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Difficulty: HardFormulating a Differential Diagnosis

Match each clinical presentation of coagulopathy or thrombocytopenia with the most likely underlying diagnosis.

  • A 34-year-old woman with systemic lupus erythematosus presents with a left lower extremity deep vein thrombosis. Laboratory studies show a prolonged aPTT that does not correct upon mixing with normal plasma, normal PT, and a platelet count of 110,000/mm³.Antiphospholipid syndrome
  • A 42-year-old woman with rheumatoid arthritis presents with an acute, expanding spontaneous hematoma of her right thigh. Laboratory studies show a significantly prolonged aPTT that does not correct upon mixing with normal plasma, normal PT, and a platelet count of 250,000/mm³.Acquired hemophilia A
  • A 55-year-old man with Gram-negative bacteremia develops diffuse oozing from venipuncture sites. Laboratory studies show a prolonged PT, prolonged aPTT, a platelet count of 45,000/mm³, low fibrinogen, and schistocytes on peripheral blood smear.Disseminated intravascular coagulation
  • A 28-year-old woman presents with confusion, fever, and petechiae. Laboratory studies show a platelet count of 18,000/mm³, normal PT, normal aPTT, elevated serum creatinine, and schistocytes on peripheral blood smear.Thrombotic thrombocytopenic purpura

Answer

The correct matches differentiate coagulopathies based on clinical presentation (bleeding vs. thrombosis) and the results of specific laboratory tests (PT, aPTT, mixing studies, platelet count, and peripheral smear).
Each clinical scenario presents a distinct combination of symptoms and laboratory findings that point to a specific hematologic etiology. The distinction between an in-vitro inhibitor causing thrombosis (lupus anticoagulant) and an in-vivo inhibitor causing bleeding (acquired hemophilia A) is a key diagnostic concept. Furthermore, distinguishing consumptive coagulopathies based on the integrity of the coagulation cascade (normal in thrombotic thrombocytopenic purpura, severely abnormal in disseminated intravascular coagulation) is essential for formulating an accurate differential diagnosis.

Step-by-Step Solution

1
Analyze the mixing study results for the first two cases with prolonged aPTT.
Both cases show failure to correct, indicating the presence of an inhibitor rather than a factor deficiency.
Normal plasma provides missing factors; failure to correct means an inhibitor is present and interfering with the factors or phospholipids in the assay.
2
Differentiate between the two types of inhibitors based on clinical presentation.
The systemic lupus erythematosus patient has thrombosis (antiphospholipid syndrome with lupus anticoagulant), whereas the rheumatoid arthritis patient has severe bleeding (acquired hemophilia A with Factor VIII inhibitor).
Lupus anticoagulants cause in vitro aPTT prolongation but in vivo hypercoagulability. Specific factor inhibitors cause true in vivo coagulopathy and severe bleeding.
3
Evaluate the cases presenting with severe thrombocytopenia and schistocytes to distinguish the etiology of microangiopathic hemolytic anemia.
The septic patient has prolonged PT and aPTT with low fibrinogen, indicating disseminated intravascular coagulation. The febrile patient has normal PT and aPTT, indicating thrombotic thrombocytopenic purpura.
Disseminated intravascular coagulation systematically consumes both platelets and coagulation factors. Thrombotic thrombocytopenic purpura involves widespread platelet microthrombi without significant consumption of coagulation cascade factors.

Key Concept

Formulating a differential diagnosis for hematologic disorders requires synthesizing clinical clues (bleeding versus clotting, underlying conditions) with distinguishing laboratory patterns (PT, aPTT, mixing studies, platelet counts, and peripheral smears).
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Formulating a Differential Diagnosis

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