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PBR: Hematology > Platelet Disorders > Flashcards

Platelet Disorders Flashcards

1
Q

What is the normal lifespan of a platelet?

A

7-10 days

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2
Q

Name nine conditions associated with thrombocytopenia.

A

ITP, DIC, thrombotic thrombocytopenic purpura (TTP), hemolytic uremic syndrome (HUS), HELLP syndrome (Hemolytic anemia, Elevated Liver function tests, Low Platelets), dilution, transfusion, amniotic fluid embolism, and drug-induced thrombocytopenia.

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3
Q

Name (6) drugs that can cause thrombocytopenia.

A

Heparin, quinine, quinidine, phenytoin, gold salts, and alcohol.

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4
Q

What is the expected platelet morphology in patients with Bernard-Soulier syndrome?

A

Large platelets

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5
Q

What is the expected platelet morphology in patients with Wiskott-Aldrich syndrome?

A

Small platelets

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6
Q

What are the expected smear findings in patients with MYH9-related disorders?

A

Large platelets and white cell inclusions called Dohle bodies

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7
Q

What is the expected platelet morphology in patients with gray platelet syndrome?

A

Pale platelets

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8
Q

What is Wiskott-Aldrich syndrome?

A

An extremely rare X-linked disorder characterized by severe thrombocytopenia and small platelets that can develop in the neonatal period. Affected males develop eczema and immunodeficiency.

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9
Q

How might one differentiate between the thrombocytopenia of Wiskott-Aldrich syndrome and that of ITP?

A

Platelets are small in Wiskott-Aldrich, and large in ITP.

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10
Q

What oncologic process are patients with Wiskott-Aldrich at higher risk for developing?

A

Lymphoma

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11
Q

What are the expected clinical features of patients with Wiskott-Aldrich syndrome?

A

Severe thrombocytopenia with small platelets, eczema, and immunodeficiency.

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12
Q

What is the inheritance pattern associated with Wiskott-Aldrich syndrome?

A

X-linked

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13
Q

What are the clinical characteristics of patients with MYH9-related disorders?

A

Bleeding tendency, renal failure, sensorineural hearing loss, and/or cataracts.

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14
Q

What is TAR syndrome?

A

Amegakaryocytic Thrombocytopenia with Absent Radii. An inherited disorder that presents with bleeding in the neonatal period. Thrombocytopenia is severe, and there is an increased risk of death during the neonatal period and early infancy as a result of intracranial bleeds associated with platelet counts of <30,000.

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15
Q

When do most patients with TAR syndrome present?

A

Half are symptomatic within the first week of life, and 90% are symptomatic by 4 months of age.

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16
Q

How might one differentiate between patients with absent radii due to TAR syndrome vs those with absent radii due to Fanconi anemia or Trisomy 18?

A

Patients with TAR syndrome have absent radii but normal thumbs. Those with Fanconi anemia and Trisomy 18 have absent radii and abnormal thumbs.

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17
Q

What physical exam abnormalities can be seen in patients with TAR syndrome?

A

Absent radii, other upper extremity abnormalities (hypoplastic carpals and phalanges, syndactyly, clinodactyly, and phocomelia), lower extremity abnormalities (hip dysplasia, femoral and/or tibial torsion, and deformities of the knees and/or feet), dysmorphic facial features (micrognathia, hypertelorism, broad forehead, low-set and posteriorly rotated ears), and congenital heart disease (most often ASD, VSD, or tetralogy of Fallot).

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18
Q

How is clinically significant bleeding treated in patients with TAR syndrome?

A

With platelet transfusion.

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19
Q

What are the three potential processes for the development of acquired thrombocytopenia?

A

Decreased production of platelets, increased destruction of platelets, and sequestration of platelets in an enlarged spleen.

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20
Q

What should you suspect if a patient with sepsis has associated thrombocytopenia?

A

DIC

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21
Q

What blood disorder is common in neonates with CMV?

A

Thrombocytopenia

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22
Q

What is pseudothrombocytopenia?

