A 4-year-old unvaccinated child from Delhi presents with a 2-week history of sore throat, fever, and the development of a thick, adherent grayish-white pseudomembrane over the tonsils and pharynx. Which is the most common site of pseudomembrane formation in diphtheria?

Explanation

## Sites of Pseudomembrane Formation in Diphtheria **Key Point:** The oropharynx, tonsils, and soft palate are the most common sites of pseudomembrane formation in diphtheria, accounting for approximately 90% of cases (faucial diphtheria). ### Classification of Diphtheria by Site | Site | Frequency | Clinical Features | Severity | |------|-----------|-------------------|----------| | **Faucial (oropharynx, tonsils, soft palate)** | ~90% | Thick, adherent gray-white membrane; "bull neck" appearance possible | Moderate to severe | | Laryngeal | ~5–10% | Stridor, hoarseness, respiratory obstruction | High risk of airway compromise | | Nasal | ~2–5% | Serosanguineous discharge, membrane on nasal septum | Mild, often missed | | Cutaneous | Rare | Membrane over skin lesions | Mild | | Conjunctival | Rare | Membrane on conjunctiva | Mild | **High-Yield:** Faucial diphtheria is the most common presentation and has the highest risk of systemic toxin-mediated complications, including myocarditis, neuritis, and airway obstruction. The pseudomembrane is composed of fibrin, necrotic epithelium, and inflammatory cells, and it is **firmly adherent** to the underlying tissue, causing bleeding if forcibly removed [cite:Park 26e Ch 27]. ### Pathogenesis of Pseudomembrane Formation 1. **Corynebacterium diphtheriae** (toxigenic strain) colonizes respiratory mucosa 2. Diphtheria toxin (produced by lysogenic β-phage) → local tissue necrosis and inflammation 3. Fibrinous exudate → pseudomembrane formation 4. Pseudomembrane extends from tonsils to soft palate, pharyngeal wall, and uvula 5. **"Bull neck" appearance:** Severe edema of neck and submandibular tissues (in severe faucial diphtheria) **Clinical Pearl:** The pseudomembrane in faucial diphtheria is characteristically **gray-white, thick, and firmly adherent**. Attempts to remove it result in bleeding. This is in contrast to the white exudate in streptococcal pharyngitis, which is easily wiped off. The child in this vignette has classic faucial diphtheria. ### Complications by Site - **Faucial:** Myocarditis (most common systemic complication), cranial nerve palsies (especially CN X, IX, VII) - **Laryngeal:** Airway obstruction, asphyxia - **Nasal:** Often missed diagnosis, chronic carrier state **Mnemonic:** **FON** — **F**aucial (most common) > **O**ther sites (laryngeal, nasal) > **N**ot usually cutaneous/conjunctival.