What is the differential diagnosis for a young woman with a 2-week history of fever, cough, rhinorrhea (runny nose), pruritic rash on the face, arms, and torso, accompanied by leukopenia (low white blood cell count) and thrombocytopenia (low platelet count)?

Differential Diagnosis for Young Woman with Fever, Cough, Runny Nose, Pruritic Rash, Leukopenia, and Thrombocytopenia

• Single Most Likely Diagnosis
  • Mononucleosis (infectious mononucleosis caused by Epstein-Barr virus): This diagnosis is likely due to the combination of fever, cough, runny nose, and pruritic rash, along with leukopenia and thrombocytopenia, which are common findings in mononucleosis.
• Other Likely Diagnoses
  • Influenza with secondary bacterial infection: The symptoms of fever, cough, and runny nose could be indicative of influenza, and the addition of a pruritic rash could suggest a secondary bacterial infection.
  • Acute viral exanthem (e.g., roseola, measles, or rubella): These viral infections can cause fever, rash, and respiratory symptoms, and some may also lead to leukopenia and thrombocytopenia.
  • Erythema infectiosum (Parvovirus B19 infection): This viral infection can cause a pruritic rash, fever, and respiratory symptoms, and may also lead to leukopenia and thrombocytopenia.
• Do Not Miss Diagnoses
  • Meningococcemia: Although less likely, this diagnosis is critical to consider due to its high mortality rate if left untreated. The rash in meningococcemia can be pruritic, and the disease can cause fever, cough, and respiratory symptoms.
  • Rocky Mountain spotted fever (RMSF): This tick-borne illness can cause fever, rash, and respiratory symptoms, and can lead to severe complications if not treated promptly.
  • Hemophagocytic lymphohistiocytosis (HLH): This rare but life-threatening condition can cause fever, rash, and cytopenias (including leukopenia and thrombocytopenia), and requires prompt recognition and treatment.
• Rare Diagnoses
  • Lymphoma (e.g., Hodgkin lymphoma or non-Hodgkin lymphoma): Although rare, lymphoma can cause fever, rash, and cytopenias, and should be considered in the differential diagnosis, especially if other diagnoses are ruled out.
  • Leptospirosis: This bacterial infection can cause fever, rash, and respiratory symptoms, and may lead to leukopenia and thrombocytopenia, although it is relatively rare in young women.
  • Idiopathic thrombocytopenic purpura (ITP) with concurrent viral infection: ITP can cause thrombocytopenia, and a concurrent viral infection could explain the other symptoms, although this combination is relatively rare.