Differential Diagnosis for a 76-year-old Healthy Woman with Acute Diarrhea and Thrombocytopenia

• Single Most Likely Diagnosis

  • Thrombotic Thrombocytopenic Purpura (TTP) or Hemolytic Uremic Syndrome (HUS) due to E. coli O157:H7 infection: This is a likely diagnosis because the combination of acute diarrhea and thrombocytopenia can be seen in these conditions, especially in the context of a possible bacterial infection like E. coli O157:H7, which can cause HUS. TTP, though less common, also presents with thrombocytopenia and can be triggered by various factors including infections.

• Other Likely Diagnoses

  • Viral Gastroenteritis: Certain viral infections can cause both diarrhea and thrombocytopenia, either through direct bone marrow suppression or through an immune-mediated response.
  • Bacterial Gastroenteritis (e.g., Salmonella, Shigella): Similar to viral gastroenteritis, bacterial infections can lead to both symptoms, especially if there's a significant systemic response or toxin production.
  • Medication-induced Thrombocytopenia: If the patient has recently started any new medications, some drugs can cause thrombocytopenia as a side effect, and gastrointestinal upset can be a concurrent symptom.

• Do Not Miss Diagnoses

  • Hantavirus Infection: Though rare, hantavirus can cause a syndrome that includes thrombocytopenia and gastrointestinal symptoms, among others. It's crucial to consider this in the differential due to its severity and potential for outbreak.
  • Severe Infection (e.g., Sepsis): Any severe infection can lead to thrombocytopenia due to consumption of platelets and can also cause diarrhea, either directly or as part of a systemic inflammatory response syndrome (SIRS).
  • Disseminated Intravascular Coagulation (DIC): This condition can present with thrombocytopenia and can be triggered by severe infections, among other causes. It's critical to identify DIC early due to its high mortality rate if not promptly treated.

• Rare Diagnoses

  • Whipple's Disease: A rare, systemic bacterial infection that can cause diarrhea, weight loss, and other systemic symptoms, including potentially thrombocytopenia.
  • Lymphoma or Leukemia: Certain hematologic malignancies can present with thrombocytopenia and gastrointestinal symptoms, though this would be less common as an initial presentation.
  • Tropical Infections (e.g., Dengue Fever): Depending on the patient's travel history, infections like dengue fever can cause thrombocytopenia and gastrointestinal symptoms.