20-09: Antiphospholipid Syndrome

GENERAL CONSIDERATIONS

Primary antiphospholipid syndrome (APS) is diagnosed in patients who have venous or arterial occlusions or pregnancy complications (ie, three or more first-trimester miscarriages, unexplained fetal death, and premature birth before 34 weeks of gestation attributable to severe preeclampsia, eclampsia, or placental insufficiency) with persistent (12 weeks or longer), high-titer, diagnostic antiphospholipid antibodies but no other features of SLE (see Chapter 19). Diagnostic antiphospholipid antibodies are IgG or IgM anticardiolipin, or IgG or IgM antibodies to beta-2-glycoprotein 1, and lupus anticoagulant. In less than 1% of patients with antiphospholipid antibodies, a potentially devastating syndrome known as the “catastrophic antiphospholipid syndrome” occurs, leading to diffuse thromboses, thrombotic microangiopathy, and multiorgan system failure.

CLINICAL FINDINGS

A. Symptoms and Signs

Patients are often asymptomatic until suffering a thrombotic complication of this syndrome or a pregnancy loss. Thrombotic events may occur in either the arterial or venous circulations. Thus, deep venous thromboses, pulmonary emboli, and cerebrovascular accidents are typical clinical events. Budd-Chiari syndrome, cerebral sinus vein thrombosis, myocardial or digital infarctions, hemorrhagic infarction of the adrenal glands (due to adrenal vein thrombosis), and other thrombotic events also occur. Other symptoms and signs of APS include thrombocytopenia, mental status changes, livedo reticularis, skin ulcers, microangiopathic nephropathy, and cardiac valvular thickening or vegetations. Pregnancy losses that are associated with APS include unexplained fetal death after the first trimester, one or more premature births before 34 weeks because of eclampsia or preeclampsia, or three or more unexplained miscarriages during the first trimester.

B. Laboratory Findings

As noted above, three types of antiphospholipid antibodies are associated with this syndrome: (1) anti-cardiolipin antibodies, (2) antibodies to beta-2-glycoprotein, and (3) a “lupus anticoagulant” that prolongs certain phospholipid-dependent coagulation tests (see below). Antibodies to cardiolipin and to beta-2-glycoprotein are typically measured with enzyme immunoassays. Anti-cardiolipin antibodies can produce a biologic false-positive test for syphilis (ie, a positive rapid plasma reagin but negative specific anti-treponemal assay). In general, IgG anti-cardiolipin antibodies are believed to be more pathologic than IgM. In case-control studies, 3.1% of patients in the general population who experienced a venous thrombotic event (in the absence of cancer) tested positive for the lupus anticoagulant (versus 0.9% of controls, yielding an odds ratio of 3.6). For women younger than 50 years in whom stroke developed, the odds ratio for having the lupus anticoagulant is 43.1. Presence of the lupus anticoagulant is a stronger risk factor for thrombosis or pregnancy loss than is the presence of antibodies to either beta-2-glycoprotein 1 or anticardiolipin. A clue to the presence of a lupus anticoagulant, which may occur in individuals who do not have SLE, may be detected by a prolongation of the partial thromboplastin ...