Diphtheria Signs and Symptoms
Diphtheria presents with the classic triad of sore throat, low-grade fever, and a gray adherent pseudomembrane on the tonsils, pharynx, or nose—remember "Gray Membrane, Sore Throat, Bull Neck" for the key features. 1
Primary Clinical Features
The hallmark presentation includes:
- Sore throat is typically the first symptom and a cardinal feature of respiratory diphtheria 1
- Low-grade fever accompanies the infection, distinguishing it from high-grade fevers seen in other pharyngeal infections 1
- Gray pseudomembrane that is firmly adherent to the mucosa of the nasopharynx, tonsils, pharynx, larynx, or nose—this is the most distinctive diagnostic feature 1, 2
- The membrane has a leathery appearance and bleeds when attempts are made to remove it 3, 4
Pathognomonic Signs
- "Bull neck" appearance results from massive cervical lymphadenopathy and soft tissue edema caused by toxin-mediated vascular damage—this finding is virtually diagnostic 3
- Neck swelling with cervical lymphadenopathy is prominent 5, 4
- Bleeding with swabbing of the pharyngeal membrane distinguishes diphtheria from streptococcal pharyngitis 3
Progressive Respiratory Symptoms
- Hoarseness of voice occurs as the membrane extends to involve the larynx 5
- Inspiratory stridor indicates impending airway obstruction and represents a medical emergency 3
- Extension of the pseudomembrane into the trachea-bronchial tree can cause life-threatening airway compromise 1
- Odynophagia and dysphagia develop as the infection progresses 4
Systemic Complications from Toxin Dissemination
- Myocarditis (toxin-mediated cardiac complications) can develop from systemic absorption of diphtheria toxin 1, 6
- Neuropathy (toxin-mediated neurologic complications) results from toxin dissemination 1, 6
- These systemic effects are associated with increased fatality risk and occur because diphtheria toxin inhibits protein synthesis and causes cell death 6
Easy-to-Remember Mnemonic: "DIPHTHERIA"
- Diphtheric membrane (gray, adherent)
- Inspiratory stridor (airway obstruction)
- Pharyngitis (sore throat—first symptom)
- Hoarseness
- Temperature (low-grade fever)
- Heart complications (myocarditis)
- Edema of neck (bull neck)
- Respiratory obstruction
- Inadequate vaccination (key risk factor)
- Antitoxin needed urgently
Clinical Variants
- Cutaneous diphtheria presents as sharply demarcated skin lesions with a pseudomembranous base, though appearance may not be distinctive 7
- Cutaneous forms are not reportable in the United States but can occur 1
Critical Risk Factor
- Unvaccinated or inadequately vaccinated individuals are at highest risk for severe disease 1, 8
- Most cases occur exclusively in those who are unimmunized or have incomplete immunization 7, 8
Common Pitfall
The key clinical error is failing to consider diphtheria in unimmunized patients with severe pharyngitis, even in industrialized countries where it is rare—the combination of bull neck, inspiratory stridor, and bleeding pseudomembrane should trigger immediate clinical suspicion and urgent antitoxin administration without waiting for laboratory confirmation 3, 9, 5.