Vaccine-induced immune thrombotic thrombocytopenia

Background

• Very rare

Clinical Presentation

• Follows recent vaccination within 4 to 30 days
• Can present with severe headache, visual changes, abdominal pain, nause and vomiting, back pain, dyspnea, leg pain or swelling, petechiae and easy bruising

Investigations

• CBC with platelet count and peripheral smear
• Imaging tor thrombosis based on the patient's signs and symptoms
• PF4-ELISA HIT assay, drawn before starting treatment, which is almost always positive with optical density greater than 2
• Fibrinogen, which is often low
• D-dimer, which is usually markedly elevated

Diagnosis

• All four criteria must be met:
  • Recent COVID vaccine within 4 to 30 days previously
    • So far only Johnson & Johnson and AstraZeneca
  • Thrombosis, often cerebral or abdominal
  • Thrombocytopenia, though they may be normal early in the course of illness
  • Positive PF4 HIT ELISA

Management

• Should be started if there are signs or symptoms of serious thrombosis and positive imaging or low platelets
• Treated similarly to heparin-induced thrombocytopenia
  • IVIg 1 g/kg daily for 2 days
  • Non-heparin anticoagulation, such as argatroban, bivalrudin, DOACs, fondaparinux, or danaparoid
  • Thrombocytopenia or low fibrinogen are not absolute contraindications to anticoagulation, especially if platelets are >20 or rising
  • Avoid platelet transfusions, unless serious or life-threatening bleeding