Cutaneous diphtheria

Introduction (1)

Corynebacterium diphtheriae is an aerobic, Gram-positive bacillus that produces diphtheria toxin, leading to respiratory or cutaneous disease. Cutaneous diphtheria may also be caused by C. ulcerans, an emerging zoonotic pathogen that is not reliably prevented by vaccination.

Cutaneous diphtheria represents the primary extrapharyngeal manifestations and is often imported via travel from endemic regions.

Epidemiology and transmission (1)

Toxigenic C. diphtheriae is not endemic in the United States, with sporadic cases linked to international travel or exposure to respiratory secretions or skin lesions of infected close contacts. Recent U.S. isolates have predominantly been nontoxigenic.

Incubation period for cutaneous diphtheria ranges from 2–5 days (10 days maximum), shorter than respiratory diphtheria.

Transmission occurs person-to-person, primarily through direct contact with infected cutaneous ulcers or exudates.

Clinical features (1)

Cutaneous diphtheria manifests as a slow-healing, superficial ulcer or multiple ulcers on the lower extremities, hands, or occasionally the trunk.

Primary vesicles or pustules erode to form shallow ulcers (1–3 cm in diameter) with sharply demarcated, irregular “punched-out” borders and characteristic overhanging edges of elevated violaceous edematous granulation tissue. Occasional satellite vesicopustules or bullae may be present.

The ulcer base displays a persistent, adherent, leathery brown-gray or yellowish pseudomembrane composed of fibrin and necrotic debris that bleeds easily on debridement. Regional lymphadenopathy produces tender, enlarged inguinal or axillary nodes.

Complications and sequelae

Systemic toxigenic spread is rare (1–2% of cutaneous cases), manifesting as distant pseudomembranous lesions or toxin-mediated effects including polyneuritis (palate / pharyngeal paralysis), myocarditis, or osteomyelitis. (4)

Concurrent respiratory diphtheria is rare because cutaneous diphtheria is associated with a rapid antibody response, inducing systemic immunity. (4)

Testing and diagnosis

• Perform urgent wound swab for bacterial culture from the ulcer base prior to antibiotic treatment.

• Notify public health officials immediately for contact tracing regardless of culture results.

Patient management and treatment

• Initiate antibiotics such as erythromycin for 14 days.

  • Diphtheria antitoxin is generally not required for localized cutaneous diphtheria.

• Implement contact isolation until two consecutive negative cultures are obtained post-antibiotics (typically after 48 hours of treatment).

Prevention

Routine childhood immunization with DTaP (dosed at 2, 4, 6, 15–18 months, and 4–6 years) followed by Tdap booster at 11–12 years is recommended. (5)