A 7-year-old unvaccinated child from rural India presents with a pseudomembrane in the pharynx, fever, and cervical lymphadenopathy. Culture on Loeffler's medium yields gram-positive bacilli that ferment glucose but not maltose. Which is the most common site of diphtheria in this patient?

Explanation

## Most Common Site of Diphtheria ### Clinical Presentation The case describes classic pharyngeal diphtheria with pseudomembrane formation, fever, and cervical lymphadenopathy ("bull neck" appearance). ### Site Distribution | Site | Frequency | Clinical Features | Severity | |------|-----------|-------------------|----------| | **Pharyngeal** | 90% | Pseudomembrane, dysphagia, cervical edema | Most common, moderate-to-severe | | Laryngeal | 5–10% | Stridor, airway obstruction | High risk of asphyxia | | Cutaneous | 2–5% | Localized ulcer or erosion | Mild, rarely fatal | | Nasal | <1% | Serosanguineous discharge | Mild, often missed | ### Key Point: **Pharyngeal diphtheria is the most common form, accounting for ~90% of all diphtheria cases.** It presents with a characteristic gray-white pseudomembrane that adheres firmly to the pharyngeal mucosa and does not wipe off easily. ### High-Yield: The pseudomembrane in pharyngeal diphtheria is composed of fibrin, dead epithelial cells, and inflammatory exudate. It extends from the tonsil to the soft palate and uvula, and removal causes bleeding. ### Clinical Pearl: Cervical lymphadenopathy with soft tissue edema creates the "bull neck" appearance, which is pathognomonic for severe pharyngeal diphtheria and indicates systemic toxin absorption. ### Mnemonic: **PDL** — Pharyngeal (90%) > Laryngeal (5–10%) > Localized/Cutaneous (2–5%) [cite:Textbook of Microbiology Baveja 6e Ch 22]