## Diagnosis and Management: Diphtheria ### Clinical Presentation **Key Point:** The clinical diagnosis of diphtheria is **presumptive and does NOT require culture confirmation before starting antitoxin**. Delay in antitoxin administration increases morbidity and mortality. This child presents with the classic triad: 1. **Pseudomembrane** — gray-white, adherent, extends beyond tonsils 2. **Sore throat and dysphagia** — from local inflammation 3. **'Bull neck' appearance** — cervical edema and lymphadenopathy from toxin-mediated inflammation ### Pathophysiology of Diphtheria Toxin *Corynebacterium diphtheriae* produces **diphtheria toxin** (via lysogenic phage) that: - **Inhibits protein synthesis** by inactivating elongation factor-2 (EF-2) - Causes **local tissue necrosis** → pseudomembrane formation - Causes **systemic toxemia** → myocarditis, neuropathy, respiratory paralysis **High-Yield:** The toxin is absorbed systemically within **24–48 hours**. Antitoxin must be given early to neutralize circulating toxin before it binds to tissues. ### Why Antitoxin Must Be Given Immediately | Timing of Antitoxin | Mortality Rate | |---------------------|----------------| | Day 1–2 of illness | 5–10% | | Day 3–4 of illness | 15–20% | | Day 5–6 of illness | 25–30% | | Day 7+ of illness | >40% | **Clinical Pearl:** Antitoxin efficacy depends on **early administration**. Once toxin binds to tissues, antitoxin cannot reverse the damage. Culture results take 24–48 hours; waiting is dangerous. ### Immediate Management Algorithm ```mermaid flowchart TD A[Clinical suspicion of diphtheria]:::outcome --> B{Pseudomembrane present?}:::decision B -->|Yes| C[Administer DAT immediately]:::action B -->|No| D[Continue supportive care, await culture] C --> E[Obtain throat culture on Loeffler's medium]:::action E --> F[Start penicillin G IV or erythromycin]:::action F --> G[Monitor for myocarditis, neuropathy, airway obstruction]:::action G --> H{Culture confirms C. diphtheriae?}:::decision H -->|Yes| I[Continue antitoxin + antibiotics, supportive care]:::action H -->|No| J[Reassess diagnosis, continue supportive care]:::outcome ``` **Mnemonic: DAT-PENICILLIN** — **D**iphtheria **A**ntitoxin **T**herapy (immediate), then **P**enicillin (or **E**rythromycin), **N**ursing care, **I**solation, **C**ulture, **I**ntubation standby, **L**aryngeal obstruction watch, **L**ate neuropathy monitoring, **I**mmunization after recovery, **N**otification ### Antitoxin Administration - **Source:** Diphtheria antitoxin (DAT) is a horse serum product - **Dose:** 20,000–100,000 units IV (depending on severity and duration of illness) - **Route:** IV preferred for systemic disease; IM for mild cases - **Timing:** **STAT** — do not wait for culture - **Precautions:** Test for horse serum hypersensitivity (anaphylaxis risk ~7–10%) ### Antibiotic Therapy - **Penicillin G** 50,000 units/kg/day IV in divided doses for 7–10 days - **OR Erythromycin** 40–50 mg/kg/day for 7 days (eradicates carrier state) - Eradication of organism confirmed by 2 consecutive negative cultures 2 weeks apart ### Supportive Care - **Airway management:** Intubation only if respiratory obstruction develops (not prophylactic) - **Cardiac monitoring:** Watch for myocarditis (arrhythmias, heart block) - **Neurological monitoring:** Cranial nerve palsies (palate, larynx) and peripheral neuropathy (weeks 2–3) - **Isolation:** Until 2 consecutive negative cultures **Warning:** Do NOT give antitoxin prophylactically to asymptomatic contacts — it is only therapeutic. Contacts should receive **erythromycin prophylaxis** and **booster vaccination**. ### Post-Recovery Immunization - Diphtheria toxoid does NOT develop immunity after natural infection (only 50% of cases) - **Immunize after recovery** with diphtheria-containing vaccine (DPT/Td) [cite:Park 26e Ch 8; Harrison 21e Ch 142]
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