Anti-phospholipid antibody syndrome has primary and secondary forms. Individuals with a well-defined autoimmune disease, such as systemic lupus erythematosus (Chapter 5), are designated as having secondary antiphospholipid syndrome (hence the earlier term lupus anticoagulant syndrome). In primary anti-phospholipid syndrome, patients exhibit only the manifestations of a hypercoagulable state and lack evidence of other autoimmune disorders; occasionally, it appears following exposure to certain drugs or infections. Therapy involves anticoagulation and immunosuppression. Although antiphospholipid antibodies are clearly associated with thrombotic diatheses, they have also been identified in 5% to 15% of apparently normal individuals, implying that they are necessary but not sufficient to cause the full-blown syndrome.
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Fig. 4.13 Muralthrombi.(A)Thrombusintheleftandrightventricularapices,overlyingwhitefibrousscar.(B)Laminatedthrombusinadilatedabdominalaorticaneurysm.Numerousfriablemuralthrombiarealsosuperimposedonadvancedatheroscleroticlesionsofthemoreproximalaorta
Thrombicandevelopanywhereinthecardiovascularsystem.Arterialorcardiacthrombitypicallyariseatsitesofendothelialinjuryorturbulence;venousthrombicharacteristicallyoccuratsitesofstasis.Thrombiarefocallyattachedtotheunderlyingvascularsurfaceandtendtopropagatetowardtheheart;thus,arterialthrombigrowinaretrogradedirectionfromthepointofattachment,whereasvenousthrombiextendinthedirectionofbloodflow.Thepropagatingportionofathrombustendstobepoorlyattachedandthereforepronetofragmentationandmigrationthroughthebloodasanembolus.
Thrombicanhavegrossly(andmicroscopically)apparentlaminationscalledlines of Zahn; theserepresentpaleplateletandfibrinlayersalternatingwithdarkerredcell–richlayers.Suchlinesaresignificantinthattheyareonlyfoundinthrombithatforminflowingblood;theirpresencecanthereforeusuallydistinguishantemortemthrombosisfromtheblandnonlaminatedclotsthatforminthepostmortemstate.Althoughthrombiformedinthe“low-flow”venoussystemsuperficiallyresemblepostmortemclots,carefulevaluationgenerallyshowsill-definedlaminations.
Thrombioccurringinheartchambersorintheaorticlumenaredesignatedasmural thrombi. Abnormalmyocardialcontraction(arrhythmias,dilatedcardiomyopathy,ormyocardialinfarction)orendomyocardialinjury(myocarditis,cathetertrauma)promotecardiacmuralthrombi(
Fig.4.13A ),whereasulceratedatheroscleroticplaquesandaneurysmaldilationpromoteaorticthrombosis(
Fig.4.13B