Topic Overview

Most people recover from mononucleosis (mono) without any complications. But there are many possible complications of mono. These include:^{1, 2, 3}

• An enlarged spleen, which occurs in up to 50 out of 100 people who have mono.
• Red spots or rash, which can develop if you are taking certain antibiotics. The rash is not an allergic reaction.
• Mild anemia, which usually goes away without treatment after 1 to 2 months.
• A lower-than-normal number of platelets in the blood (thrombocytopenia). This condition usually goes away without treatment.
• A lower-than-normal number of neutrophils, a type of white blood cell that helps fight infection. This condition usually goes away without treatment.
• Hepatitis, which can occur most often during the 2nd to 4th weeks of mono.

Other complications of mono can occur but are very rare. These include:

• 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).
• Brain and spinal cord problems.
• 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. Follow all instructions on the label.

Even if you have a complication of mono, it is likely that you will recover completely.