Chapter 30-5: Infectious Mononucleosis

TEXTBOOK PRESENTATION

Infectious mononucleosis typically presents with a prodrome of fever, malaise, chills, and sweats. The illness then progresses to the classic triad of severe sore throat, fever (38–40°C), and lymphadenopathy.

DISEASE HIGHLIGHTS

1. Infectious mononucleosis is most common in patients 15–24 years of age (6 to 8 cases/1000 person-years). It is uncommon in adults, accounting for < 2% of pharyngitis in patients over 40 years of age.

2. Infectious mononucleosis is most often caused by EBV (the focus of this discussion) but can be caused by CMV or HHV 6.

3. EBV is spread in saliva.

   1. May be shed in salivary secretions for many weeks

   2. As many as 20% of healthy, previously infected adults intermittently shed virus for decades.

4. Most people are infected with EBV during childhood and the typical childhood infection is subclinical. Less than 10% of children exhibit symptoms.

5. Approximately 90% of adults are EBV seropositive.

EVIDENCE-BASED DIAGNOSIS

1. History

   1. The earliest symptoms of EBV are fever, malaise, chills, and sweats.

   2. These symptoms then progress to the classic triad of severe sore throat, fever, and lymphadenopathy.

2. Physical exam

   1. Common findings include enlarged tonsils; pharyngeal erythema; thick, coating, pharyngeal exudate; palatal petechiae; and tender anterior and/or posterior cervical adenopathy. Posterior cervical adenopathy is quite specific for EBV.

   2. Table 30-4 lists test characteristics for findings suggestive of EBV.

   3. Rash is uncommon in infectious mononucleosis unless there is antibiotic exposure.

      1. 5–10% of patients have a rash of varying morphology

      2. 27–69% of patients with infectious mononucleosis who are treated with amoxicillin or ampicillin develop a rash.

   Infectious mononucleosis is characterized by a triad of fever, sore throat, and lymphadenopathy.

3. Laboratory testing

   1. The heterophile antibody test (Monospot test) is highly specific for EBV.

      1. Specificity, 99%

      2. Sensitivity

         1. False-negative rate in first week is as high as 25%.

         2. 5–10% in second week

         3. 5% in third week of illness

   2. Serum IgM antibody to the EBV viral capsid antigen

      1. Highly accurate test with a longer turnaround time compared to the Monospot test

      2. Test characteristics

         1. Sensitivity, 97%

         2. Specificity, 94%

         3. LR+, 16

         4. LR−, 0.03

      3. This test is useful in patients with suspected infectious mononucleosis who have negative Monospot.

   3. Other tests

      1. Lymphocytosis and the presence of atypical lymphocytes are diagnostically useful.

         1. Lymphocytosis of > 50% on peripheral smear: sensitivity, 66%; specificity, 84%

         2. Atypical lymphocytes > 10% of total lymphocytes: sensitivity, 75%; specificity, 92%

         3. Combination of both lymphocytosis > 50% and atypical lymphocytes > 10%: sensitivity, 43%; specificity, 99%; LR+, 54; LR–, 0.58

      2. Elevated aminotransferases are seen in the majority of patients.