• 10-20% of patients will have transient, incomplete, or no response to exchange

• Can increase the frequency of exchange or:

• Steroids

• Rituximab

• Cyclosporine

• Cyclophosphamide

PLATELET TRANSFUSION IN TTP

• Can correlate with acute decompensation and worsening thrombosis

• Retrospective study: 89 pts received platelet transfusions in setting of TTP

• 8% had new neurological event or death

• Study from TTP registry in Oklahoma reviewed course of 54 patients

• No difference in neurological events or death

• Party line on platelet transfusions:

• Do not need to transfuse platelets for procedures

• Can transfuse platelets prior to emergency surgery after plasma exchange

HEPARIN INDUCED THROMBOCYTOPENIA

(HIT)

COAGULATION CASCADE AND MECHANISM OF

ACTION OF HEPARIN

PATHOPHYSIOLOGY OF HIT

• Heparin causes thrombocytopenia: results in HIT

• Type I: non-immune mediated

• Platelet count falls 2 days after starting heparin and resumes to normal despite

continued heparin use

• Due to increased platelet activation

• Type II: immune mediated

• Due to formation of antibodies against heparin-platelet factor 4 complex

TYPE I VS TYPE II

Type I Type II

Frequency 10-20% 1-3%

Timing of onset after starting

heparin

1-4 days 5-10 days

Nadir platelet count >100,000 >20,000

Antibody mediated No Yes

Thromboembolic sequelae None 30-80%

Hemorrhagic sequelae None Rare

Management observe Stop heparin and start non-

heparin anticoagulant to

prevent arterial thromboses

Brieger, DB, Mak, KH, Kohke-Marchant, K, et al. J Am

Coll Cardiol 1998; 31:1449.

• Heparin and platelet factor 4 forms a

highly immunogenic complex

• PF4 is a heparin neutralizing

protein contained in alpha

granules of platelets

• Heparin induces a conformational

change in PF4, inducing a new

epitope

• Induces an antibody reaction

• IgG, IgM, IgA is formed

TYPE II IMMUNE MEDIATED HIT

• Once PF4-heparing complex forms, it binds to platelet surface

• HIT ab (usually IgG) binds to the surface/complex

• Fc portion of the antibody activates adjacent platelets, leading

• 1. platelet activation and release of additional PF4 and procoagulantmicroparticles

• 2. aggregated platelets, leading to increased removal by RES

TYPE II IMMUNE MEDIATED HIT

EPIDEMIOLOGY AND RISK FACTORS

• Seen in ~5% of patients treated with heparin

• Risk factors for developing HIT (Blood. 2006;108(9):2937.)

• Unfractionated heparin vs LMWH (RR 5.3; 95% CI 2.8-9.9)

• Surgical patients vs medical patients (RR 3.2; 95% CI 2.0-5.4)

• Female patients (RR 2.4; 95% CI 1.4-4.1)

• Female surgical patients receiving UFH (RR 17; 95% CI 4.2-72)

• Platelets decreased 30-50% from baseline during first 72 hours of bypass surgery

• due in part to prolonged contact of platelets with the artificial surface of the extracorporeal circuit

• usually receive large amounts of unfractionated heparin

• incidence of HIT antibodies is as high as 25 to 70 percent by immunoassay and 4 to 20 percent by platelet activation assay.

• several other potential causes of thrombocytopenia are often present

CARDIAC SURGERY

CLINICAL PRESENTATION

• Fall in platelet count >50% of baseline within 5-10 days of initiating heparin

• It takes 5-10 days to produce IgG

• Earlier onset can be seen be seen in prior exposure (due to preformed antibodies)

• No other cause of thrombocytopenia

• Platelet counts usually <20,000, median platelet count 60,000

• Bleeding is unusual

• Venous and Arterial Thrombosis (platelet rich)

• Due to activated platelets

• Most common: PE, limb gangrene, cerebral sinus thrombosis, DVT

• Less common: MI, CVA, organ infarction

• Skin necrosis

• Adrenal hemorrhage

• 0-3: low probablity of HIT (0.9%)

• 4-5: intermediate probability (11.4%)

• 6-8: high probability (34%)

CLINICAL DIAGNOSIS: 4T SCORE

2 points 1 point 0 point

Thrombocytopenia >50% fall and nadir ≥20k

30-50% fall, or nadir 10-19k;

or >50% fall directly resulting

from surgery

<30% fall,

or nadir <10k

Timingb of Platelet Count Fall

Clear onset between days 5-

14;

or ≤1 day (prior heparin

exposure within 30 days)

Consistent with day 5-14 fall, but

not clear (e.g. missing plt

counts);

or onset after day 14;

or ≤1 day (prior heparin

exposure 30-100 days ago)

Platelet count fall ≤4 days

without recent exposure

Thrombosis or other sequelae

New thrombosis (confirmed);

skin necrosis; acute systemic

reaction after iv UFH bolus

Progressive or recurrent

thrombosis; non-necrotizing

(erythematous) skin lesions;

suspected thrombosis (not

proven)

None

Other causes of

thrombocytopeniaNone apparent Possible Definite

• Heparin-PF4 complexes are coated on plate

• Patient serum is added

• If heparin IgG antibody is present, will bind to complex

• Alkaline phosphatase-labeled anti-human globulin added to detect the

IgG causing agglutination

• The optical density (OD) is reported: OD values >0.40 are considered

positive and indicate the presence of heparin-induced antibodies.

• OD: measure of penetrance of light

• Sensitivity: 91-97%, negative test rules out HIT

• Specificity: 74-86%, (hemodialysis patients, cross reactivity of other

antibodies or non-IgG HIT Ab)

LABORATORY DIAGNOSIS: ELIZA TEST

LABORATORY DIAGNOSIS: SEROTONIN RELEASE

ASSAY

• Gold standard for HIT diagnosis

• Platelets from normal donor are radiolabeled with 14C serotonin

• Patient serum added with heparin

• If HIT ab is present bind to heparinactivate plateletsgranules are emptied

• Positive test: 14C serotonin is released

• Sensitivity: >95%

• Specificity: 97%

• Not available in all centers

TREATMENT

• First step: stop heparin and LMWH

• Start anticoagulation with direct thrombin inhibitors to treat existing thromboses and

prevent new ones

• Lepirudin/Bivalirudin: renally cleared

• Argatroban: hepatically cleared

• 2 mg/kg/hr CIVI

• 3 trials let to FDA approval

• Arch Intern Med. 2003;163(15):

1849

• Circulation. 2001;103(14):1838.

• Chest. 2006;129(6):1407.

• Reduction in thrombotic events

• 0.1 to 0.15 mg/kg/hour CIVI

• Prospective series of 82 patients: 89%

of patients has increase in platelet

counts (Circulation. 1999;99(1):73.)

• Retrospective series of 205 patinets:

less death, amputation, new

thromboses than historical control,

25% vs 52% (J Thromb Haemost.

2005;3(11):2428.)

TREATMENT

Lepirudin Argatroban

LONG TERM THERAPY

• Transition to long term therapy once platelets return to normal (>150,000) with direct

thrombin inhibitors

• Warfarin

• Both DTI and warfarin increase INR

• Goal INR is 2-3

• 5 days of overlapping therapy with warfarin and DTI before DTI is discontinued

• Avoid induction of hypercoagulable state by lowering of protein C levels

• No firm data on length of therapy

• 3 months if no thrombosis

• 6 months if thrombosis was present

THE END