Lecture 8: Platelet Disorders Flashcards
ITP may be part of a broader disease affecting immune regulation such as what?
- HIV infection
- SLE
- Lymphoproliferative malignancy, especially in older pt’s
All pt’s with ITP should be screened for what infection; recent research has also linked ITP to what other infective agent?
- All pt’s should be screened for HIV
- Recent reports have linked ITP to H. pylori infection
What will blood smear of someone with ITP show?
Decreased platelets and occasional large platelets (megathrombocytes)
ITP can be triggered by almost any drug, but is most commonly seen in association with what?
Quinine or Quinidine
What are 2 effective therapies for ITP with severe thrombocytopenia or active bleeding is present?
Glucocorticoids and IVIG
Which 2nd line immunosuppressive agent will lead to doubling of the platelet count in 40% of pt’s with ITP?
Rituximab
Is splenectomy indicated for ITP?
Rarely, only in those w/ significant bleeding unresponsive to immunosuppressive medications
What should a CBC of pt with ITP show in terms of platelets, Hgb, Hct, and leukocytes?
- Low platelet count
- Normal Hgb, Hct, and leukocyte count
Although pt’s with heparin induced thrombocytopnia do not bleed excessively they have a dramatic risk what complications?
- DVT’sandPE’s
- Unusual clotting problems i.e., portal vein thrombosis or acute arterial occlusion
Which type of heparin is more likely to lead to HIT and which is less likely?
- Unfractionated heparin = more likely
- Incidence is 2-3x lower in pt’s receiving LMW heparin
What is the “4T Score” used clinically to determine the likelihood of HIT?
- Degree of Thrombocytopenia
- Timing of platelet count fall
- Thrombosis or other sequelae
- Other causes for Thrombocytopenia present
Describe the degree of thrombocytopenia associated with 2, 1, or 0 points using the “4T Score” in assessing HIT risk?
- 2 points = platelet count >50% fall and nadir ≥20,000/uL
- 1 point = platelet count 30-50% fall or nadir 10,000-19,000/uL
- 0 points = platelet count <30% fall or nadir <10,000/uL
Describe the timing of platelet count fall associated with 2, 1, or 0 points using the “4T Score” in assessing HIT risk?
- 2 points: clear onset btw days 5 and 10 or platelet count decrease at ≤1 day if prior heparin exposure within last 30 days
- 1 point: onset after day 10 or timing unclear, or ≤ day 1 if heparin exposure within past 30-100 days
- 0 points: platelet count fall <4 days without recent exposure
Describe the thrombosis or other sequelae category associated with 2, 1, or 0 points using the “4T Score” in assessing HIT risk?
- 2 points: confirmed nw thrombosis, skin necrosis, or acute systemic rxn after IV unfractionated heparin bolus
- 1 point: progressive or recurrent thrombosis, nonnecrotizing (erythematous) skin lesions, or suspected thrombosis not proven
- 0 points: no thrombosis or sequelae
Which findings for the category “other causes of thrombosis” are associated with 2, 1, or 0 points using the “4T Score” in assessing HIT risk?
- 2 points = no other cause apparent
- 1 point = another cause is possible
- 0 points = definite other cause
How many points using the “4T Score” for risk of HIT is associated with low, intermediate, and high probability of HIT?
- Low = 0-3 points
- Intermediate = 4-5 points
- High = 6-8 points
In patients with HIT, heparin should be discontinued and what should be administered?
Direct thrombin inhibitors (i.e., Lepirudin or argatroban)
Which findings is the simplest way to differentiate TTP from HUS?
- TTP = MAHA + thrombocytopenia (<50,000) + fever + neurologic sx’s
- HUS = add renal failure to the above
How do the hereditary vs. acquired forms of TTP differ?
- Hereditary = mutation of ADAMTS13 gene
- Acquired = autoantibodies directed at ADAMTS13; linked to pregnancy, HIV-infection, chemotherapy and immunosuppressive agents
What is the treatment for TTP?
- As in DIC, treat the underlying cause
- Plasmapheresis - life saving in virtually 100% of cases
- Glucocorticoids also recommended
How should young patients with TTP-HUS with features suggesting enteric bacterial toxins as the etiology be treated?
Supportively
What is the pathologic lesion of TTP; what will be seen on peripheral smear?
- Pathologic lesion is hyaline microthrombi which occlude the capillaries of virtually every organ in the body
- Schistocytes seen on peripheral smear
What is the hallmark of essential thrombocythemia and how is the diagnosis made?
- Thrombocytosis that cannot be explained by clinical conditions known to cause a reactive elevation in platelet count
- Dx made by finding persistent platelet counts >600,000 u/L with no other condition present leadin to reactive thrombocytosis
What are some genetic findings which can be helpful in diagnosing essential thrombocythemia?
- 50% of pt’s will have JAK2 mutation
- Since thrombocytosis may be seen in CML and PRV, diagnosis further requires that the Philidelphia chromososme be negative and the pt does not have concomitant erythrocytosis
What are 3 criteria which would place a patient with essential thrombocythemia in a low-risk category; how should they be treated?
- Those aged <60 year, have no prior thromboembolic event and platelet counts <1,000,000/uLhaveexcellent prognosis
- Should be observed without treatment
Pt’s with essential thrombocythemia who are not in the low-risk category should be treated how?
Tx with hydroxyurea + low-dose aspirin
Which 2 drugs can be added to reduce platelet count in pt with ET if deemed necessary based on sx’s refractory to salicylates alone?
Pegylated IFN-α or Anagrelide
Reactive thrombocytosis is almost always due to what 4 etiologies?
- Iron deficiency
- Inflammation
- Cancer
- Infections
