Mechanism: drug-induced antiplatelet antibodies
- Antibodies bind to complexes of heparin and platelet factor 4 (PF4)
- Crosslinks FcyRII receptors on platelets
- → induce platelet aggregation and consumption
Epidemiology
- Risk: unfractioned heparin >> low molecular weight heparin
Clinical presentation
- thrombosis and cutaneous necrosis at distant sites and internal organs (CNS)
- arterial, venous and microvascular occlusion
- non-inflammatory retiform purpura
- non-inflammatory necrosis
- cutaneous lesions may arise locally at sites of heparin infusion or at distant sites
- necrotic skin lesions at heparin injection sites
- onset between D5 and D10 of heparin therapy
Associations:
- main are sulfa-drugs, antibiotics, heparin
Labs
- Not needed to start treatment
- Thrombocytopenia (compare with previous labs)
- >50% of recent highest count
- Detect Ab’s via 14C serotonin release assay (functional assay)
- Detection of anti-PF4-heparin complex antibodies by ELISA (high negative predictive value but low positive predictive value)
Histology
- Non-inflammatory occlusion of blood vessels and ischemic necrosis
Treatment
- Discontinue heparin
- May switch to hirudin or warfarin
- Substitute with other anticoagulants (argatroban, bivalirudin)
- Corticosteroids
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