33-07: Diphtheria

ESSENTIALS OF DIAGNOSIS

GENERAL CONSIDERATIONS

Diphtheria is an acute infection caused by Corynebacterium diphtheriae that usually attacks the respiratory tract but may involve any mucous membrane or skin wound. The organism is spread chiefly by respiratory secretions. Exotoxin produced by the organism is responsible for myocarditis and neuropathy.

CLINICAL FINDINGS

A. Symptoms and Signs

Nasal, laryngeal, pharyngeal, and cutaneous forms of diphtheria occur. Nasal infection produces few symptoms other than a nasal discharge. Laryngeal infection may lead to upper airway and bronchial obstruction. In pharyngeal diphtheria, the most common form, a tenacious gray membrane covers the tonsils and pharynx. Mild sore throat, fever, and malaise are followed by toxemia and prostration.

Myocarditis and neuropathy are the most common and most serious complications. Myocarditis causes cardiac arrhythmias, heart block, and heart failure. The neuropathy usually involves the cranial nerves first, producing diplopia, slurred speech, and difficulty in swallowing.

B. Laboratory Findings

The diagnosis is made clinically but can be confirmed by culture of the organism.

DIFFERENTIAL DIAGNOSIS

Diphtheria must be differentiated from streptococcal pharyngitis, infectious mononucleosis, adenovirus or herpes simplex infection, Vincent angina, pharyngitis due to Arcanobacterium haemolyticum, and candidiasis. A presumptive diagnosis of diphtheria should be made on clinical grounds without waiting for laboratory verification, since emergency treatment is needed.

PREVENTION

Active immunization with diphtheria toxoid is part of routine childhood immunization with appropriate booster injections. The immunization schedule for adults is the same as for tetanus (see Table 30–7). Women should receive Tdap with each pregnancy, preferably between 27 and 36 weeks.

Susceptible persons exposed to diphtheria should receive a booster dose of diphtheria toxoid (or a complete series if previously unimmunized), as well as a course of penicillin or erythromycin.

TREATMENT

Removal of membrane by direct laryngoscopy or bronchoscopy may be necessary to prevent or alleviate airway obstruction. Antitoxin, which is prepared from horse serum, must be given in all cases when diphtheria is suspected. For mild early pharyngeal or laryngeal disease, the dose is 20,000–40,000 units; for moderate nasopharyngeal disease, 40,000–60,000 units; for severe, extensive, or late (3 days or more) disease, 80,000–100,000 units. Diphtheria equine antitoxin can be obtained from the CDC.

Either penicillin, 250 mg orally four times daily, or erythromycin, 500 mg orally four times daily, for 14 days is effective therapy, although erythromycin is slightly more effective in eliminating the carrier state. Azithromycin or clarithromycin is probably as effective as erythromycin. The patient should be isolated until ...