The Problem With Mono

October 8, 2019 | Illness

By Dev K. Mishra, M.D.

President, Sideline Sports Doc

Clinical Assistant Professor of Orthopedic Surgery, Stanford University

Key Points:

  • For athletes, the key issue with mononucleosis is the risk of a ruptured spleen if the athlete returns to sports activity too soon
  • Return to sport requires a minimum of 3 to 4 weeks after the start of the illness

Sam Darnold of the New York Jets has been out of action for some time due to mononucleosis. Actually, he’s not out because of mono, he’s out because there is a risk of a ruptured spleen after mono.

Mononucleosis is fairly common in teenagers and young adults. I’d like to present today some quick facts about mono, what happens to the spleen after mono, the risks from a ruptured spleen, and general guidelines for return to sports.

What Is Mononucleosis, Or “Mono”?

 Mononucleosis is a viral illness, usually caused by the Epstein-Barr virus. The classic appearance includes fever, throat inflammation, and enlarged lymph nodes in the neck. You’ll generally feel crummy with fatigue, lack of energy, and headaches. These symptoms usually last around 3 weeks but can stretch out to 8 weeks.

Mono is transmitted through saliva, or even a cough or sneeze. An experienced physician can usually make the diagnosis based on a physical exam. Confirmation can be made through a blood test called a monospot test.

Treatment for mono involves rest, hydration, proper nutrition, and over the counter pain medication such as Tylenol, Advil, or Aleve.

The Problem For Contact And Collision Sports: Risk Of A Ruptured Spleen

The spleen is an internal organ located on the left side of the body towards the back, just above the lower margin of the rib cage. It’s a vital organ that’s part of the immune system. It serves as a filtration source for blood cells and a storage site for infection-fighting white blood cells.

In mono, the spleen becomes enlarged, typically by 4x or 5x. When the spleen is enlarged it extends below the protection of the rib cage and is vulnerable to injury. A hit to the left lower back is the classic mechanism to injure the spleen, but interestingly more than85% of spleen ruptures occur without contact.

If the spleen is injured it can split apart (rupture), which can be a life threatening emergency. It’s estimated that the death rate from a ruptured spleen could be as high as 9%, although with proper emergency care the death rate is substantially lower, closer to 0.1% to 0.5%.  Regardless of what that actual percentage is, if you’re the one with mono you simply don’t want to take a risk that you’ll rupture the spleen.

Lower The Complication Rate By Withholding Collision And Contact Sports For 3-4 Weeks, Minimum

 Because the vast majority of spleen ruptures after mono occur without contact, there’s some controversy about the best way to determine return to play in a contact sport athlete. This recently published paper showed that most spleen ruptures occurred in the first 31 days after the start of mono symptoms.  And this paper outlines a generally accepted return to play progression, with light activity beginning at 21 days after the start of the mono symptoms. The best available evidence is a 3-4 week rest from sports, minimum.

There is no universally accepted method to determine appropriate return to play timelines for athletes in contact and collision sports. The athlete will need to feel back to his/her normal baseline, blood tests will need to normalize, and for elite athletes we will want to see their spleen imaging (CAT scan or ultrasound) show a return to normal size.

The decision requires input from a physician skilled in medical return to play issues in athletes. If you’re an athlete with mono, be sure to follow closely the counsel from your regular physician, and seek specialty input if there are questions about appropriate return to play.

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