Antiphospholipid syndrome

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Antiphospholipid syndrome


Coagulation disorders


Vitamin K deficiency

Leukemoid reaction

Leukemoid reaction


Antiphospholipid syndrome


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USMLE® Step 1 questions

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High Yield Notes

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Antiphospholipid syndrome

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USMLE® Step 1 style questions USMLE

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A 52-year-old woman, para 4 gravida 2 aborta 2, comes to the clinic for a follow-up appointment after a hospitalization. Two weeks ago, she had an incident of acute, severe abdominal pain and bloody stools. She was diagnosed with portal vein thrombosis. She denies similar episodes in the past. Medical history is notable for Legg-Calvé-Perthes disease as a child. She does not smoke, drink excessive alcohol, or use illicit drugs. She had 2 spontaneous abortions in the first trimester, following 2 successful pregnancies. Family history is remarkable for DVT in her maternal uncle and colon cancer in her father. The physician suspects an inherited condition. Which of the following will prompt further evaluation in this patient?  


In antiphospholipid syndrome, individuals produce antiphospholipid antibodies, which attack the phospholipids in the cell membrane of their own cells, or attack proteins that are bound to those phospholipids.

So antiphospholipid syndrome, or APS, is an autoimmune disease.

Antiphospholipid syndrome can be primary or secondary. Primary antiphospholipid syndrome occurs by itself, whereas secondary antiphospholipid syndrome occurs with other autoimmune diseases, especially systemic lupus erythematosus.

And just like most autoimmune diseases, antiphospholipid syndrome is more common in young females.

The exact cause of antiphospholipid syndrome isn’t known, but there are some known genetic and environmental factors.

For instance, the HLA-DR7 gene encodes a specific type of a protein called major histocompatibility complex or MHC class II, which sits on the surface of the B cell.

These surface proteins help activate B cells so that they can start producing antibodies.

Now, having a mutated HLA-DR7 gene predisposes individuals to activate B cell production of antiphospholipid antibodies.

But the presence of the mutated HLA-DR7 gene alone isn’t enough to develop antiphospholipid syndrome - an environmental trigger must also be present.

There’s a variety of potential triggers - some common ones include infections - like syphilis, hepatitis C, HIV, and malaria - drugs, like some cardiovascular drugs - including procainamide, quinidine, propranolol, and hydralazine - or antipsychotic drugs like phenytoin and chlorpromazine.


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  2. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  3. "Harrison's Principles of Internal Medicine" McGraw-Hill Medical Publishing (2004)
  4. "Antiphospholipid syndrome" Best Practice & Research Clinical Rheumatology (2020)
  5. "Antiphospholipid syndrome" Thrombosis Research (2017)
  6. "Diagnosis and Management of the Antiphospholipid Syndrome" New England Journal of Medicine (2018)
  7. "Antiphospholipid syndrome" Translational Research (2020)

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