Differential Diagnosis

• Single most likely diagnosis
  • Infectious Mononucleosis (IM) caused by a virus other than EBV: The patient has positive heterophile agglutination antibodies but negative EBV antibodies, suggesting an IM-like illness caused by a different virus, such as cytomegalovirus (CMV) or human herpesvirus 6 (HHV-6).
• Other Likely diagnoses
  • Acute viral pharyngitis: The patient's symptoms of sore throat, cough, runny nose, and malaise are consistent with a viral upper respiratory infection.
  • Viral URI (Upper Respiratory Infection): The patient's symptoms of congestion, cough, and runny nose are consistent with a viral URI.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Lemierre's syndrome: A rare but potentially life-threatening condition caused by a bacterial infection, typically Fusobacterium necrophorum, which can present with sore throat, fever, and malaise.
  • Peritonsillar abscess: A serious complication of tonsillitis that can cause severe throat pain, fever, and malaise.
  • Meningitis: A potentially life-threatening infection of the meninges that can present with headache, fever, and malaise.
• Rare diagnoses
  • Toxoplasmosis: A parasitic infection that can cause flu-like symptoms, including sore throat, malaise, and lymphadenopathy.
  • Brucellosis: A bacterial infection that can cause fever, malaise, and lymphadenopathy, although it is relatively rare in the general population.
  • Yersiniosis: A bacterial infection that can cause fever, malaise, and abdominal pain, although it is relatively rare in the general population.