Diphtheria is an acute respiratory infectious disease caused by Corynebacterium diphtheriae. The primary pathological changes involve congestion, swelling, necrosis, and fibrinous exudation of the mucosa in the pharynx and larynx, resulting in the formation of a characteristic, adherent grayish-white pseudomembrane. This is accompanied by systemic symptoms caused by the exotoxin produced by Corynebacterium diphtheriae. Transmission mainly occurs through airborne droplets but also through contaminated dust and objects. Diphtheria is more common in autumn, winter, and spring, predominantly affecting children under the age of 10, with the highest incidence occurring in those aged 2 to 5 years. The disease has become rare due to improved living conditions and widespread vaccination.
Pathology
Local Lesions
Local manifestations are characterized by fibrinous inflammation. Corynebacterium diphtheriae proliferates on the mucosal surface, releasing highly toxic exotoxin, which leads to necrosis of epithelial cells, leukocyte infiltration, and fibrinous exudation. The abundant fibrin, leukocytes, necrotic epithelial cells, and bacteria condense to form the distinctive grayish-white pseudomembrane. In pharyngeal diphtheria, the pseudomembrane adheres firmly to the mucosa and is difficult to dislodge, whereas in laryngeal diphtheria, the pseudomembrane is more loosely attached and may be expelled during coughing.
Systemic Lesions
The diphtheria exotoxin can enter the bloodstream, causing complications such as infectious myocarditis, nephritis, peripheral neuritis, or cranial nerve damage.
Clinical Manifestations
The incubation period ranges from 2 to 4 days. Based on severity, diphtheria is classified into mild, moderate, severe, and very severe forms. Clinically, it is often categorized into localized and infectious types.
Pharyngeal Diphtheria
Pharyngeal diphtheria is the most common form, accounting for approximately 80% of cases.
Localized Type
Symptoms develop gradually. General symptoms include fever, fatigue, and loss of appetite, while local symptoms are mild and may include slight throat pain. Grayish-white pseudomembranes are visible on the tonsils and may extend beyond the palatal arches to cover the soft palate, uvula, or posterior pharyngeal wall. The pseudomembrane adheres tightly to the tissue and is not easily wiped away; forced removal results in a bleeding surface. Smears or cultures of the pseudomembrane typically reveal Corynebacterium diphtheriae.
Infectious Type
Symptoms have an acute onset and progress rapidly. The pseudomembrane quickly expands along with systemic infection symptoms such as high fever, restlessness, rapid breathing, pallor, cyanosis on the lips, cold extremities, a thready pulse, decreased blood pressure, and arrhythmia. Significant swelling of the pharyngeal mucosa, tonsils, uvula, and palatal arches can occur. Enlarged cervical lymph nodes and edema of the soft tissue can cause the neck to swell, creating a "bull neck" appearance.
Laryngeal Diphtheria
Laryngeal diphtheria accounts for 20% of cases and often arises as a downward extension of pharyngeal diphtheria, although primary laryngeal involvement is occasionally reported. Symptoms develop gradually, with a dry, barking cough and hoarseness. Inspiratory dyspnea and stridor may occur when laryngeal mucosa swells or the pseudomembrane blocks the glottis. Severe cases can present with suprasternal, intercostal, and epigastric retractions, cyanosis, and potentially fatal asphyxia. The infection may extend downward to involve the trachea and bronchi, causing lower airway obstruction. Respiratory obstruction is a common cause of death in laryngeal diphtheria.
Nasal and Otic Diphtheria
These forms are extremely rare.
Complications
Infectious Myocarditis
This is common in infectious diphtheria and can lead to death due to heart failure and severe arrhythmias.
Neurological Paralysis
Palatal muscle paralysis is the most frequently observed, followed by paralysis of the ocular and facial muscles. Paralysis of limb muscles may also occur.
Secondary Infections
Secondary infections such as pneumonia, otitis media, lymphadenitis, and septicemia are often caused by streptococci or Staphylococcus aureus.
Diagnosis
The diagnosis is established based on medical history, symptoms, and physical findings, in combination with bacteriological testing. Bacteriological tests include smear microscopy of secretions, immunofluorescence tests, and bacterial cultures. An intradermal Schick test and immunochromatographic assays may assist in diagnosis when necessary.
Treatment
General Management
Strict isolation, bed rest, and a diet consisting of easily digestible and nutritious foods are advised. Oral and nasal hygiene care is necessary.
Pathogen-Specific Treatment
Diphtheria Antitoxin (DAT)
The dosage depends on disease severity and the extent of the pseudomembrane. Dosages typically range from 20,000 to 40,000 units, while severe cases may require 60,000 to 100,000 units. Repeated administration may be necessary in some cases.
Antibiotics
Antibiotics are used to eliminate Corynebacterium diphtheriae and prevent secondary infection. Penicillin is the drug of choice, while erythromycin is suitable for patients allergic to penicillin.
Management of Complications
Patients with myocarditis require absolute bed rest and consultation with relevant specialists. Tracheostomy is indicated for those with respiratory distress or laryngeal obstruction, followed by enhanced postoperative care to prevent pulmonary infections.