A 7-year-old unvaccinated boy from rural Maharashtra presents with a 3-day history of sore throat, low-grade fever (38.2°C), and progressive difficulty swallowing. On examination, he has a thick, adherent, greyish-white pseudomembrane covering both tonsils and extending into the pharynx. The membrane does not bleed on gentle scraping. His neck is swollen with prominent cervical lymphadenopathy ("bull neck" appearance). He is drooling and has a nasal voice. What is the most likely diagnosis and the immediate management priority?

Explanation

## Clinical Diagnosis: Diphtheria **Key Point:** The clinical triad of adherent greyish-white pseudomembrane, "bull neck" appearance (cervical edema and lymphadenopathy), and unvaccinated status is pathognomonic for diphtheria caused by *Corynebacterium diphtheriae*. ### Diagnostic Features | Feature | Diphtheria | Strep Pharyngitis | Epiglottitis | |---------|-----------|-------------------|-------------| | Membrane | Adherent, greyish-white, extends beyond tonsils | Exudate, easily wiped off | No membrane | | Neck appearance | "Bull neck" (edema + lymphadenopathy) | Mild cervical nodes | Neck stiffness, drooling | | Vaccination status | Unvaccinated | Variable | Variable | | Onset | Gradual (2–3 days) | Acute (1 day) | Acute (hours) | | Systemic toxicity | Marked (fever, malaise) | Mild to moderate | Severe respiratory distress | **High-Yield:** Diphtheria antitoxin (DAT) must be given **immediately** on clinical suspicion — do NOT wait for culture or PCR confirmation. Delay increases risk of myocarditis and neuropathy. ### Management Protocol 1. **Immediate:** Administer diphtheria antitoxin (DAT) IV or IM (20,000–40,000 units depending on severity and duration of illness). 2. **Antibiotic:** Erythromycin 500 mg QID × 7 days (or azithromycin) to eliminate *C. diphtheriae* and prevent transmission. 3. **Supportive:** Airway monitoring, fluid management, cardiac monitoring (risk of myocarditis). 4. **Isolation:** Respiratory isolation until 2 consecutive negative cultures (48 hours apart) after completing antibiotics. 5. **Contacts:** Prophylaxis with erythromycin 500 mg QID × 7 days; revaccination if incomplete. **Clinical Pearl:** Myocarditis (2–3 weeks post-onset) and peripheral neuropathy (cranial nerves III, IV, VI, then motor nerves) are the leading causes of morbidity and mortality in diphtheria. Early antitoxin administration significantly reduces these complications. **Mnemonic — Diphtheria Complications ("CARD-NEURO"):** - **C**ardiac myocarditis (arrhythmia, heart block) - **A**irway obstruction (pseudomembrane, edema) - **R**espiratory failure (if untreated) - **D**eath (if antitoxin delayed) - **N**eurological: cranial nerve palsies (soft palate, pharynx, eye muscles) - **E**xtension: bulbar involvement - **U**pper airway: stridor, dyspnea - **R**ecurrent: reinfection if not vaccinated - **O**culopalatal: palatal paralysis **Warning:** Do NOT wait for culture confirmation or throat swab results. Empirical DAT administration on clinical grounds is standard of care and saves lives. Culture is confirmatory only. [cite:Park 26e Ch 9]