A ruptured spleen. The risk of this is greatest in the second or third week of the illness. It can be the first sign of mono in a small number of people. A ruptured spleen requires immediate surgery.
Airway obstruction and difficulty breathing, which may be caused by severely swollen tonsils that block the throat. Corticosteroids may be given to reduce swelling. In severe cases, the tonsils may need to be removed surgically (tonsillectomy).
Cardiac problems, such as irregular heart rhythms, which can occur during the first 3 weeks of mono. These types of problems usually resolve on their own.
While it is not a complication specific to mono, a serious disease known as Reye syndrome can develop if you give aspirin to a person younger than 20 to treat symptoms of mono. Aspirin should not be used to treat symptoms of mono. Other medicines, such as acetaminophen (for example, Tylenol) or ibuprofen (for example, Advil) can help relieve fever and pain caused by mono. Be safe with medicines. Read and follow all instructions on the label.
Even if you have a complication of mono, it is likely that you will recover completely.