The classic presentation of infectious mononucleosis in children and young adults consists of the triad of fever, pharyngitis, and lymphadenopathy.

The classic presentation of infectious mononucleosis in children and young adults consists of the triad of fever, pharyngitis, and lymphadenopathy. Posterior cervical lymphadenopathy is common and specific for mononucleosis. * Palatal petechiae on the posterior oropharynx distinguishes infectious mononucleosis from other causes of viral pharyngitis. However palatal petechiae can be seen in GABHS pharyngitis, so does not help in distinguishing infectious mononucleosis from that condition. Hepatosplenomegaly also may be present. . Suspicion for this diagnosis usually occurs after a negative rapid strep or throat culture in a patient who is ill for more than seven to 10 days. The monospot test will not become positive until at least seven days into the illness * Common causes of infectious mononucleosis are Epstein-Barr Virus or Cytomegalovirus. * Early in the course of mononucleosis, patients may present with a maculopapular generalized rash. The rash is faint, rapidly disappears, and is nonpruritic. Note that if patients with mononucleosis are misdiagnosed with strep and treated with amoxicillin or ampicillin, 90% will develop a classic prolonged, pruritic, maculopapular rash.