Diphtheria can occur at any age, but 70% occur in children under 15 years old and have not been vaccinated. Myocarditis is one of the particularly serious complications of diphtheria.
Diphtheritic myocarditis occurs in 10%–20% of cases of respiratory diphtheria.
Diphtheria is an acute, epidemic infectious disease, mainly transmitted through the respiratory tract, caused by diphtheria bacilli (Corynebacterium diphtheriae).
The source of diphtheria is infected patients or healthy people who carry the bacteria but do not show symptoms of the disease. The disease is mainly transmitted through the respiratory tract when in contact with droplets from an infected person when coughing or sneezing. In addition, the disease can be transmitted indirectly when in contact with objects contaminated with nasal secretions from an infected person. The disease can also be transmitted through contact with skin lesions caused by diphtheria.
Clinical symptoms usually begin 2-5 days after infection of the nasopharynx and may include sore throat, malaise, cough, hoarseness, painful swallowing, bloody nasal discharge, and salivation. Fever is usually mild or absent. The lesions are characterized by a grayish-white membrane that initially covers the tonsils and then rapidly spreads to the uvula, soft palate, and posterior pharyngeal wall.
In severe cases, the damage causes airway obstruction, respiratory failure. Systemic damage occurs when diphtheria toxin spreads into the bloodstream, leading to toxin-mediated damage to the heart, kidneys, and peripheral nerves.
Doctor Hoang Cong Minh, National Heart Institute, Bach Mai Hospital said that diphtheria exotoxins secreted affect the heart, causing arrhythmia and sudden death due to heart failure. Complications of myocarditis often occur when the patient is in the acute stage or a few weeks after recovery. In cases where myocarditis appears in the early days of the disease, the patient has a poor prognosis and a high mortality rate.
Cardiac complications are common and well documented in diphtheria because diphtheria toxin has a high affinity for myocardial cells and the cardiac conduction system. Myocarditis occurs due to degeneration of actin myofibers caused by diphtheria toxin, leading to impaired myocardial contractility. In patients who recover from the disease, damaged myocardial cells are replaced by fibrotic tissue, which can leave long-term cardiac sequelae.
Cardiovascular manifestations in diphtheria are very diverse but the most typical are myocardial contractility dysfunction and arrhythmia, sometimes with pericarditis and endocarditis.
Diphtheritic myocarditis occurs in 10%–20% of cases of respiratory diphtheria, although the actual number may be higher. Notably, this complication occurs almost exclusively in unvaccinated or incompletely vaccinated individuals.
Myocarditis usually presents late in the second week but may present earlier in severe infections. Diphtheritic myocarditis has a case fatality rate of 60%–70%.
Today, modern monitoring and diagnostic methods, such as invasive blood pressure monitoring, continuous electrocardiographic monitoring, and echocardiography, can help diagnose and manage and detect cardiac dysfunction and arrhythmias early.
Treatment of myocarditis
Currently, diphtheria myocarditis is mainly treated with support to maintain normal hemodynamic parameters. Antiarrhythmic drugs are usually only used for rapid and sustained arrhythmias.
Dr. Minh said that prophylactic treatment of arrhythmias is not recommended. Temporary pacemaker placement may be used in patients with severe diphtheria myocarditis and bradyarrhythmias. The success of temporary pacing depends on the extent of conduction system damage and myocardial reserve.
Treatment of diphtheria includes early use of diphtheria antitoxin and antibiotics. Daily mortality increases with delay in diphtheria antitoxin, from 4.2% in the first two days to 24% by the fifth day of illness.
Antitoxin is considered the cornerstone in preventing severe complications and must be readily available. In Vietnam, only a few level 3 hospitals have diphtheria antitoxin available for early treatment.
"Myocarditis is the most serious complication of diphtheria and the most common cause of death. Although this is considered a life-threatening condition, if anti-diphtheria serum is used promptly and active supportive care is provided, the disease can be successfully treated," emphasized Dr. Hoang Cong Minh.
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