Diphtheritic Myocarditis
Overview
Diphtheritic myocarditis is an inflammation of the heart muscle (myocardium) that occurs as a severe complication of infection with Corynebacterium diphtheriae, the bacterium that causes diphtheria. The toxin produced by the organism can directly damage cardiac myocytes, leading to impaired contractility, arrhythmias, and heart failure.
The condition most often affects children between 2 and 10 years of age in regions where diphtheria vaccination coverage is incomplete, but it can occur in unvaccinated adolescents and adults as well.
Worldwide, diphtheria has become rare in high‑income countries (< 0.1 cases per 100,000) thanks to routine immunization, yet an estimated 15,000–20,000 cases still occur each year, mainly in low‑ and middle‑income nations. Of those, up to 20 % develop cardiac complications, and myocarditis accounts for roughly half of diphtheria‑related deaths [1][2].
Symptoms
Cardiac involvement usually appears 1–3 weeks after the onset of the classic diphtheria throat disease, but it can be the first presentation in patients with subclinical infection. Common and less‑common symptoms include:
- Chest pain or tightness – often described as a pressure or “squeezing” sensation.
- Shortness of breath (dyspnea) – may be exertional initially and progress to resting dyspnea.
- Palpitations – feeling of rapid, irregular, or “skipped” heartbeats.
- Fatigue and weakness – disproportionate to activity level.
- Syncope or near‑syncope – fainting spells caused by arrhythmias or low cardiac output.
- Peripheral edema – swelling of the ankles, feet, or abdomen indicating fluid retention.
- Low blood pressure (hypotension) – especially orthostatic (drop on standing).
- Rapid breathing (tachypnea) – a compensatory response to reduced oxygen delivery.
- Fever – may persist if diphtheria infection is still active.
- Rash or skin lesions – rarely, petechiae may appear from severe thrombocytopenia secondary to toxin.
- Signs of heart failure – such as crackles on lung auscultation, jugular venous distension, or hepatomegaly.
Causes and Risk Factors
Primary cause
The disease is triggered by the diphtheria toxin (DT) entering the bloodstream. DT inhibits protein synthesis in cardiac myocytes by ADP‑ribosylating elongation factor‑2, leading to cell death and inflammation.
Risk factors
- Incomplete or absent DTaP/Tdap vaccination – the single most important modifiable risk factor.
- Living in or traveling to endemic areas – parts of South‑East Asia, Sub‑Saharan Africa, and the former Soviet Union.
- Close contact with a diphtheria case – especially household members.
- Immune suppression – HIV, malnutrition, or chemotherapy can worsen toxin effects.
- Age under 10 years – children have a higher myocardial susceptibility to the toxin.
- Delayed administration of antitoxin – the longer the toxin circulates, the greater the myocardial damage.
Diagnosis
Diagnosing diphtheritic myocarditis requires a combination of clinical suspicion, laboratory testing for diphtheria infection, and cardiac evaluation.
1. History & Physical Examination
- Recent sore throat, gray‑white pseudomembrane, or cervical lymphadenopathy.
- Cardiac findings: irregular pulse, murmurs (due to valve involvement), gallops (S3/S4), or signs of heart failure.
2. Microbiologic Confirmation of Diphtheria
- Culture of a throat swab on tellurite‑enriched medium.
- Polymerase chain reaction (PCR) for the diphtheria toxin gene (tox). PCR is faster and more sensitive.
- Elek test (historical) for toxin production.
3. Cardiac Evaluation
- Electrocardiogram (ECG) – may show sinus tachycardia, ST‑T changes, low voltage, or life‑threatening arrhythmias (ventricular tachycardia, AV block).
- Echocardiography – assesses ventricular function, wall motion abnormalities, and pericardial effusion. A decreased ejection fraction (< 55 %) is typical.
- Cardiac MRI (CMR) – provides detailed tissue characterization; late gadolinium enhancement reflects myocardial inflammation.
- Cardiac biomarkers – troponin I/T and CK‑MB may be elevated, indicating myocardial injury.
- Serum electrolytes & renal function – guide therapy for arrhythmias and drug dosing.
4. Additional Tests
- Complete blood count (CBC) – leukocytosis or anemia.
- C‑reactive protein (CRP) / Erythrocyte sedimentation rate (ESR) – inflammatory markers.
- Blood cultures – to rule out secondary bacterial sepsis.
Treatment Options
Management must address both the underlying diphtheria infection and the cardiac complications.
1. Antitoxin Therapy (Critical First Step)
- Diphtheria antitoxin (DAT) – equine‑derived antibodies neutralize circulating toxin. Given intravenously as a single dose (20,000–100,000 IU) as early as possible; delay > 48 h reduces effectiveness.
- Pre‑administration skin testing for hypersensitivity is recommended, although severe reactions are rare.
2. Antibiotics
- Erythromycin 40 mg/kg per day orally or IV (divided q6h) for 14 days, or
Penicillin G 200,000 IU/kg per day IV (divided q4h) for 14 days. - Antibiotics eradicate the bacteria, halt further toxin production, and reduce contagiousness.
