USMLE Blog

Featured Posts
Search By Tags

Recall the FAT RN...TTP vs HUS!

Test writers love topics which incorporate multiple systems and basic science topics. They also love to test the differences between two similar syndromes. Thrombotic Thrombocytopenic Purpura (TTP) is one of those, especially in comparison to Hemolytic Uremic Syndrome (HUS). This one is worth spending a little time on.

Here is the quick run down on TTP:

TTP is highly fatal (>90%) if left untreated.

Pathology: Insufficient ADAMTS-13 activity (usually due to anti-ADAMTS13 autoantibodies) leading to large uncleaved vWF multimers to accumulate in microcirculation and ultimately platelet aggregation, thrombocytopenia and hemolysis of RBCs. Multimers of vWF usually remain silent until presented with an insult such as pregnancy, infection, inflammation, or medications (board favorite is clopidogrel or a quinolone).

Classical pentad of TTP:

1. Microangiopathic Hemolytic Anemia (MAHA)

2. Thrombocytopenia

3. Fever

4. Renal pathology

5. CNS abnormalities (headache, seizure, altered mental status, CVA, coma)

These can be remembered with the mnemonic: “FAT RN”, recall: you get called by this FAT Registered Nurse telling you about the patient with Fever, Anemia, Thrombocytopenia, Renal issues and Neurological Symptoms

Treat the combination of MAHA and low platelets as TTP unless proven otherwise. Platelet clots are transient and the associated symptoms especially neuro, may wax and wane.

TTP is often paired with the distractor of HUS and vice versa. Know how to tell them apart!

HUS follows infection with Enterohemorrhagic E. coli (EHEC) but the question writer will very rarely hand you E. Coli on a silver platter. Watch for a young kid that has eaten an undercooked burger and develops a bloody diarrheal illness, MAHA, and thrombocytopenia.

To remember HUS look at this image

  • There will probably be a story about eating poorly prepared food, usually ground beef.

  • Signs of microangiopathic hemolysis: anemia with schistocytes on a peripheral smear, and labs suggesting hemolysis (increased bilirubin, jaundice)

  • Uremia/Kidney Failure

Recent Posts