Severe Thrombocytopenia: Three VA cases

1. Severe Thrombocytopenia:Three VA cases Sarah Walter, M.D.

2. Thrombocytopenia • Thrombocytopenia is defined as a platelet count of < 150,000/ μL • Due to: • Increased destruction • Sequestration • Decreased production

3. Thrombocytopenia • Systematic approach to evaluating patients: • History (associated illness, drugs, specific symptoms) • Physical exam (anomalies, hepatosplenomegaly, infection, tumor, lymphadenopathy, bleeding) • Careful interpretation of the complete blood count and examination of peripheral smear • If diagnosis not made, consider bone marrow examination with needle aspiration and biopsy

4. Case 1

5. Case 1 • 49 year old female who presented to the Dermatology clinic with a petechial rash on her legs. She denied vaginal or mucosal bleeding. • History of depression and PTSD treated with ziprasidone, trazadone, vanlafaxine, clonazepam. And she recently started carbamazepine 2 weeks prior.

6. Pre-drug lab values (2 weeks ago): WBC: 6.5 x 1000/μL (4.5 – 11.0) RBC: 3.9 M/μL (4.6 – 6.2) Plt: 272 x 1000/μL (150 – 400) Hgb: 12.2 g/dL (14.5 – 18.1) Hct: 35.2% (42 – 54) MCV: 90.4 fL (80 – 100) MCH: 31.3 pg (28 – 34) RDW: 12.7% (11.5 – 14.5) Laboratory data at time of visit: WBC: 4.6 x 1000/μL (4.5 – 11.0) RBC: 4.45 M/μL (4.6 – 6.2) Plt: 3.32 x 1000/μL (150 – 400) Hgb: 12.6 g/dL (14.5 – 18.1) Hct: 39.5% (42 – 54) MCV: 88.9 fL (80 – 100) MCH: 28.4 pg (28 – 34) RDW: 12.8% (11.5 – 14.5) Case 1

7. Case 1 • Additional pertinent laboratory data: • PT: 11.9 sec (10.8 – 13.7) • aPTT: 19.9 sec (21.6 – 34.2) • Occult blood: Positive • UA: Negative for blood • Fe: 93 μg/dL (35 – 145) • TIBC: 314 μg/dL (275 – 400) • Ferritin: 133 ng/mL (25 – 180)

8. Case 1 • Smear:

9. Case 1 • Differential diagnosis: • Drug-induced thrombocytopenia • ITP • Infectious (viral) • TTP • DIC

10. Case 1 • Carbamazepine was discontinued. • Pt. received 1 unit of platelets (post-transfusion count: 13.3 • 1 week following, platelet count 383.

11. Case 1 Diagnosis: • Drug-induced thrombocytopenia: • The main differential diagnosis in a drug-induced thrombocytopenia is ITP. • Drug exposure is the cause of 5-20% of thrombocytopenias • Typically see the effect approximately 14 days after starting the medication

12. Drug-Induced Thrombocytopenia • Mechanism of various blood dyscrasias due to drugs: • Interference with hematopoiesis, bone marrow suppression • Drug induced antibodies • Commonly seen with the psychotropic drugs, quinidine, sulfonamides, and gold • Study by Stübner et al (2004), found that clozapine was most common psychotropic drug to cause blood dyscrasias (0.18%) followed by carbamazepine (0.14%).

13. Drug-Induced Thrombocytopenia • Mechanisms of drug-dependent antibody formation: • Accelerated platelet destruction due to drug-dependent antibody • Reversible drug binding to one of the platelet surface glycoproteins (GP Ib/IX, GP IIb/IIIa) causing conformational change, resulting in the exposure of a neoepitope, expressed by a sequence that is normally concealed within the hydrophobic domain of the protein. • Molecular structure of the drug becomes an integral part of the new antigenic epitope • There are no good laboratory tests to detect these drug-induced antibodies.

