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The antiphospholipid (aPL) syndrome (APS) is an acquired thrombophilic disorder in which patients have vascular thrombosis and/or pregnancy complications attributable to placental insufficiency, accompanied by laboratory evidence for the presence of antiphospholipid antibodies in blood. The disorder is referred to as primary APS when it occurs in the absence of systemic lupus erythematosus (SLE), and secondary APS in its presence. Although the most frequently affected vessels are the deep veins of the lower extremities, any portion of the circulatory tree can be affected. Abnormalities that have been reported in association with the syndrome include virtually all other autoimmune disorders, immune thrombocytopenia, acquired platelet function abnormalities, hypoprothrombinemia, acquired inhibitors of coagulation factors, livedo reticularis, heart valve abnormalities, atherosclerosis, pulmonary hypertension, migraine, and sensorineural hearing loss. Rare patients have a catastrophic form of APS (CAPS) in which there is disseminated thrombosis in large- and small-vessel thrombi, often after a triggering event such as infection or surgery, and often with multiorgan ischemia and infarction.

The main antigenic targets for thrombogenic aPL antibodies are not phospholipids. Rather, they are epitopes on phospholipid-binding proteins, the most important of which appears to be β2-glycoprotein I (β2GPI). The syndrome is identified by persistent abnormalities of laboratory tests for antibodies against these phospholipid–protein cofactor complexes, detected by immunoassays and by coagulation assays that, paradoxically, report the inhibition of phospholipid-dependent coagulation reactions. Several conditions, including syphilis, Lyme disease, hepatitis C, alcoholic liver disease, HIV infection, and multiple sclerosis, are associated with increased levels of aPL antibodies that are generally not thrombogenic and are directed against anionic phospholipids themselves rather than the protein cofactors. Long-term warfarin anticoagulant therapy is the usual treatment for thrombosis in patients with APS, although there is some controversy regarding treatment of patients with stroke. Patients with recurrent spontaneous pregnancy losses and APS generally are treated with aspirin and heparin during their pregnancies for prophylaxis against deep vein thrombosis during the postpartum period. CAPS patients have a high mortality and often require additional therapy with anticoagulants, plasmapheresis, and immunosuppressive agents. Patients without clinical manifestations of APS or SLE, should generally not undergo diagnostic screening and, if tested and found to be positive, should not be committed to antithrombotic therapy for the laboratory abnormalities alone. Where anticoagulant therapy is indicated, care should be taken to confirm that prothrombin time and international normalized ratio determinations for monitoring oral anticoagulant therapy reflect true reductions in the levels of the vitamin K-dependent coagulation proteins and are not artifactually altered by a lupus anticoagulant.

Acronyms and Abbreviations

Acronyms and abbreviations that appear in this chapter include: aCL, anticardiolipin; APASS, Antiphospholipid Antibodies and Stroke Study; APC, activated protein C; aPL, antiphospholipid; APS, antiphospholipid syndrome; aPTT, activated partial thromboplastin time; ARDS, acute respiratory distress syndrome; AVWS, acquired von Willebrand syndrome; BFP syphilis test, biologic false-positive serologic test for syphilis; β2GPI, β2-glycoprotein I; CAPS, catastrophic APS; CMV, cytomegalovirus; dRVVT, dilute Russell viper venom ...

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