Activity Restrictions for Infectious Mononucleosis
Patients with infectious mononucleosis should avoid contact sports and strenuous exercise for at least 4 weeks (and ideally up to 8 weeks) after symptom onset, or until splenomegaly has completely resolved, to minimize the risk of splenic rupture. 1
Rationale for Activity Restriction
The primary concern driving activity restriction is splenic rupture, which occurs in 0.1-0.5% of patients with infectious mononucleosis and is potentially life-threatening. 1, 2 Critically, 90.5% of splenic injuries occur within 31 days of symptom onset, but only 73.8% occur within the traditional 21-day restriction period—meaning a substantial number of ruptures happen between days 21-31. 3 This evidence suggests current 3-week guidelines may be insufficient.
Specific Activity Restriction Timeline
Minimum Restriction Period
- Avoid all contact sports and strenuous exercise for 4 weeks minimum after symptom onset 1
- Optimal restriction extends to 8 weeks or until splenomegaly resolves completely 1
- Consider extending to 31 days for high-risk athletes in contact sports, given the timing data on splenic rupture 3
Prerequisites Before Returning to Activity
Before any return to sports, patients must be: 4
- Afebrile (no fever)
- Well hydrated
- Asymptomatic (no fatigue, pharyngitis, or other symptoms)
- No palpable splenomegaly or hepatomegaly on physical examination
Important Caveat on Physical Examination
Clinical examination for splenomegaly is notoriously unreliable—the standard deviation of normal splenic measurements matches the typical size increase seen in infectious mononucleosis. 2 Physical exam alone cannot guarantee the spleen has returned to normal size and compliance. 4
Graded Return to Activity Protocol
After meeting the above prerequisites at 4-8 weeks, implement a graded reconditioning program over 2-3 months: 2
- Begin with light aerobic activity (walking, light cycling)
- Progressively increase intensity over several weeks
- Monitor for recurrence of symptoms, particularly fatigue
- Full athletic performance typically returns within 2-3 months of conservative management 2
Role of Imaging for Earlier Return
For athletes in contact sports who wish to return earlier than 4 weeks, or those with equivocal physical examination: 4
- 2D ultrasonography can assess splenic size objectively
- Must account for methodology, calculation formulae, and individual body size 2
- Repeat measurements help monitor disease regression 2
- However, no strong evidence supports using imaging alone to predict safe return 4
Critical Warning Signs Requiring Immediate Evaluation
Acute abdominal pain signals possible splenic rupture—this is a medical emergency. 2 Four young patients with infectious mononucleosis in one series bled to death at home from ruptured spleens. 5
Risk of Chronic Fatigue
Progression to chronic fatigue syndrome is a significant risk that is best avoided through 3-4 weeks of restricted activity followed by graded reconditioning. 2 Premature return to intense activity increases this risk substantially.
Common Pitfalls to Avoid
- Do not rely solely on symptom resolution to clear athletes—splenomegaly may persist asymptomatically 1
- Do not use the traditional 3-week restriction for contact sport athletes—extend to at least 4 weeks, preferably 8 weeks 1
- Do not assume normal physical exam means normal spleen—clinical palpation misses many cases of persistent splenomegaly 2
- Do not allow return to full-intensity training immediately—use graded progression over weeks 2