14. Drug-Induced Thrombocytopenia • Criteria to make diagnosis: • 1) Candidate drug preceded thrombocytopenia AND recovery from thrombocytopenia was complete and sustained after the drug was discontinued. • 2) The candidate drug was the only drug used prior to the onset of thrombocytopenia OR other drugs were continued or reintroduced after discontinuation of the candidate drug with a sustained normal platelet count. • 3) Other etiologies for thrombocytopenia were excluded. • 4) Reexposure to the candidate drug resulted in recurrent thrombocytopenia. • Definite (Level 1): meet criteria 1, 2, 3, 4 • Probable (Level 2): meet criteria 1, 2, 3

15. Drug-Induced Thrombocytopenia • Thrombocytopenia associated with carbamazepine usually appears 14 to 16 days after initiation of drug. The platelet count completely resolved in all cases 7 days after after the drug was discontinued. • Gold induced thrombocytopenia doesn’t follow this pattern, have persistently low platelets for months because of prolonged retention of gold salts

16. Case 2

17. Case 2 • 24 year old African American female presented with complaints of: • Easy bruising x 1 month • Heavy menses • 1-2 episodes of fever in the past month • 2 days of cervical lymphadenopathy (resolved) • Occasional night sweats • No weight loss

18. Case 2 • Initial laboratory findings: • WBC: 3.15 x 1000/μL (4.5 – 11.0) • RBC: 3.26 M/μL (4.6 – 6.2) • Plt: 3.16 x 1000/μL (150 – 400) • Hgb: 8.80 g/dL (14.5 – 18.1) • Hct: 26.7% (42 – 54) • MCV: 81.8 fL (80 – 100) • MCH: 27.0 pg (28 – 34) • RDW: 16.1% (11.5 – 14.5) • Abs Neutrophil: 1.63 x 1000/μL (1.8 – 7.8)

19. Case 2 • Smear

20. Case 2 • Differential diagnosis of pancytopenia with severe thrombocytopenia: • Marrow infiltrative process (i.e. leukemia, lymphoma, metastatic disease) • Idiopathic Thrombocytopenic Purpura (ITP) • Why the neutropenia and anemia? • Next step, bone marrow biopsy.

23. Case 2 Diagnosis: • ITP • Iron deficiency anemia, secondary to menometrorrhagia from low platelets • Benign neutropenia of African Americans • Low absolute neutrophil count seen in African Americans. No increased risk of infection.

24. Case 2 • Patient received steroids, IVIG x1, platelet transfusions. • 1 week following, repeat CBC with a platelet count of 35

25. ITP Epidemiology of ITP: • Incidence of 3-5 per cases 100,000 persons • Onset typically adults aged 20-40 years • Female predominance

26. ITP • Differential diagnosis: • Diagnosis of exclusion, need to exclude drug-induced thrombocytopenia • Familial thrombocytopenia • Check family history of low platelets unresponsive to treatment for ITP • HIV-ITP • Thrombotic thrombocytopenic purpura (TTP) • Spurious thrombocytopenia resulting from platelet clumping • Always look at the peripheral smear of a patient with thrombocytopenia

27. ITP • Mechanism: • Patients platelets are coated with IgG antibodies the recognize the platelet surface glycoproteins. Tissue macrophages recognize the Fc receptor, and phagocytose the platelet-AB complex. • May also have reduced megakaryocyte production secondary to autoantibodies against megakaryocytes. • Most frequent target antigens include GP Ib/IX/V and GP IIb/IIIa

28. ITP Diagnosis: • Diagnosis of exclusion • Should exclude other causes of thrombocytopenia • Review the peripheral smear • Bone marrow examination if atypical • Detection of anti-platelet antibodies(49-66% sensitive, 78-92% specific, interlaboratory agreement 55-67%) (not readily used) • Flow cytometry to detect platelet associated autoantibodies (still being investigated but may be promising)

29. ITP • Diseases and disorders associated with ITP: • HIV • Circulating immune complexes may nonspecifically deposit on platelet membrane, and are then cleared from system • Direct infection of megakaryocytes by HIV infection impairs platelet production • Hepatitis C • ?? H. pylori (still being debated) • Thought is that some strains of H. Pylori express the Lewis (Le) antigen. The Le antigen may adsorb the the platelet surface and serve as a target for anti-Le antibodies. • SLE • The patient had elevated ANA titer (1:2500) (still to be worked up)

30. ITP Treatment: • Steroids • Anti-D • Use in Rh+ patients. The Anti-D will coat the patient’s RBC, so that the IgG coated RBC compete with the IgG coated platelets for phagocytosis from the spleen, blocking splenic destruction of platelets. • IVIG • Splenectomy if refractory to treatment

