Infectious Mononucleosis in a 17-Year-Old: Etiology, History, and Physical Examination Findings
Epstein-Barr virus (EBV) is the causative agent in the vast majority of infectious mononucleosis cases, particularly in adolescents and young adults aged 15-24 years 1.
Most Common Etiologic Agent
EBV, a gamma-herpesvirus, causes infectious mononucleosis in this age group 2, 3. While cytomegalovirus (CMV) can produce a similar mononucleosis syndrome, it is far less common and typically lacks the classic pharyngitis seen with EBV 4. The virus is transmitted primarily through saliva during intimate oral contact, earning its colloquial name "the kissing disease" 3, 5.
Expected Positive Findings in the History of Present Illness
The classic triad consists of fever, tonsillar pharyngitis, and lymphadenopathy 3, 6. In this 17-year-old's HPI, you should specifically document:
Constitutional Symptoms
- Fatigue: Profound and debilitating, though typically resolving within three months 3
- Fever: Often high-grade and persistent 2, 6
- Body aches/myalgia: Commonly reported 2
- Headache: Frequent accompanying symptom 2
Throat Symptoms
- Sore throat: Severe tonsillar pharyngitis is characteristic 6, 5
- Difficulty swallowing: May be present due to pharyngeal inflammation
Timeline
- Incubation period: Approximately 6 weeks from exposure 7
- Symptom onset: Typically gradual over several days
- Exposure history: Contact with ill classmates (as noted in this case) supports person-to-person transmission 3
Important Negative History
The absence of known immunodeficiency, malignancy, or autoimmune disease should be documented, as these would suggest chronic active EBV infection rather than typical infectious mononucleosis 2.
Expected Positive Physical Examination Findings
On examination of this 17-year-old, you should expect to find the following constellation of findings 3, 6:
Lymphatic System
- Posterior cervical lymphadenopathy: Hallmark finding, often bilateral and tender 6, 5
- Generalized lymphadenopathy: May involve anterior cervical, axillary, and inguinal nodes 2
Oropharynx
- Tonsillar pharyngitis: Erythematous, often with exudates 6, 8
- Palatal petechiae: May be present at the junction of hard and soft palate
Abdominal Examination
- Splenomegaly: Present in approximately 50% of cases 3
- Hepatomegaly: Present in approximately 10% of cases 3
- Mild hepatic tenderness: May be present
Dermatologic Findings
- Maculopapular rash: Occurs in 10-45% of cases, typically erythematous and widely scattered 3
- Important pitfall: If ampicillin or amoxicillin is administered (mistaking pharyngitis for streptococcal infection), a florid maculopapular rash develops in up to 90% of patients
- Periorbital/palpebral edema: Bilateral eyelid swelling occurs in one-third of patients and is highly characteristic 3, 4
Vital Signs
- Fever: Often present during examination
- Otherwise stable: Blood pressure and respiratory rate typically normal unless complications present
Laboratory Confirmation
While not part of the physical examination, the diagnosis is supported by:
- Peripheral blood: Leukocytosis with >50% lymphocytes and >10% atypical lymphocytes 1, 3
- Heterophile antibody test (Monospot): Sensitivity 87%, specificity 91% 6
- Caveat: May be falsely negative in the first week of illness 1
- If Monospot negative: EBV viral capsid antigen (VCA) IgM with absent EBNA antibodies confirms acute primary infection 1
Critical Management Considerations
Patients must avoid contact sports and strenuous exercise for 8 weeks from symptom onset or while splenomegaly persists 3, 6 to prevent splenic rupture, which is potentially fatal 8.