A

It is not true thrombocytopenia. Platelets clump together in the collection tube, resulting in a factitiously low platelet count on the automated reader.

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23
Q

What is the next diagnostic step if a patient has an unexpectedly very low platelet count after previously having normal counts?

A

Review the smear to look for pseudothrombocytopenia. If present, redraw the sample in a sodium citrate tube to prevent clumping and thus provide an accurate count.

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24
Q

What preceding medical history is commonly reported in children diagnosed with ITP?

A

A history of recent (in the preceding 1-6 weeks) viral infection or immunization is found in a large percentage of those affected.

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25
Q

What is usually the first clinical sign of ITP?

A

Acute bruising, petechiae, or bleeding.

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26
Q

Within what age range does the peak incidence of ITP occur in children?

A

Between 2 and 5 years of age.

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27
Q

In what population is chronic ITP more common?

A

Chronic ITP more commonly occurs in adolescents and adults.

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28
Q

What is the incidence of intracranial hemorrhage in patients with ITP?

A

Intracranial hemorrhage occurs in <1% of children with ITP and is fatal in 1/3 of these cases.

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29
Q

Describe the peripheral blood smear findings in ITP.

A

The few platelets seen on the smear are megathrombocytes - large, but not as large as RBCs.

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30
Q

What diagnosis should be considered in a child with giant platelets (the size of RBCs)?

A

An inherited platelet disorder such as Bernard-Soulier syndrome.

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31
Q

What are the typical blood counts in children with acute ITP?

A

Unless significant bleeding has occurred, hemoglobin is usually normal. WBC count is also typically normal.

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32
Q

What laboratory finding can help to differentiate between ITP and TTP, HUS, or DIC?

A

ITP typically has thrombocytopenia with normal RBC and WBC counts. TTP, HUS, and DIC have thrombocytopenia as well as anemia.

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33
Q

What is the underlying mechanism for the development of thrombocytopenia in patients with ITP?

A

ITP is the result of immune-mediated platelet destruction.

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34
Q

What is Evans syndrome?

A

Evans syndrome is when ITP is found in association with autoimmune hemolytic anemia. Some patients also have autoimmune neutropenia. In this syndrome, autoantibodies are directed at specific, distinctly different antigens on each of the affected cell lines.

35
Q

What is the role of bone marrow aspiration and biopsy in the evaluation of a child with thrombocytopenia?

A

If the features aren’t classic for ITP or the platelet count does not increase with initial therapy, then bone marrow analysis is necessary.

36
Q

What bone marrow findings are consistent with a diagnosis of ITP?

A

Normal or increased numbers of megakaryocytes (the bone marrow is trying its best to increase production to make up for the autoimmune platelet destruction).

37
Q

How soon do platelet counts normalize in children with ITP?

A

Platelet counts normalize in nearly 80% of children with ITP within 12 months of diagnosis.

38
Q

What are some risk factors for the development of chronic ITP?

A

> 10 years of age, female gender, and insidious onset of initial symptoms.

39
Q

What are the laboratory and clinical indications for treatment of ITP?

A

Significant skin or mucosal bleeding, or platelet counts <10,000-20,000 even in the absence of significant bleeding.

40
Q

What is the typical platelet count trigger for treatment of ITP?

A

<10,000-20,000

41
Q

What medications should be avoided in patients with ITP?

A

NSAIDs, aspirin, and antihistamines

42
Q

What is the 1st line treatment for ITP?

A

IVIG is the first-line treatment, because it blocks the Fc receptors of the reticuloendothelial phagocytes and prevents them from binding and destroying the IgG antibody-coated platelets.

43
Q

What are two less-commonly used therapies for treatment of ITP?

A

Corticosteroids and Anti-Rh(D) immunoglobulin

44
Q

Why are platelet transfusions not generally used in the treatment of ITP?

A

They are not useful because they are destroyed by the same antibodies as the native platelets.

45
Q

What is the one clinical scenario in which platelets are used in the treatment of ITP? What other treatments are utilized concurrently?

A

If a patient with ITP has intracranial bleeding, platelets are given with IVIG, high-dose IV steroids, and, rarely, splenectomy.

