Eighty percent of people who have infectious mono will have a viral-like syndrome, frequently with sore throat, fever, headache, fatigue, and swollen lymph nodes in the neck. In the belief that they have a cold, many of these people will not seek medical attention and, thus, will have mono that goes undiagnosed. Mono gets a bad rap because of the complications that 20 percent of people may experience. Complications may include such severe swollen glands in the neck that breathing or eating is compromised. Mono can also affect the lining around the brain, producing an encephalitis-like picture.
Mono can inflame the liver, producing a hepatitis.
The spleen can become enlarged. Because of the tight capsule around the spleen, enlargement can produce pain and the danger of rupturing, even with minor trauma. Mono has also been associated with fatigue varying from a few weeks to a few months. Mono gets its bad reputation because people with severe complications of mono get more notoriety. On exam it is impossible to tell mono apart from any number of other viral causes of sore throat, fever, and swollen glands.