Symptoms of Infectious Mononucleosis in a 14-Year-Old
A 14-year-old with infectious mononucleosis typically presents with the classic triad of fever, tonsillar pharyngitis (sore throat), and cervical lymphadenopathy (swollen lymph nodes in the neck), accompanied by profound fatigue that can last weeks to months. 1, 2
Primary Clinical Manifestations
The presentation in adolescents tends to fit into one of three clinical patterns 3:
Classic Triad (Most Common)
- Fever – often high-grade and persistent 2, 4
- Tonsillar pharyngitis – severe sore throat with tonsillar enlargement, often with exudate 1, 2
- Cervical lymphadenopathy – bilateral, tender, enlarged lymph nodes in the neck 2, 4
Additional Common Symptoms
- Profound fatigue and malaise – this is nearly universal and typically resolves within three months, though it can be the most debilitating symptom 2, 5
- Periorbital or palpebral edema – bilateral eyelid swelling occurs in approximately one-third of patients and is a helpful diagnostic clue 2
- Splenomegaly – enlarged spleen in approximately 50% of cases 2
- Hepatomegaly – enlarged liver in approximately 10% of cases 2
Skin Manifestations
- Maculopapular rash – widely scattered, erythematous rash occurs in 10-45% of cases spontaneously 2
- The rash becomes nearly universal (approaching 100%) if the patient is inadvertently given ampicillin or amoxicillin for presumed streptococcal pharyngitis 3
Clinical Presentation Patterns
Adolescents may present with one of three predominant syndromes 3:
- Pharyngeal form – predominantly sore throat and tonsillar findings
- Glandular form – predominantly lymphadenopathy
- Febrile form – predominantly fever with fewer respiratory symptoms
Laboratory Findings That Support the Diagnosis
- Lymphocytosis – absolute increase in lymphocytes, comprising at least 50% of the white blood cell differential 1, 2
- Atypical lymphocytes – more than 10% of the total lymphocyte count 1, 2
- Elevated liver enzymes – abnormal AST, ALT, and bilirubin in approximately 90% of cases 1, 3
Less Common but Important Manifestations
Neurologic Complications
- Encephalopathy, transverse myelitis, or other neurologic abnormalities can occur but are uncommon 3
Hematologic Complications
- Thrombocytopenic purpura may develop 3
Life-Threatening Complications
- Splenic rupture – occurs in 0.1-0.5% of cases and is the most feared complication, typically occurring in the second or third week of illness 2
- Upper airway obstruction – from massive tonsillar enlargement 3, 6
Important Clinical Caveats
The incubation period is unusually long – approximately six weeks from exposure to symptom onset, which is much longer than typical viral illnesses 5. This means the 14-year-old was likely exposed about 1.5 months before becoming symptomatic.
Heterophile antibody testing (Monospot) is more reliable in adolescents than in younger children, typically becoming positive between days 6-10 after symptom onset 1. However, false-negative results are common in the first week of illness 1.
The illness typically lasts several weeks – most symptoms resolve within 2-4 weeks, though fatigue can persist for three months 2, 4.
Activity Restrictions
Patients must avoid contact sports and strenuous exercise for 8 weeks or while splenomegaly is still present to prevent splenic rupture 1, 2. This is critical counseling for a 14-year-old who may be involved in school athletics.