46
Q

What is thrombotic thrombocytopenic purpura (TTP)?

A

A thrombotic microangiopathic hemolytic anemia typically caused by antibodies against ADAMTS13 (a protease that breaks down ultra-large von Willebrand factor multimers). The condition is life-threatening because of the risk of thrombosis in small arteries supplying the heart and CNS.

47
Q

What is the treatment for patients diagnosed with thrombotic thrombocytopenic purpura (TTP)?

A

Emergent plasmapheresis and corticosteroids.

48
Q

What are the characteristic laboratory findings in patients with thrombotic thrombocytopenic purpura (TTP)?

A

Anemia, thrombocytopenia, elevated LDH, hyperbilirubinemia, and azotemia.

49
Q

Describe the pathogenesis of maternal autoimmune neonatal thrombocytopenia.

A

If the mother has ITP during pregnancy, there is transplacental passage of IgG antibodies which also attack the neonatal platelets and result in neonatal thrombocytopenia.

50
Q

How long after birth does Maternal Autoimmune Neonatal Thrombocytopenia usually last?

A

1-2 months, then it resolves spontaneously as the maternal antibodies leave the infant’s system.

51
Q

Describe the clinical presentation and management of infants born to women with ITP.

A

IVIG is given during the 3rd trimester to mothers who have ITP, especially if there is maternal bleeding. In infants, IVIG is given for platelet counts <20,000. If the infant develops intracranial hemorrhage, give IVIG, steroids, and platelet transfusions.

52
Q

What is the Kassabach-Merritt phenomenon?

A

It is a condition characterized by destruction of platelets within certain vascular tumors of the skin, liver, or spleen.

53
Q

What tumors are associated with Kassabach-Merritt syndrome?

A

Tufted angiomas and kaposiform hemangioendotheliomas.

54
Q

What are some laboratory abnormalities associated with Kassabach-Merritt syndrome?

A

They can have evidence of a consumptive coagulopathy, with low fibrinogen, elevated D-dimer, anemia, and thrombocytopenia.

55
Q

What is the management for Kassabach-Merritt syndrome?

A

Medications (steroids, vincristine, propranolol, and interferon-α) and supportive care. The tumors often can’t be surgically excised or embolized if they are too large or inaccessible.

56
Q

Name three disorders of platelet function which are inherited.

A

von Willebrand disease, Bernard-Soulier syndrome, and Glanzmann thrombasthenia.

57
Q

What is the normal function of von Willebrand factor?

A

von Willebrand factor helps platelets stick to exposed subendothelium and other platelets. It is also the carrier protein for Factor 8.

58
Q

What is the prevalence and inheritance pattern of von Willebrand disease?

A

It is an autosomal dominant condition which affects up to 1% of the population.

59
Q

What are the clinical features of vWD?

A

Expression is variable - patients can have mild symptoms (bleeding with dental extractions and lifelong easy bruising) to more severe symptoms (frequent recurrent bleeding: nasal, oral, GI, and GU, including recurrent menorrhagia).

60
Q

What are the typical laboratory findings in patients with vWD?

A

PT is always normal. PTT is usually normal but can be prolonged in severe subtypes (due to decreased Factor 8). Bleeding time and platelet function analysis testing times are typically prolonged.

61
Q

What is often the first manifestation of von Willebrand disease in females?

A

Heavy menstrual bleeding

62
Q

Which form of von Willebrand disease is most common and what is the underlying defect?

A

Type 1 vWD is the most common subtype (90%) and is due to a decrease in the amount of vWF (i.e. it is a quantitative problem).

63
Q

What is the pathogenesis of Type 2 von Willebrand disease?

A

Type 2 von Willebrand disease has four different subtypes (2A, 2B, 2M, and 2N), but all are caused by qualitative defects in von Willebrand factor.

64
Q

Describe the clinical presentation and laboratory findings in patients with Type 3 von Willebrand disease.

A

Type 3 vWD is rare and presents with bleeding symptoms similar to those seen in patients with severe hemophilia. Patients have undetectable vWF levels and low Factor 8 levels.

