## Recognized Complications of Diphtheria **Key Point:** Diphtheria toxin causes systemic complications primarily through exotoxin-mediated tissue damage, affecting the heart, nervous system, and respiratory tract. Acute tubular necrosis (ATN) secondary to rhabdomyolysis is NOT a recognized complication of diphtheria. ### Cardiac Complications (Most Common) - Myocarditis with arrhythmias, conduction blocks (AV block, bundle branch block) - Cardiogenic shock and sudden cardiac death - Occurs in 10–25% of cases; most common cause of death - Toxin-mediated myocardial necrosis and inflammation ### Neurological Complications - **Cranial nerve involvement:** Palatal paralysis (vagus nerve), recurrent laryngeal nerve palsy → hoarseness - **Peripheral neuropathy:** Descending pattern — cranial nerves first, then limb nerves - **Respiratory muscle paralysis:** Phrenic nerve involvement → respiratory failure requiring mechanical ventilation - Occurs in 5–10% of cases, typically 2–3 weeks after onset ### Why ATN/Rhabdomyolysis Is NOT a Complication - Diphtheria toxin does not directly cause muscle breakdown or myoglobinuria - The systemic manifestations are exotoxin-mediated, not from direct muscle injury - Renal involvement in diphtheria is rare and not secondary to rhabdomyolysis - Acute kidney injury in diphtheria, if it occurs, is from shock (cardiogenic or septic), not from myoglobin precipitation **High-Yield:** The classic triad of diphtheria complications = **Myocarditis + Cranial nerve palsies + Respiratory paralysis**. Rhabdomyolysis and ATN are NOT part of the diphtheria syndrome. **Clinical Pearl:** Respiratory paralysis is a late complication and a leading cause of death in the pre-antitoxin era. Modern management with early antitoxin and supportive care has reduced mortality significantly. [cite:Park 26e Ch 8]
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