Review Question - QID 108959

The patient in this vignette presents with fever and pseudomembranous pharyngitis suggestive of diphtheria. Diphtheria toxin inhibits beta-oxidation of fatty acids in the myocardium, leading to eventual myocarditis and cardiomyopathy.

In this patient with a sore throat who is possibly unvaccinated due to recent immigration, the differential diagnosis should include mononucleosis, viral pharyngitis, bacterial pharyngitis, and oropharyngeal candidiasis. The presence of greyish-white pharyngeal pseudomembranous plaques on physical exam is consistent with diphtheria. Diphtheria is caused by infection with Corynebacterium diphtheria, a gram-positive bacillus. It is rarely seen in the USA due to the widespread adoption of the Tetanus-Diphtheria-Pertussis (Tdap) vaccine. Signs of cardiac involvement (e.g., arrhythmias, heart failure) may appear 7-14 days after the pharyngeal symptoms. Diphtheria produces an exotoxin that inhibits ribosome function via ADP ribosylation of elongation factor 2 (EF-2), a protein that is necessary for peptide elongation. This exotoxin acts systemically but shows preference for the myocardium.

Figure A demonstrates the characteristic appearance of pharyngeal pseudomembranous plaques in a patient with diphtheria. These plaques are greyish-white and highly vascular.

Incorrect Answers:
Answer 1: Erythema infectiosum (Fifth disease) is a common viral syndrome caused by parvovirus B19. It presents with a classic “slapped cheek” rash that spreads to the arms, trunk, and then legs. Parvovirus B19 is not associated with pharyngitis.

Answer 2: Mononucleosis is a syndrome characterized by fever, pharyngitis, and splenomegaly. It is caused by Epstein-Barr virus (EBV) and cytomegalovirus (CMV). Patients with mononucleosis are at increased risk of splenic rupture if they sustain trauma due to concurrent splenomegaly. Although mononucleosis should be on the differential diagnosis for this patient, the presence of greyish pseudomembranes in an unvaccinated child is most consistent with diphtheria.

Answer 3: Staphylococcus scalded skin syndrome is a desquamating rash caused by an exotoxin produced by S. aureus. S. aureus rarely causes pharyngitis and is unlikely for the patient in this vignette.

Answer 4: Rheumatic fever is an autoimmune sequela of untreated streptococcal infection. It is caused by cross-reactivity of antibodies between M protein, a virulence factor produced by S. pyogenes, and self-antigens. Although strep pharyngitis should be high on the differential diagnosis in any pediatric patient with fever and pharyngitis, the presence of greyish pseudomembranes in an unvaccinated child is most consistent with diphtheria.

Bullet Summary:
Corynebacterium diphtheriae causes a syndrome characterized by pharyngitis with pseudomembranous plaques followed by myocarditis and peripheral neuropathy. It is only seen in unvaccinated children due to the widespread use of the Tdap vaccine.