Mononucleosis and Sports Participation

Main symptoms of Infectious mononucleosis This article was originally published at in 2009 and was updated January 20, 2020 The American Medical Society of Sports Medicine had released their 2009 consensus statement, Mononucleosis and Athletic Participation: An Evidence-Based Subject Review. The article discusses mononucleosis and sports participation risks with recommendations for the return-to-play of athletes suffering from mononucleosis. There have been updated recommendations for athlete participation after mononucleosis published in the journal Sports Health in 2014.

What causes Mononucleosis?

Mononucleosis (mono) is a common viral infection in high school and college students that can present with fever, body aches, fatigue, rash and respiratory symptoms. In rare causes of mononucleosis, there can be airway compromise due to pharyngeal or tonsillar swelling, cardiac complications, or enlargement of the spleen. Most cases of infectious mononucleosis are caused by infection with the Epstein-Barr virus (EBV), which is a member of the herpes virus family. However other viruses such as cytomegalovirus (CMV), toxoplasmosis gondii infection, adenovirus. In rare cases, acute HIV infections can also mimic infectious mononucleosis.

How is Mononucleosis Diagnosed?

Infectious mononucleosis is usually a clinical diagnosis and based on the symptoms of the athlete. In cases where its unclear if that athlete has mononucleosis, blood tests can be done to look for acute infection due to Epstein-Barr or the presence of heterophile antibodies.

Mononucleosis and Sports Participation

Infectious mononucleosis can limit athletic participation due to the risk of splenic rupture that occurs in a very small number of patients (thought to be less than 0.5% incident). The increased risk of rupture is due to enlargement of the spleen during the infection and typically athletes are held out of contact sports for four weeks after they are diagnosed to reduce the risk of splenic rupture.

Return To Play and Mononucleosis

Updated mononucleosis and sports participation recommendations now allow for light physical activity starting two weeks after diagnosis. It’s also recommended to evaluate the athlete for splenomegaly (enlarged spleen) based on physical exam and ultrasound.

Return To Play With Enlarged Spleen

If there is a normal-sized spleen, physical activity can increase after 21 days post-infection and the athlete can return to full non-contact activity after 28 days (4 weeks). If the athlete has an enlarged spleen at 21 days, its recommended to recheck the size of the spleen at 28 days. If the spleen has returned to normal size, then the athlete can be released to full sports-participation. In cases where the spleen remains mildly enlarged (but unchanged from the initial evaluation) this enlargement may be physiologically normal for the athlete, especially in taller or larger athletes. The recommendation is to discuss with the athlete the risks of splenic rupture with their return to full sports participation. In cases where the follow-up evaluation of the spleen demonstrates a continued enlargement of the spleen, further workup for the splenomegaly is recommended.

Risk of splenic rupture with mononucleosis

There is a small risk (less than 0,5%) of splenic rupture in athletes with infectious mononucleosis due to transient enlargement of the spleen from the viral infection. The concern is that even a small amount of blunt abdominal trauma can cause rupture of the spleen, resulting in a potential surgical emergency. Rupture of the spleen typically presents with moderate to severe left-sided abdominal pain. However, in some cases, splenic rupture may present with more vague complaints such as shoulder or back pain, and can potentially delay treatment as a result.



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