## Diphtheria: Diagnosis and Emergency Management **Key Point:** Diphtheria is a clinical diagnosis. Treatment with antitoxin and antibiotics must begin IMMEDIATELY on clinical suspicion—do NOT wait for culture confirmation, as delay increases mortality and morbidity. ### Clinical Diagnosis of Diphtheria This child presents with the pathognomonic triad: | Feature | Significance | |---------|-------------| | **Pseudomembrane** | Thick, grayish-white, adherent, bleeds on removal; hallmark of diphtheria | | **Bull neck** | Cervical edema + lymphadenopathy; indicates severe systemic toxin absorption | | **Sore throat + low-grade fever** | Mild systemic symptoms; toxemia dominates the clinical picture | **High-Yield:** The pseudomembrane in diphtheria is composed of fibrin, dead epithelial cells, and bacteria—NOT pus. This distinguishes it from streptococcal pharyngitis (exudate) or viral pharyngitis. ### Pathophysiology & Why Immediate Treatment Is Critical Diphtheria toxin (produced by lysogenized *Corynebacterium diphtheriae*) causes: 1. **Local tissue necrosis** → pseudomembrane formation 2. **Systemic toxemia** → myocarditis, neuropathy, respiratory paralysis 3. **Airway obstruction** → stridor, respiratory failure Toxin-mediated complications develop over **3–7 days**. Early antitoxin administration neutralizes circulating toxin and prevents irreversible end-organ damage (myocarditis, cranial nerve palsies). ### Immediate Management Algorithm ```mermaid flowchart TD A[Clinical suspicion of diphtheria]:::outcome --> B{Pseudomembrane + systemic signs?}:::decision B -->|Yes| C[Admit to ICU]:::action C --> D[Administer diphtheria antitoxin IV immediately]:::urgent D --> E[Start IV penicillin G 50,000 U/kg/day]:::action E --> F[Isolate respiratory droplets]:::action F --> G[Culture on Loeffler's medium]:::action G --> H[Supportive care: airway management, cardiac monitoring]:::action B -->|No| I[Consider differential diagnosis]:::outcome ``` **Clinical Pearl:** Antitoxin is a horse serum product and carries risk of serum sickness. However, the benefit of preventing toxin-mediated complications far outweighs this risk. Skin testing for hypersensitivity should be performed, but treatment should NOT be delayed. ### Antibiotic Regimen | Drug | Dose | Duration | Notes | |------|------|----------|-------| | **Penicillin G (IV)** | 50,000 U/kg/day in 4 divided doses | 7–10 days | First-line; achieves high tissue levels | | **Erythromycin (if PCN allergy)** | 40–50 mg/kg/day in 4 divided doses | 7–10 days | Alternative; also used for contacts | | **Cephalosporin** | Not recommended | — | Poor CNS penetration; not effective | **Mnemonic:** **DIPHTHERIA MANAGEMENT = DAP** - **D**iphtheria antitoxin (immediately) - **A**ntibiotics (IV penicillin G) - **P**rotective isolation (respiratory droplets for 2–3 days after antibiotics start) ### Why Delay Is Dangerous Antitoxin efficacy decreases with time: - Given within 24 hrs: ~90% effective - Given after 3 days: ~50% effective - Given after 7 days: minimal benefit Myocarditis (the leading cause of death) is irreversible once toxin has bound to cardiac myocytes. Early antitoxin is the only way to prevent this. ### Post-Treatment Considerations 1. **Vaccination:** After recovery, give diphtheria toxoid (as part of Td/Tdap) because infection does not always confer immunity. 2. **Contact prophylaxis:** Close contacts receive erythromycin 40–50 mg/kg/day × 7 days + diphtheria toxoid if not fully vaccinated. 3. **Monitoring:** Watch for myocarditis (arrhythmias, heart failure), neuropathy (cranial nerve palsies, respiratory paralysis), and airway obstruction. [cite:Park 26e Ch 8; Harrison 21e Ch 139]
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