1) Differential for acute bloody diarrhea includes (and complications):
- Infectious etiologies: Camplobacter (Gullian Barre Syndrome), Shigella, Non-typhoidal Salmonella (bacteremia and aortitis), enterohemorrhagic or enteroinvasive E. coli (hemolytic uremic syndrome), C. difficile, Vibrio parahemolyticus, Entamoeba histolytica (liver abscess), and CMV
- Noninfectious etiologies: diverticular disease, rectal or colonic malignancy, inflammatory bowel disease, ischemic colitis, intussusception
2) Thrombotic microangiopathy (TMA) is a subset of microangiopathic hemolytic anemia (MAHA). MAHA is a term for non-immune mediated hemolytic anemia resulting from intravascular RBC fragmentation that produces shistocytes on the peripheral blood smear--and can occur due to abnormalities in the microvasculature or due to intravascular devices (such as valves or LVADs).
TMA is caused by abnormalities in the vessel wall of arterioles and capillaries leading to microvascular thrombosis and is divided into primary and secondary syndromes.
- Primary TMA: Thrombotic thrombocytopenic purpura (TTP), Shiga-toxin mediated hemolytic uremia syndrome ( ST-HUS), Complement-mediated, and Drug-induced (especially quinines) are the most common in adults
- Systemic disorders associated with TMA: DIC, Preeclampsia and HELLP, severe hypertension, systemic infections, malignancies, rheumatic disorders, stem cell or organ transplantation, severe B12 deficiency
3) Management of primary TMAs is determined by the cause.
- plasma exchange (if you are highly suspicious of TTP and ADAMSTS13 deficiency)
- eculizumab (if complement-mediated TMA is suspected)
- drug-withdrawal (if drugs are suspected cause)
- otherwise, care is supportive
4) The use of antibiotics and the associated risk of development of HUS-TTP is addressed in this 2016 meta-analysis in Clinical Infectious Diseases. The bottom line is: antibiotics are not recommended in patient's with shiga-toxin producing E. coli.