Antiphospholipid syndrome is an autoimmune disorder characterised by arterial and venous thrombosis, adverse pregnancy outcomes (for mother and foetus), and raised levels of antiphospholipid antibodies. While it can occur as a primary condition, it often occurs secondary to systemic lupus erythematosus (SLE).

The main features of APS can be remembered with the mnemonic CLOT:

• Clots - Usually venous thromboembolism (eg. deep venous thrombosis or pulmonary embolism), but arterial embolism (eg. myocardial infarction or stroke) can also occur.
• Livedo reticularis - A mottled, lace-like appearance of the skin on the lower limbs.
• Obstetric loss - Recurrent miscarriages, pre-eclampsia and premature births can occur.
• Thrombocytopenia.

In addition cardiac valve disease can occur, usually aortic and mitral regurgitation ± stenosis.

Investigations

Blood tests:

• One or more of the following positive blood tests are needed on 2 occasions, 12-weeks apart to diagnose APS:
  1. Anti-cardiolipin antibodies.
  2. Anti-beta2 glycoprotein antibodies.
  3. Positive lupus anticoagulant assay.
• Note - syphilis can cause false positive tests for the above, and so should be excluded with treponemal serology.
• FBC - Thrombocytopenia often occurs in APS.
• prolonged APTT
  • A key point for the exam is to appreciate that antiphospholipid syndrome causes a paradoxical rise in the APTT. This is due to an ex-vivo reaction of the lupus anticoagulant autoantibodies with phospholipids involved in the coagulation cascade

Management - based on EULAR guidelines

• primary thromboprophylaxis
  • low-dose aspirin (if not had thrombotic event)