ANTIPHOSPHOLIPID SYNDROME
Definition
Antiphospholipid syndrome (APS) is a disorder characterised by recurrent venous or arterial thrombosis and/or foetal losses associated with typical laboratory abnormalities. These include persistently elevated levels of antibodies directed against membrane anionic phospholipids (i.e., anticardiolipin [aCL] antibody, antiphosphatidylserine) or their associated plasma proteins, predominantly beta-2 glycoprotein I (apolipoprotein H), or evidence of a circulating anticoagulant. It is generally regarded as being a T-helper 2 dominant condition.
Aetiology / Risk Factors
An alteration of the homeostatic regulation of blood coagulation occurs; however, the mechanisms of thrombosis are not yet defined. One hypothesis postulates a defect in cellular apoptosis, which exposes membrane phospholipids to the binding of various coagulation proteins. Once bound, a phospholipid-protein complex is formed and a neoepitope is uncovered, which subsequently becomes the target of autoantibodies.
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Actual frequency in the general population is unknown. aPL antibodies can be found in as many as 50% of individuals with SLE and in 1-5% of the healthy population. aCL antibody tends to occur more frequently in elderly individuals. Recent literature suggests that the occurrence rate of APS in patients with SLE is 34-42%.
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No defined racial predominance is documented for primary APS, although a higher prevalence of SLE occurs in African American and Hispanic populations.
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A female predominance is documented, particularly for secondary APS. This parallels the association of APS with SLE and other connective-tissue diseases, which also have a female predominance.
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APS occurs more commonly in young-to-middle–aged adults; however, it also manifests in children and elderly people. Disease onset has been reported in children as young as 8 months.
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Familial association: Relatives of persons with known APS are more likely to have aPL antibodies. One study showed a 33% incidence rate.
Symptoms & Signs
The series of events that leads to hypercoagulability and recurrent thrombosis can affect the extremities and virtually any organ system, including the following:
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Peripheral venous system (deep venous thrombosis [DVT])
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Central nervous system (cerebrovascular accident [CVA], sinus thrombosis)
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Haematologic (thrombocytopenia, haemolytic anaemia)
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Obstetric (pregnancy loss, eclampsia)
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Pulmonary (pulmonary embolism, pulmonary hypertension)
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Dermatologic (livedo reticularis, purpura, infarcts/ulceration)
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Cardiac (Libman-Sacks valvulopathy, myocardial infarction)
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Ocular (amaurosis, retinal thrombosis)
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Adrenal (infarction/haemorrhage)
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Musculoskeletal (avascular necrosis of bone)