## Most Common Site of Diphtheria Membrane **Key Point:** The oropharynx and tonsils are the most common sites for pseudomembrane formation in diphtheria, accounting for approximately 90% of cases. ### Anatomical Distribution of Diphtheria | Site | Frequency | Clinical Features | | --- | --- | --- | | **Oropharyngeal (tonsils, soft palate)** | ~90% | Most common; thick, adherent, grayish membrane; "bull neck" appearance | | Nasopharyngeal | ~5% | Serosanguinous discharge; often missed initially | | Laryngeal | ~3% | Croup-like presentation; stridor; respiratory obstruction risk | | Cutaneous | ~2% | Rare; usually in tropical regions; slower toxin production | | Conjunctival/Otitic | <1% | Uncommon; associated with poor hygiene | **High-Yield:** The characteristic "bull neck" appearance (massive cervical edema with lymphadenopathy) occurs in oropharyngeal diphtheria and indicates severe systemic toxemia. **Clinical Pearl:** Nasopharyngeal diphtheria is often missed because the membrane is less visible and serosanguinous discharge may be mistaken for viral rhinitis. Always suspect diphtheria in any unvaccinated child with pharyngeal membrane. ### Why Oropharynx is Most Common 1. **Bacterial tropism** — *Corynebacterium diphtheriae* preferentially colonizes the oropharyngeal mucosa 2. **Membrane adherence** — The oropharyngeal epithelium provides optimal conditions for pseudomembrane formation 3. **Toxin production** — Maximum toxin production occurs at the oropharyngeal site, leading to systemic complications **Warning:** Do not confuse diphtheria membrane with strep throat exudate — diphtheria membrane is thick, adherent, and extends beyond tonsillar borders; removal causes bleeding.
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