Platelets -H/O Flashcards

1
Q

Mechanisms of Thrombocytopenia

A
  1. Decreased Production
    - Bone marrow failure (aplastic anemia, MDS, inherited marrow failure states)
    - Marrow replacement (leukemia, lymphoma, metabolic disorders)
    - Marrow toxins (drugs, radiation, ethanol)
    - Nutritional deficiency (B12, folic acid)
  2. Increased Destruction / Consumption
    - Immunologic (drugs, HIT, ITP)
    - Non Immunologic (DIC, TTP/HUS)
  3. Hypersplenism
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2
Q

Drug Induced Thrombocytopenia

A

-can directly affect the marrow
OR
-can have antibodies directed against drug/platelet complex or drug induced antibody response
Tx-stop offending drug

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3
Q

HIT

A
  • Immune response directed against heparin / platelet factor 4 complexes
  • Anti-Hep/PF4 IgG binds to platelet Fc receptors, resulting in platelet activation and generation of microparticles and thrombin
  • Thrombocytopenia begins 5 - 10 days after initiation of heparin exposure (may occur sooner in patients with recent exposure and residual antibodies)
  • More than 50% decrease from baseline platelet count or absolute thrombocytopenia
  • Absence of other causes of thrombocytopenia
  • ANY form of heparin can precipitate HIT (although less common with low MW heparins)
  • Confirmation by lab testing
  • Return to normal platelet count when heparin is discontinued
  • Venous and / or arterial thrombosis occurs in 30 - 50% - 10% require limb amputation, 20% mortality
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4
Q

Immune Thrombocytopenic Purpura (ITP)

A
  • Loss of tolerance to self
  • IGG antibody against glycoprotein IIb/IIIa, Ib/IX
  • Cytokines, abnormal T cells…
  • Autoantibodies that bind to platelets and accelerate their clearance by the spleen
  • ITP is a diagnosis of exclusion
  • Most common cause of thrombocytopenia in childhood, adolescence and young adults

Childhood ITP:
-Acute onset, often after viral illness
-Often resolves spontaneously within days or weeks
>90% resolve 1-2 years after dx

Adult ITP:

  • Insidious onset (most have symptoms for > 2 months)
  • Rarely resolves spontaneously
  • May patients go on to have chronic ITP
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5
Q

Clinical Features of ITP

A
  • Most adults have symptoms for > 2 months, children have symptoms for a day or two
  • Most children have no associated health issues
  • Most adults have other associated medical issues – autoimmune disorders, malignancy, etc.
  • Petechiae in dependent regions
  • Echymosis
  • Menorrhagia, epistaxis, gingival bleeding, blood in stool or urine
  • Otherwise healthy
  • No lymphadenopathy or splenomegaly
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6
Q

Laboratory Features of ITP

A
  • Severe thrombocytopenia (platelets < 10,000)
  • In adults or in patients with more insidious onset platelet count may be in range of 20-60,000.
  • CBC otherwise normal, MPV high
  • Peripheral smear may show large platelets
  • Normal coagulation times (PT/INR, PTT) and fibrinogen
  • Normal/increased megakaryocytes in bone marrow
  • Platelet antibody tests are rarely helpful
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7
Q

Treatment of ITP

A

ADULTS

  1. Steroids
  2. IVIG
  3. WinRho
  4. Rituxan
  5. Splenectomy
  6. Observation

Children

  1. Observation – 75%
  2. IVIG
  3. WinRho
  4. Steroids
  5. Rituxan
  6. Splenectomy
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8
Q

Disseminated Intravascular Coagulation

DIC

A
  • Life-threatening coagulation disorder caused by excessive activation of coagulation system that overwhelms natural anticoagulant mechanisms
  • Microvascular thrombi cause widespread tissue ischemia and multiple organ dysfunction
  • Bleeding due to consumption of platelets and plasma clotting factors
  • Thrombocytopenia
  • Prolonged coagulation times (PT/INR, PTT)
  • Low fibrinogen, other coagulation factors also low
  • Schistocytes on blood smear
  • VERY ILL appearing
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9
Q

Disseminated Intravascular Coagulation

(DIC) - causes/tx

A
Causes
-Infection / sepsis
-Malignancy
-Obstetrical catastrophes (abruption placenta, amniotic fluid embolism, retained tissue)
-Severe tissue injury (trauma, burns)
Tx
-Treat the underlying cause
-Transfuse platelets, FFP, cryoprecipitate as needed
-Consider low dose heparin
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10
Q

Classification of thrombotic thrombocytopenic purpura (TTP)

A
  1. Idiopathic
  2. Secondary
    - Pregnancy
    - Autoimmune disease (SLE, scleroderma)
    - Drug toxicity (chemotherapy, CSA, ticlopidine)
    - HIV infection
    - Bone marrow transplant
    - Malignancy
  3. Familial
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11
Q

Classic Pentad of TTP

A
  1. Thrombocytopenia
  2. Microangiopathic hemolytic anemia
  3. Neurologic symptoms
  4. Renal dysfunction
  5. Fever
    - If you wait for the entire pentad to develop, you have waited too long !
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12
Q

Diagnosis of TTP

A
  1. High index of clinical suspicion
  2. Hemolysis + Thrombocytopenia = TTP, DIC…
  3. Coagulation times should be normal, or only slightly prolonged
  4. Examination of the peripheral blood smear is absolutely essential !
  5. ADAMST 13 level
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13
Q

Treatment of TTP

A
  • Treatment must be started promptly
  • Plasma exchange has been the main treatment modality since the early 1980s
  • Prior to the use of plasma exchange, the mortality rate for TTP was 90%
  • With prompt diagnosis and treatment, 90% of patients now survive
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14
Q

Hemolytic uremic syndrome

A
  • Seen primarily in children
  • Predominantly renal symptoms, anemia and thrombocytopenia
  • Associated with infections with E coli or Shigella dysenteriae
  • Patients often require dialysis
  • Therapy is generally supportive
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15
Q

HIT summary

A
  • Heparin exposure
  • Platelets drop more than 50% from baseline
  • Variable INR, PTT, Fibrinogen
  • Life- and limb-threatening
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16
Q

ITP summary

A
  • Healthy
  • Severe thrombocytopenia, CBC otherwise normal
  • Normal INR, PTT, Fibrinogen
  • Rarely life-threatening
17
Q

DIC summary

A
  • Sick, bleeding > thrombosis
  • Falling platelets
  • Prolonged INR, PTT, low fibrinogen
  • Treat the underlying cause
18
Q

TTP / HUS

A
  • Sick, bleeding and thrombosis, CNS, renal
  • Falling platelets, MAHA
  • Normal INR, PTT, fibrinogen
  • 90% fatal if unrecognized and untreated