Infectious Disease · Viral Infections
The facts most likely to be tested
The classic clinical triad of infectious mononucleosis consists of fever, tonsillar pharyngitis, and posterior cervical lymphadenopathy.
The Heterophile Antibody Test (or Monospot test) is the initial diagnostic test of choice, though it may be falsely negative in the first week of illness.
Peripheral blood smear in patients with EBV typically reveals atypical lymphocytes, which are enlarged T-lymphocytes with abundant cytoplasm.
Administration of amoxicillin or ampicillin to patients with EBV frequently results in a characteristic maculopapular rash.
Patients must avoid contact sports for at least 3 to 4 weeks to prevent splenic rupture, the most feared complication of mononucleosis.
EBV infection is strongly associated with the development of Burkitt lymphoma, Hodgkin lymphoma, and nasopharyngeal carcinoma.
Diagnosis is confirmed in heterophile-negative cases by testing for EBV-specific antibodies, specifically viral capsid antigen (VCA) IgM.
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A 19-year-old college student presents with a 5-day history of sore throat, fatigue, and fever. Physical examination reveals exudative tonsillitis, tender posterior cervical lymphadenopathy, and splenomegaly. A rapid streptococcal antigen test is negative. The patient was recently treated for a suspected sinus infection with amoxicillin, which resulted in a diffuse maculopapular rash.
What is the most likely diagnosis?
Infectious mononucleosis (Epstein-Barr Virus)
The patient presents with the classic triad of EBV and a characteristic drug-induced rash following beta-lactam exposure, confirming the diagnosis of infectious mononucleosis.
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Etiology / Epidemiology
Transmitted via saliva (kissing disease) primarily in adolescents and young adults.
Clinical Manifestations
Classic triad: fever, lymphadenopathy (posterior cervical), and pharyngitis.
Diagnosis
Heterophile antibody test (Monospot) is the gold standard for initial screening.
Treatment
Supportive care (rest, fluids, NSAIDs); avoid contact sports due to splenic rupture risk.
Prognosis
Most recover in 2-4 weeks; monitor for splenic rupture and airway obstruction.
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Epidemiology & Etiology
Caused by human herpesvirus 4, transmitted through intimate contact with infected oral secretions. Peak incidence occurs in the 15-24 age group. Most adults have serologic evidence of prior exposure.
Pertinent Anatomy
Infection primarily targets the oropharynx and B-lymphocytes. Significant splenomegaly and hepatomegaly occur due to massive lymphocytic infiltration.
Pathophysiology
EBV infects B-cells, leading to a robust T-cell response (atypical lymphocytes). This immune activation causes the characteristic lymphadenopathy and systemic symptoms. The virus remains latent in B-cells for life.
Clinical Manifestations
Patients present with fever, posterior cervical lymphadenopathy, and severe exudative pharyngitis. A maculopapular rash often develops if the patient is mistakenly treated with amoxicillin or ampicillin. Splenic rupture is a rare but life-threatening emergency presenting with sudden left upper quadrant pain.
Diagnosis
The Heterophile antibody test (Monospot) is the diagnostic test of choice. If negative but suspicion remains high, order EBV-specific antibody titers (VCA IgM/IgG). Peripheral smear will show >10% atypical lymphocytes.
Treatment
Management is strictly supportive care with hydration and antipyretics. Avoid contact sports for at least 3-4 weeks to prevent splenic rupture. Corticosteroids are reserved only for severe cases with airway obstruction or hemolytic anemia.
Prognosis
Fatigue may persist for weeks to months after acute symptoms resolve. Patients must be counseled on the risk of splenic rupture and to seek immediate care for severe abdominal pain.
Differential Diagnosis
Group A Strep: lacks generalized lymphadenopathy and splenomegaly
Cytomegalovirus: usually heterophile-negative mononucleosis
Acute HIV: look for high-risk sexual history and oral ulcers
Toxoplasmosis: often presents with isolated cervical lymphadenopathy
Lymphoma: persistent B-symptoms and non-tender, fixed nodes