65
Q

How does desmopressin (DDAVP) affect vWF and Factor 8 levels?

A

DDAVP causes a release of stored vWF and Factor 8 from endothelial cells.

66
Q

Which subtypes of von Willebrand disease may be treated with desmopressin (DDAVP)?

A

Because DDAVP causes a release of stored vWF and Factor 8 from endothelial cells, it can be used to treat and prevent bleeding in most patients with Type 1 vWD (quantitative defect) and some patients with Type 2A vWD (decreased binding of vWF to platelets).

67
Q

What are the treatment options for children with vWD?

A

DDAVP can be used to treat most patients with T1vWD and some patients with T2AvWD. In patients with these types of vWD who do not respond to DDAVP or who have major bleeding or surgery, vWF/Factor 8 concentrates may be used as well. Treatment with vWF/Factor 8 concentrates is required for patients with Type 2B, Type 2N, and Type 3 vWD.

68
Q

Why are vWF/Factor 8 concentrates preferred over cryoprecipitate in the treatment of von Willebrand disease?

A

The concentrates have a lower risk of viral contamination than cryoprecipitate.

69
Q

Giant, abnormal platelets and decreased platelet aggregation in response to ristocetin are seen in which inherited platelet disorder?

A

Bernard-Soulier syndrome

70
Q

What is the mode of inheritance for Bernard-Soulier syndrome?

A

Autosomal recessive

71
Q

What is the typical clinical presentation of patients with Bernard-Soulier syndrome?

A

These patients typically present with severe mucocutaneous bleeding in infancy.

72
Q

What is the underlying defect associated with Bernard-Soulier syndrome?

A

Bernard-Soulier syndrome is due to a deficiency of platelet glycoprotein 1b (GP1b) in the platelet membrane, which results in the inability of the platelets to aggregate properly.

73
Q

What laboratory abnormalities are expected in patients with Bernard-Soulier syndrome?

A

These patients have a prolonged bleeding time and platelet function analysis in conjunction with a mild thrombocytopenia and giant abnormal platelets on blood smear.

74
Q

What is the typical clinical presentation of patients with Glanzmann thrombasthenia?

A

These patients typically present with severe mucocutaneous bleeding in infancy.

75
Q

What is the mode of inheritance for Glanzmann thrombasthenia?

A

Autosomal recessive

76
Q

What is the cause of the dysfunction in Glanzmann thrombasthenia?

A

There is an abnormality in the gene encoding the fibrinogen receptor on platelets which leads to an inability of platelets to bind fibrinogen and aggregate.

77
Q

What does aspirin do to platelets? How long does it last?

A

Aspirin irreversibly inactivates platelet cyclooxygenase and alters platelet function for the entire lifespan of the platelet.

78
Q

Compare/contrast the effects of aspirin and NSAIDs on platelet function.

A

Aspirin irreversibly inhibits platelet function for the lifespan of the platelet, while NSAIDs reversibly inhibit platelet function.

79
Q

What is the major cause of bleeding in patients with renal disease?

A

These patients have platelet dysfunction that results from impaired platelet adhesiveness and decreased platelet aggregation.

80
Q

What is the definition of thrombocytosis?

A

> 500,000 platelets

81
Q

What is usually the cause of thrombocytosis in children?

A

Platelets are an acute phase reactant, and most thrombocytosis in children is due to some secondary cause: acute or chronic infection, iron deficiency anemia, inflammatory disorders, or acute blood loss.

82
Q

What treatment does reactive thrombocytosis require?

A

It is a benign condition that does not require specific therapy.

83
Q

What is essential thrombocytopenia?

A

A rare myeloproliferative disorder with persistent platelet counts >1,000,000. Thrombosis and bleeding commonly occur because platelet function is abnormal.

84
Q

How is essential thrombocytopenia usually treated?

A

In patients who are not bleeding, a platelet aggregation inhibitor such as aspirin is used. In addition, platelet lowering drugs such as hydroxyurea or anagrelide are prescribed.

PBR: Hematology (9 decks)

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