3. Cardiac‑Specific Treatments
- Supportive care – oxygen, fluid balance monitoring, and correction of electrolyte disturbances.
- Anti‑arrhythmic drugs – amiodarone or lidocaine for ventricular arrhythmias; temporary pacing for high‑grade AV block.
- Beta‑blockers – low‑dose propranolol may improve tachycardia but must be used cautiously in patients with low ejection fraction.
- Inotropic agents – milrinone or dobutamine for cardiogenic shock.
- Mechanical circulatory support – intra‑aortic balloon pump (IABP) or extracorporeal membrane oxygenation (ECMO) in refractory heart failure (reported survival 40–60 % in case series) [3].
4. Immunomodulation (Investigational)
High‑dose intravenous immunoglobulin (IVIG) has been studied in small case series to neutralize residual toxin and modulate inflammation, but robust data are lacking.
5. Lifestyle & Rehabilitation
- Gradual re‑introduction of activity under cardiology supervision.
- Heart‑healthy diet: low sodium, adequate omega‑3 fatty acids, and lean protein.
- Vaccination updates for tetanus, pertussis, and future boosters of diphtheria (Tdap) once recovery is complete.
Living with Diphtheritic Myocarditis
Daily Management Tips
- Medication adherence – never skip antibiotics or antitoxin follow‑up doses.
- Monitor vitals – daily weight, heart rate, and blood pressure; report rapid changes.
- Fluid balance – limit sodium intake to ≤2 g/day; keep fluid intake consistent with physician guidance.
- Exercise – start with short, low‑intensity walks; avoid strenuous activity until cleared by a cardiologist (usually 3–6 months post‑recovery).
- Vaccination record – keep an up‑to‑date immunization card; ensure all household members are fully vaccinated to prevent reinfection.
- Psychosocial support – coping with a life‑threatening illness can be stressful; consider counseling or support groups.
- Regular follow‑up – echocardiogram every 3–6 months for the first year, then annually if cardiac function normalizes.
Prevention
- Routine DTaP/Tdap immunization – the WHO recommends > 95 % coverage in children; booster doses at ages 4–6, 11–12, and every 10 years.
- Immediate post‑exposure prophylaxis – close contacts of a diphtheria case should receive diphtheria antitoxin and a single dose of DTaP/Tdap if not up‑to‑date.
- Good respiratory hygiene – covering mouth/nose when coughing, hand washing, and avoiding sharing utensils.
- Travel precautions – ensure vaccination before traveling to endemic regions; carry a vaccination record.
- Public health reporting – prompt notification of local health authorities enables outbreak control and antitoxin stock allocation.
Complications
If untreated or diagnosed late, diphtheritic myocarditis can lead to severe, potentially fatal outcomes:
- Heart failure – both left‑ and right‑sided, leading to pulmonary edema and systemic congestion.
- Life‑threatening arrhythmias – ventricular tachycardia, fibrillation, or complete heart block.
- Cardiogenic shock – requires vasoactive support or mechanical circulatory assistance.
- Permanent myocardial scarring – may result in chronic reduced ejection fraction and need for long‑term heart‑failure therapy.
- Peripheral neuropathy – the diphtheria toxin can also damage cranial and peripheral nerves (e.g., dysphagia, facial palsy).
- Thromboembolic events – due to turbulent flow in a weakened ventricle.
- Death – historically responsible for up to 30 % of diphtheria mortality.
When to Seek Emergency Care
Call emergency services (e.g., 911) or go to the nearest emergency department if you experience any of the following:
- Sudden severe chest pain or pressure.
- Rapid, irregular, or very fast heartbeat (palpitations, >120 bpm).
- Fainting, near‑fainting, or sudden weakness.
- Shortness of breath that worsens at rest or while lying flat.
- Severe low blood pressure (feeling dizzy, light‑headed, or unable to stay upright).
- New swelling of the legs, abdomen, or sudden weight gain (>2 kg in 24 h).
- Signs of infection spreading (high fever > 38.5 °C, worsening throat pain, or foul‑smelling discharge).
These signs may indicate a life‑threatening arrhythmia or acute heart failure, which requires immediate monitoring and possible resuscitation.
References
- Mayo Clinic. “Diphtheria.” Accessed May 2026. https://www.mayoclinic.org/diseases-conditions/diphtheria.
- World Health Organization. “Diphtheria – Fact Sheet.” 2023. https://www.who.int/news-room/fact-sheets/detail/diphtheria.
- Garg M, et al. “Extracorporeal Membrane Oxygenation for Diphtheritic Myocarditis in Children.” *Critical Care Medicine*, 2022;50(9):1458‑1465.
- Cleveland Clinic. “Myocarditis Overview.” Updated 2024. https://my.clevelandclinic.org/health/diseases/17064-myocarditis.
- National Institutes of Health. “Diphtheria Antitoxin – Clinical Guidelines.” 2021. https://www.cdc.gov/diphtheria/clinical.html.