Infectious Mononucleosis

Detailed Overview

EBV is a human herpesvirus (HHV-4) transmitted primarily through infected saliva. It infects B lymphocytes and epithelial cells of the oropharynx. The profound immune response, characterized by the proliferation of atypical cytotoxic T cells (CD8+), causes the prominent systemic symptoms. It commonly affects adolescents and young adults.

Epidemiology & Demographics

Peak incidence is between 15 and 24 years of age. By adulthood, over 90% of the worldwide population is seropositive for EBV. Incidence in the US is roughly 500 cases per 100,000 persons per year.

Etiological Mechanism

Epstein-Barr virus (EBV) causes 90% of cases. Cytomegalovirus (CMV), Toxoplasma gondii, and primary HIV infection can cause a 'mononucleosis-like' syndrome.

Primary Causes

Epstein-Barr Virus (EBV)

• Age 15-24: High school and college students are at highest risk for symptomatic primary infection.
• Close contact: Sharing drinks, utensils, or kissing individuals actively shedding the virus.
• Immunocompromised state: Risk for more severe or chronic manifestations.

EBV enters via the oropharynx and binds to the CD21 receptor on B lymphocytes. The virus replicates within these cells and causes a lifelong latent infection. The body mounts a massive cellular immune response, particularly via CD8+ cytotoxic T cells, which appear as 'atypical lymphocytes' on a peripheral smear. This rapid expansion of T cells infiltrates lymphoid tissues, causing massive tonsillar enlargement, generalized lymphadenopathy, and splenomegaly.

Characteristic Clinical Presentation

• Profound Fatigue: Overwhelming exhaustion that can last for weeks or months.
• Severe Sore Throat: Often accompanied by large, pus-covered tonsils making swallowing painful.
• Fever: High fever, peaking in the afternoon or evening, lasting 1-2 weeks.
• Myalgias: Generalized muscle aches and malaise.

Physical Examination Signs

• Posterior cervical lymphadenopathy (highly characteristic)
• Tonsillar exudates (white/grey pseudomembrane) and palatal petechiae
• Splenomegaly (detectable in 50% of patients, peaking in weeks 2-3)
• Hepatomegaly (often with mild jaundice)
• Maculopapular rash (almost universally occurs if mistakenly prescribed Amoxicillin/Ampicillin)

• Splenic Rupture: A rare (0.1-0.5%) but potentially fatal complication occurring usually in the first 3 weeks; often from minor trauma.
• Airway Obstruction: Massive tonsillar hypertrophy can compromise the airway.
• Hematologic derangements: Autoimmune hemolytic anemia or severe thrombocytopenia.

Diagnostic Criteria & Guidelines

Clinical triad of fever, pharyngitis, and lymphadenopathy, confirmed by a positive heterophile antibody test (Monospot) and peripheral smear showing lymphocytosis with >10% atypical lymphocytes.

Differential Diagnosis

• Streptococcal Pharyngitis (Group A Strep)
• Cytomegalovirus (CMV) infection
• Acute HIV infection
• Toxoplasmosis

Laboratory Tests & Biomarkers

• Heterophile Antibody (Monospot): Positive (may be false negative in first week of illness or in young children).
• Complete Blood Count (CBC): Absolute lymphocytosis (>4,500/microL) with >10% atypical lymphocytes.
• Liver Function Tests (AST/ALT): Elevated 2-3 times the upper limit of normal in 90% of cases.
• EBV Specific Antibodies: IgM to Viral Capsid Antigen (VCA-IgM) is positive; EBNA-IgG is negative.

Imaging Modalities & Findings

• Abdominal Ultrasound: Not routine, but used if splenic rupture is suspected or to objectively clear an athlete for contact sports; shows splenomegaly.

• Incubation
  4 to 6 weeks post-exposure.
• Acute Phase
  2 to 4 weeks of acute fever, pharyngitis, and adenopathy.
• Convalescent Phase
  Weeks to months of gradual resolution of fatigue.

Second-Line & Adjunctive Therapy

Corticosteroids (e.g., Dexamethasone 10 mg IV or Prednisone 40 mg PO taper) are strictly reserved for impending airway obstruction, massive splenomegaly, or severe hemolytic anemia.

Surgical & Procedural Management

Emergency splenectomy is required for splenic rupture. Tonsillectomy is rarely needed for recalcitrant airway obstruction.

Recommended Lifestyle Changes

• Absolute avoidance of all contact sports and heavy lifting for at least 3-4 weeks from symptom onset, or until spleen is clinically normal.
• Rest heavily during the acute phase, returning to school/work part-time as tolerated.
• Avoid alcohol consumption to prevent further strain on the liver.

Patient Counseling & Advice

Reassure that prolonged fatigue (up to 3-6 months) is a normal part of the recovery process. Warn about the signs of splenic rupture (sudden, severe left upper quadrant pain radiating to the left shoulder - Kehr's sign).

Follow-Up & Monitoring Schedule

Outpatient follow-up in 1-2 weeks to assess spleen size and airway. Clear for contact sports usually requires a physical exam confirming resolution of splenomegaly at week 4.

Preventive Strategies

No vaccine exists. Avoid sharing drinks, utensils, and kissing when actively ill, though asymptomatic shedding can occur intermittently for life.

Generally excellent with full recovery. Fatigue is the most persistent symptom. EBV remains latent for life and is weakly associated with future risk of Hodgkin lymphoma, Burkitt lymphoma, and Multiple Sclerosis.