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Infectious Mononucleosis

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Overview

Also known as glandular fever, infectious mononucleosis is a syndrome characterised by severe sore throat, cervical lymphadenopathy, fatigue, fever, and increased mononuclear white cells and other atypical lymphocytes. Around 90% of cases are due to the Epstein-Barr virus (EBV, also known as human herpesvirus 4) and a rarer cause is cytomegalovirus.

Its name originated after a group of students were observed to have pharyngitis, lymphocytosis and atypical monocytes.

Epstein-Barr Virus

Pathophysiology

The Epstein-Barr virus is most commonly transmitted through the saliva, and has the name ‘kissing disease’. EBV tends to infect lymphoid tissue. Upon entering the pharynx, it infects the tonsils and then oropharyngeal B-cells, which then spread the infection and infiltrate the lymphatic system and the liver and spleen. Humoral and cellular immune responses follow with T-cells playing a crucial role in attenuating EBV infection. Heterophile antibodies are produced.

It is thought that an intense immune response is responsible for the symptoms seen and not primary infection as over 90% of people are infected with EBV by the time they are adults.

EBV can also remain latent in infected lymphocytes and alter their genetic expression, resulting in an increased risk of malignancy.

Associations

As well as causing infectious diseases, EBV is associated with:

Epidemiology

  • Infectious mononucleosis is most common in adolescents and young adults
  • Over 90% of people are infected with EBV by the time they are adults

Presentation

Features of infectious mononucleosis include:

  • A triad of fever, sore throat, and lymphadenopathy (>90%) lasting >1 week
    • The lymphadenopathy tends to be cervical but can be generalised
    • Tonsillar erythema and exudates may be seen
    • Palatal petechiae may be seen
  • A maculopapular, pruritic rash if amoxicillin is taken during infection in nearly all patients
    • The reason for this is unknown
  • Splenomegaly (~50%) – this may be prone to rupture
  • Hepatomegaly (~10%) – evidence of hepatitis may be seen

Investigations

Overview

Key investigations include:

  • Full blood count (FBC) – ideally should be done in the 2nd week of illness
    • Shows lymphocytosis and may show atypical lymphocytes
  • Heterophile antibodies (Monospot test) – ideally should be done in the 2nd week of illness:
    • Positive
  • Liver function tests (LFTs):
    • May show transiently elevated transaminases

Management

Overview

Since infectious mononucleosis is generally self-limiting, management is supportive with rest, adequate fluids, simple analgesia, and avoiding alcohol. Patients should also avoid contact sports for 4 weeks due to the risk of splenic rupture.

Complications

  • Splenomegaly and splenic rupture – due to high numbers of infiltrating lymphocytes. Rupture may occur due to trauma (e.g. contact sports) and sometimes lesser impactful activities (e.g. coughing, vomiting, bowel movement) or it may occur spontaneously. This presents acute abdominal pain.
  • Neurological complications – including encephalitis and meningitis
  • Chronic active EBV infection – very rare. Suggested by symptoms persisting >3 months
  • Malignancy – particularly haematological malignancies derived from lymphocytes including Hodgkin’s lymphoma, Burkitt’s lymphoma, gastric cancer, and nasopharyngeal cancer.

Prognosis

  • In most people, infectious mononucleosis is self-limiting and resolves within 2-4 weeks 
  • Fatigue is common and can last from weeks to months

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