Antiphospholipid Syndrome and Thrombosis

 

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Abstract

Antiphospholipid antibodies [such as anticardiolipin antibodies (ACLA)] are strongly associated with thrombosis and appear to be the most common of the acquired blood protein defects causing thrombosis. Although the precise mechanism(s) whereby antiphospholipid antibodies alter hemostasis to induce a hypercoagulable state remain unclear, several theories have been advanced. The most common thrombotic events associated with ACLA are deep vein thrombosis and pulmonary embolus (type I syndrome), coronary or peripheral artery thrombosis (type II syndrome) or cerebrovascular/retinal vessel thrombosis (type III syndrome), and occasionally patients present with mixtures (type IV syndrome). Type V patients are those with antiphospholipid antibodies and fetal wastage syndrome. It is as yet unclear how many seemingly normal individuals who may never develop manifestations of antiphospholipid syndrome (type VI) harbor asymptomatic antiphospholipid antibodies. The relative frequency of ACLA in association with arterial and venous thrombosis strongly suggests that these should be looked for in any individual with unexplained thrombosis; all three idiotypes (IgG, IgA, and IgM) should be assessed. Also, the type of syndrome (I through VI) should be defined, if possible, as this may dictate both type and duration of both immediate and long-term anticoagulant therapy. Unlike those with ACLA, patients with primary lupus anticoagulant thrombosis syndrome usually suffer venous thrombosis. Because the activated partial thromboplastin time (aPTT) is unreliable in patients with lupus anticoagulant (prolonged in only about 40 to 50% of patients) and is not usually prolonged in patients with anticardiolipin antibodies, definitive tests including ELISA for ACLA, the dRVVT for lupus anticoagulant, hexagonal phospholipid neutralization procedure, and B-2-GP-I (IgG, IgA, and IgM) should be immediately ordered when suspecting antiphospholipid syndrome or in individuals with otherwise unexplained thrombotic or thromboembolic events. If these are negative, in the appropriate clinical setting, subgroups should also be assessed. Finally, most patients with antiphospholipid thrombosis syndrome will fail warfarin therapy and, except for retinal vascular thrombosis, most will fail antiplatelet therapy, thus it is of major importance to make this diagnosis in order that patients can be treated with the most effective therapy for secondary prevention, low-molecular weight heparin (LMWH) or unfractionated heparin (UHF) in most instances.