Infectious mononucleosis: Clinical sciences

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Introduction0:00–0:52

Infectious mononucleosis, or mono for short, is a viral illness primarily caused by human herpes virus-4, otherwise known as Ebstein Barr Virus, or EBV.
The virus spreads through close personal contact, usually through saliva or respiratory secretions. Classically, this happens by sharing food or drinks, or by kissing, which is why mono is sometimes called the “kissing disease” and why it’s common in young adults.
Once the virus reaches the new person’s mouth, it infects both epithelial cells and B cells in the oropharynx. It is then carried throughout the body, allowing it to infect other lymphoid tissues including the liver, spleen, and lymph nodes.
Now, if a patient presents with a chief concern suggesting infectious mononucleosis, your first step is to obtain a focused history and physical exam.

History & Physical examination0:52–1:59

Your patient might report fever, fatigue, myalgia, sore throat, and in some cases, nausea, and vomiting. On the other hand, physical exam typically reveals posterior cervical lymphadenopathy, palatal petechia, tonsillar exudates, and possibly splenomegaly.
Here’s a clinical pearl to keep in mind! Splenomegaly in infectious mononucleosis is a result of lymphocytic infiltration in the spleen.
Some patients might note vague abdominal discomfort or referred pain of the left shoulder, while others might be completely asymptomatic.
During physical examination, be sure to check for an enlarged spleen. Palpate below the left costal margin and feel for the splenic edge then percuss for dullness in the lowest intercostal space along the left axillary line.

Suspect Infectious Mononucleosis1:59–3:34

At this point, suspect infectious mononucleosis and obtain a heterophile antibody test, also known as a monospot test. If the heterophile antibody test is positive, diagnose infectious mononucleosis.
Here’s the catch! A false negative heterophile antibody test is common in the early course of the illness.
So, if the test is negative but you still clinically suspect infectious mononucleosis, order a CBC with differential. You can consider getting a peripheral smear to look at the morphology of the blood cells as well.
If the CBC reveals an absolute lymphocyte count greater than or equal to 4000 per cubic millimeter or an elevated lymphocyte count of 50% or more; or the peripheral smear shows at least 10% atypical lymphocytes, you should get a viral capsid IgM test.
If this test is positive, diagnose infectious mononucleosis. If it’s negative, consider an alternative diagnosis.
Now, let’s go back to CBC results. If it shows an absolute lymphocyte count less than 4000 per cubic millimeter, an elevated lymphocyte count less than 50%; and a peripheral smear with less than 10% atypical lymphocytes, consider an alternative diagnosis.
Now that we’ve diagnosed infectious mononucleosis, let’s talk about treatment. Remember, infectious mononucleosis is caused by EBV.

Treatment3:34–4:50

Like many other viral illnesses, treatment includes supportive care with rest and adequate hydration; antipyretics like acetaminophen; and anti-inflammatory medication such as NSAIDs.
You should also instruct your patient to avoid strenuous exercise and contact sports for at least three weeks, due to the risk of splenic rupture.
Here’s one more clinical pearl! Besides splenic rupture, other complications of infectious mononucleosis can occur for weeks, months, or even years after the initial infection, especially in those with weakened immune systems or those taking immunosuppressive medications.
Complications include prolonged extreme fatigue, hepatitis, hemolytic anemia, and thrombocytopenia. Additionally, keep in mind that EBV is associated with an increased risk of developing certain cancers such as Burkitt lymphoma, Hodgkin lymphoma, and nasopharyngeal cancer.
Alright, as a quick recap... Infectious mononucleosis is a viral illness primarily caused by EBV that spreads through close contact via saliva.

Review4:50–5:39

Once you suspect infectious mononucleosis, obtain a heterophile antibody test to confirm the diagnosis. If the test is negative, but you still clinically suspect infectious mononucleosis, you’ll need to get a CBC, peripheral smear, and possibly viral capsid IgM testing.
Treatment includes supportive care with rest and adequate hydration, antipyretics like acetaminophen, and anti-inflammatory medications like NSAIDs.
Also, counsel your patient about the risk of complications such as splenic