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Chapter 53: The Mononucleosis Syndromes

DEFINITION

  • Infectious mononucleosis is defined as any blood lymphocytosis induced in response to an infectious agent.

  • Usually greater than 50% of the circulating white cells are lymphocytes, more than 10% of which have the morphology of reactive lymphocytes (Figure 53–1).

  • Table 53–1 lists the etiologic agents that produce mononucleosis.

  • Pharyngeal form:

    — A sore throat is preceded by 1 to 2 weeks of lethargy.

    — Epstein-Barr virus (EBV) generally is the cause.

  • Glandular form without pharyngitis:

    — Lymph node enlargement occurs.

    — The usual cause is an agent other than EBV (eg, Toxoplasma gondii).

  • Typhoidal form:

    — Lethargy with fever or diarrhea without pharyngitis, usually as a consequence of cytomegalovirus (CMV).

FIGURE 53–1

A–D. Blood films from patients with Epstein-Barr virus–induced mononucleosis. These reactive lymphocytes exhibit the characteristic changes seen in patients with infectious mononucleosis: large lymphocytes with abundant cytoplasm. The cytoplasmic margin often spreads around (is indented by) neighboring red cells, and the margin may take on a densely basophilic coloration. This type of reactive T lymphocyte may be seen in a variety of diseases and is not a specific change but is characteristic for Epstein-Barr virus infection. (Reproduced with permission from Lichtman MA, Shafer MS, Felgar RE, et al: Lichtman’s Atlas of Hematology 2016. New York, NY: McGraw Hill; 2017. www.accessmedicine.com.)

Four photomicrographs of stained blood films show the findings in infectious mononucleosis.
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TABLE 53–1 ETIOLOGIC AGENTS ASSOCIATED WITH MONONUCLEOSIS SYNDROME
Epstein-Barr virus Hepatitis A
Cytomegalovirus Adenovirus
Human immunodeficiency virus Toxoplasma gondii
Human herpes virus-6 Bartonella henselae
Metapneumovirus Brucella abortus
Rubella  

ETIOLOGY AND PATHOGENESIS

  • Causes are either of two members of the herpes virus family: EBV or CMV.

  • After the early phase of fever, which lasts for 3 to 7 days, laboratory abnormalities include a blood lymphocyte proportion greater than 50%, often with greater than 10% reactive lymphocytes.

  • Table 53–2 lists other complications of EBV and CMV mononucleosis.

TABLE 53–2COMPLICATIONS IN PATIENTS WITH EBV OR CMV MONONUCLEOSIS
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TABLE 53–2 COMPLICATIONS IN PATIENTS WITH EBV OR CMV MONONUCLEOSIS
  EBV CMV
Hemolytic anemia ++ +
Thrombocytopenia + +
Aplastic anemia + –
Splenic rupture + –
Jaundice (age >25 years) ++ ++
Guillain-Barréa + ++
Encephalitisa ++ +/–
Pneumonitisa +/– +
Myocarditisa + –
B-cell lymphoma + –
Agammaglobulinemia + –

CMV, cytomegalovirus; EBV, Epstein-Barr virus.

aCan occur without mononucleosis syndrome. ++, common; +, infrequent; +/–, uncommon; –, not observed.

FEATURES OF MONONUCLEOSIS CAUSED BY EACH ETIOLOGIC AGENT

  • Table 53–3 list the signs and symptoms associated with EBV and CMV mononucleosis.

  • Target cell for EBV mononucleosis is the B lymphocyte.

  • Target cell for CMV mononucleosis is the macrophage.

  • The “mononucleosis” for both is an increase in reactive ...

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