A patient presents with a gray, adherent pseudomembrane on the oropharynx; what is the diagnosis and what medications should be given?

Diagnosis and Treatment of Gray Pharyngeal Pseudomembrane

The diagnosis is respiratory diphtheria caused by toxigenic Corynebacterium diphtheriae (or rarely C. ulcerans), and immediate treatment requires diphtheria antitoxin plus antibiotics (penicillin or erythromycin) without waiting for culture confirmation. 1

Clinical Diagnosis

Respiratory diphtheria presents with a characteristic grayish, adherent pseudomembrane in the pharynx, palate, or nasal mucosa that can obstruct the airway. 1 The pseudomembrane is firmly adherent and distinguishes diphtheria from other pharyngeal infections. 2, 3

Key diagnostic features to assess:

• Gray, adherent membrane that bleeds when removal is attempted 1
• Location: tonsillar zones, soft palate, uvula, pharynx, or larynx 2
• Airway patency: the membrane can cause obstruction 1
• Systemic toxicity: fever, malaise, tachycardia from toxin-mediated cardiac and neurologic complications 1

Immediate Management Algorithm

Step 1: Secure the Airway

• Assess for airway compromise immediately - the pseudomembrane can cause life-threatening obstruction 1
• Prepare for intubation or tracheostomy if respiratory distress is present 1

Step 2: Administer Diphtheria Antitoxin URGENTLY

• Give diphtheria antitoxin as soon as clinical diagnosis is made, without waiting for laboratory confirmation 1
• Antitoxin neutralizes circulating toxin but cannot reverse toxin already bound to tissues 1
• Delay in antitoxin administration increases risk of cardiac and neurologic complications 1

Step 3: Start Antibiotics Immediately

Antibiotic options (choose one): 1

• Penicillin G: 100,000-150,000 units/kg/day IV in divided doses
• Erythromycin: 40-50 mg/kg/day (maximum 2g/day) orally or IV in divided doses

Antibiotics eradicate the organism and stop toxin production but do NOT substitute for antitoxin. 1

Step 4: Obtain Cultures and Notify Public Health

• Collect throat swab for culture on Loeffler or tellurite media before antibiotics if possible, but do not delay treatment 1, 4
• Real-time PCR can detect the toxin gene (tox) more rapidly than culture 4
• Immediately notify public health authorities - diphtheria is a reportable disease requiring contact tracing and prophylaxis of close contacts 1

Critical Pitfalls to Avoid

Do not wait for culture confirmation to start treatment - respiratory diphtheria is a clinical diagnosis requiring immediate antitoxin and antibiotics. 1 Culture confirmation takes days, and delayed antitoxin administration significantly increases morbidity and mortality from cardiac and neurologic complications. 1

Do not confuse with other causes of pharyngeal membranes:

• Streptococcal pharyngitis produces exudate, not adherent pseudomembrane 1
• Infectious mononucleosis causes tonsillar exudate that is easily removed 1
• Candidiasis produces white plaques that scrape off easily (unlike diphtheria's adherent gray membrane) 5

C. ulcerans can also produce toxigenic diphtheria with identical pseudomembrane formation and requires the same urgent treatment approach. 1, 6 This organism is often transmitted from animals (dogs, cattle). 6

Monitoring for Complications

Toxin-mediated complications include: 1

• Myocarditis: monitor ECG for conduction abnormalities (occurs in 10-25% of cases)
• Neurologic complications: cranial nerve palsies (especially velopharyngeal paralysis), peripheral neuropathy, diaphragmatic paralysis 6
• These complications can occur weeks after initial infection despite appropriate treatment 1, 6

Vaccination Status Considerations

Even vaccinated individuals can develop diphtheria if immunity has waned, though disease is typically milder. 1 Serosurvey data shows immunity declines with age, with only 30% of adults >60 years having protective antibody levels. 1 This emphasizes that clinical suspicion should remain high regardless of vaccination history when a gray pharyngeal pseudomembrane is present.