A 6-year-old unvaccinated child from rural India presents with a pseudomembrane in the oropharynx, fever, and cervical lymphadenopathy. Culture on Loeffler's serum medium yields a gram-positive bacillus. Which is the most common site of diphtheria in this patient?

Explanation

## Most Common Site of Diphtheria **Key Point:** Oropharyngeal diphtheria accounts for approximately 90% of all cases of diphtheria caused by *Corynebacterium diphtheriae*. ### Epidemiology of Diphtheria Sites | Site | Frequency | Clinical Features | Prognosis | |------|-----------|-------------------|----------| | **Oropharyngeal** | ~90% | Pseudomembrane, bull neck appearance, respiratory obstruction | Most severe; highest mortality | | Laryngeal | ~5% | Croup-like presentation, stridor | High risk of airway obstruction | | Cutaneous | ~3% | Ulcers, minimal systemic toxicity | Mild, good prognosis | | Nasal | ~2% | Unilateral or bilateral nasal discharge | Mild, often chronic | **High-Yield:** The oropharyngeal form is not only the most common but also the most clinically significant because: 1. Largest bacterial load and toxin production 2. Highest risk of airway obstruction ("bull neck" appearance) 3. Greatest risk of systemic complications (myocarditis, neuropathy) 4. Requires immediate airway management and antitoxin therapy **Clinical Pearl:** The pseudomembrane in oropharyngeal diphtheria is adherent, grayish-white, and extends from the tonsils to the pharynx. Attempts to remove it cause bleeding. This is pathognomonic for *C. diphtheriae* toxin-mediated tissue necrosis. **Mnemonic:** **OROPHARYNGEAL DOMINANCE** — Remember that oropharyngeal diphtheria represents the vast majority of cases and carries the highest morbidity and mortality due to airway compromise and systemic toxin effects. [cite:Robbins 10e Ch 19]