Differential Diagnosis for Low Platelets, Fever, and Rash

• Single most likely diagnosis
  • Thrombotic Thrombocytopenic Purpura (TTP): This condition is characterized by low platelet count, fever, rash, and microangiopathic hemolytic anemia. The presence of these symptoms together makes TTP a strong candidate for the single most likely diagnosis.
• Other Likely diagnoses
  • Immune Thrombocytopenic Purpura (ITP): Although ITP primarily presents with isolated thrombocytopenia, some cases can be associated with fever and rash, especially if there's an underlying infection or autoimmune disorder.
  • Systemic Lupus Erythematosus (SLE): SLE can cause a wide range of symptoms including thrombocytopenia, fever, and rash due to its autoimmune nature.
  • Viral infections (e.g., HIV, Epstein-Barr virus): Certain viral infections can lead to thrombocytopenia, fever, and rash, making them plausible diagnoses.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Meningococcemia: This condition, caused by Neisseria meningitidis, can present with fever, rash, and thrombocytopenia. It's critical to consider due to its high mortality rate if not promptly treated.
  • Disseminated Intravascular Coagulation (DIC): Although DIC can present with a variety of symptoms, the combination of thrombocytopenia, fever, and rash could be indicative of this condition, especially in the context of severe infection or trauma.
  • Hemolytic Uremic Syndrome (HUS): Similar to TTP, HUS involves microangiopathic hemolytic anemia and thrombocytopenia but is more commonly associated with renal failure. It's essential to differentiate HUS from TTP due to differences in management.
• Rare diagnoses
  • Dengue Fever: In rare cases, dengue fever can cause severe thrombocytopenia, along with fever and rash. It's more likely to be considered in patients with travel history to endemic areas.
  • Thrombocytopenia with Absent Radius (TAR) syndrome: This is a rare genetic disorder that could potentially present with thrombocytopenia and might be associated with fever and rash in the context of an infection or other complicating factors.
  • Kawasaki Disease: Although primarily seen in children, Kawasaki disease can cause fever, rash, and thrombocytopenia in its later stages, making it a rare but possible diagnosis to consider in pediatric patients.