31. Case 3

32. Case 3 • 76 year old male with 80-90% stenosis of left main coronary artery, 70% stenosis of left anterior descending coronary artery • Underwent Coronary Artery Bypass Graft (CABG)

33. Case 3 • Platelet counts: • Pre-op: 169 x 1000/μL (150 – 400) • Day of surgery: 110 • POD #1: 104 • POD #2: 74.7 • POD #3: 92.2 • POD #4: 81.5 • POD #5: 89.8 • POD #6: 52.3 • POD #7: 11.3 • POD #8: 8.86

34. Case 3 • Patient received heparin prior to and during surgery, with no documentation of heparin received post-operatively. • No clinical evidence of clotting.

35. Case 3 • Differential diagnosis: • Heparin-induced thrombocytopenia (HIT) • Other drug-induced thrombocytopenia • ITP • DIC • TTP

36. Case 3 Diagnosis: • Heparin-induced thrombocytopenia • ELISA test positive

37. Case 3 • Patient was switched to Argatroban, all heparin was discontinued • Platelet count increased to 231 • No thrombotic events

38. HIT • Occurs as a result of an antibody complex between heparin and platelet factor 4 • IgG antibodies bind to the platelet Fc receptor and cause platelet activation, resulting in platelet activation as well as clearance from circulation.

39. HIT

40. HIT • Diagnosis: • Diagnosis rests primarily on clinical grounds • Laboratory tests not always locally available. • Lab tests may not be available in timely manner • Available tests are not completely sensitive or specific.

41. HIT Clinical diagnosis (Four T’s): • Thrombocytopenia: >50% fall in platelet count • Timing: Days 5-10 after exposure to heparin, or <day 1 with recent heparin exposure (past 30 days) • Thrombosis: Proven new thrombosis; skin necrosis; acute systemic reaction after IV heparin • OTher causes of platelet fall excluded

42. HIT • Functional assay: Utilize the ability of the antibody to cause platelet activation as an endpoint. • Require source of normal human platelets with variability • See platelet activation at therapeutic concentration of heparin, but not at markedly therapeutic levels

43. HIT • Functional assays: • Serotonin release assay. Most sensitive and specific of the functional assays • Incubate washed platelets with radiolabeled serotonin. Metabolically active platelets tae up serotonin and store it in their granules. • “Hot” platelets incubated with patient’s serum in the presence and absence of heparin at therapeutic and supratherapeutic levels. • Measure radioactivity in supernatant. Positive if: • >20% release at therapeutic heparin level • <20% release at supratherapeutic levels • 99% specificity, high sensitivity • Very few labs perform because of technical difficulty and use of radioactive substances.

44. HIT • Functional assays: • ATP release via luminescence aggregometry • Closely resembles SRA as alternative approach • Able to detect ATP release of activated platelets • Platelet aggregation studies: • Donor platelets incubated with patient’s serum and heparin. Measure donor platelets aggregation without heparin, with therapeutic levels of heparin, and with supratherapeutic heparin • Highly dependent on donor platelets • Sensitivity 39-81% • Specificity 82%

45. HIT • Immunological Assays: • ELISA to detect the Heparin-PF4 antibody • Does not require normal platelets, technically easier to perform • High false positive rate, low specificity • 50-60% patients undergoing open heart surgery will have a positive ELISA in the absence of clinical HIT • Commercially available assay detects IgG, IgA, and IgM heparin-PF4 antibodies • Unlikely that IgM would cause clinical disease

46. HIT • Immunologic Assays: • ELISA (cont’d): • Does have higher sensitivity than aggregation studies • ELISA for HIT may initially be negative at time first clinically suspect HIT, but that a portion of those may then develop a positive ELISA if the test is repeated based on persisting clinical suspicion. • May have false negative because HIT is due to an antigen other than PF4

47. HIT • No laboratory test is 100% specific or sensitive for HIT • Interpret results in light of the pretest probability. Should only be performed when there is a clinical indication of HIT

48. HIT • Treatment: • Discontinue all heparin and low molecular weight heparin • Use alternative anticoagulant (direct thrombin inhibitor): • Argatroban • Lepirudin

49. The End