Mononucleosis

Pathophysiology of Mononucleosis

Mononucleosis is an

infection with Epstein-Barr virus (or sometimes CMV with slightly different clinical presentation) in adolescence or early adulthood

Signs and Symptoms

1) prodrome of fatigue, malaise, and myalgias
2) tender but mobile lymphadenopathy (especially in posterior cervical chain)

3) fever
4) exudate pharyngitis
5) splenomegaly
6) splenic rupture (0.5%)
7) mouth petechiae
8) gingivitis
9) abdominal pain
10) rash (10%)
11) symptoms usually resolve in 3-4 weeks

Characteristic Test Findings

Laboratory –

1) leukocytosis with at least 10% lymphocytes
2) presence of Paul-Bunnell heterophile antibody (this is the basis of the diagnostic monospot test)
3) presence of transient cold agglutinins
4) increased AST, ALT, alkaline phosphatase

Histology/Gross Pathology

1) atypical lymphcytes (mostly CD8+ T-cells) with clumped chromatin and irregular nuclei surrounded by RBCs (ballerina-skirt)
2) atypical lymphocytes resemble Reed-Sternberg cells, causing diagnostic confusion
3) infiltration of splenic red pulp (and lymph node sinuses) with atypical lymphocytes
4) EBV is a linear, double-stranded DNA virus
5) CMV intranuclear with “halos”

Associated Conditions

1) splenic rupture (0.5%)
2) bacterial superinfection (10%)
3) autoimmune hemolytic anemia (2%)
4) rash if ampicillin is given (90% of cases not considered a true allergic reaction)
5) fulminant liver failure
6) CNS involvement (ataxia, hemiplegia, psychosis)
7) Guillain-Barre syndrome
8) pneumonia
9) arthritis

Biochemistry

1) virus binds to nasopharyngeal cells and B-lymphocytes, which carry it systemically
2) activated T-lymphocytes kill Ebstein-Barr infected B-lymphocytes

Inheritance/Epidemiology

1) prodrome lasts 4-6 weeks
2) asymptomatic carriers intermittently shed virus
3) person-to-person contact is via infected oral secretions

Treatment

supportive in immunocompetent individuals

Tips for USMLE

1) CMV mononucleosis differs from EBV mononucleosis – CMV etiology usually does not cause pharyngitis or posterior neck lymphadenopathy and does not have Paul-Bunnell heterophile antibodies
2) a heterophile antibody is a human antibody that reacts with the blood cells of another species, such as a sheep or guinea pig
3) if question mentions an 18 year old college freshman who develops a “dragged-out feeling” in the middle of the semester and then develops a headache, sore throat, and enlarged posterior neck lymph nodes during finals, think mononucleosis from EBV.