Cutaneous diphtheria is caused by Corynebacterium diphtheriae, a pleomorphic, aerobic, Gram-positive bacillus that causes symptoms through the production of a bacteriophage-dependent exotoxin. Human beings are the only known reservoir for Cdiphtheriae, which can only inhabit mucous membranes and skin and is therefore spread by respiratory droplets or contact with the exudate of a diphtheritic cutaneous lesion, including objects contaminated with discharge from the lesion. There are three forms of cutaneous diphtheria:
Primary infection, which begins as a pustule or vesicle on previously normal skin
Superinfection of an eczematized lesion
Secondary infection of a wound
Cutaneous diphtheria typically follows an indolent course, usually remaining local, with few known cases of toxic complications (cardiomyopathy or neuropathy) as seen more frequently with upper respiratory tract diphtheritic infections. However, cutaneous infection is associated with more bacterial shedding and higher rates of transmission of pharyngeal and cutaneous diphtheria to close contacts. The skin is often an importation reservoir for Cdiphtheriae and is associated with sporadic cases of respiratory diphtheria; therefore, prompt recognition and treatment of cutaneous diphtheritic infection may reduce environment contamination with Cdiphtheriae.
Those at greatest risk for cutaneous diphtheria are people living in impoverished, crowded, unhygienic environments, particularly in the developing world, or immigrants from countries where rates of vaccination with diphtheria toxoid are low. Southeast Asia is a known endemic area, and the disease has been associated with the tropics although it exists in temperate regions as well. There has been a shift in the age demographics of cases occurring in the United States; in the pre-vaccination era it was typically a pediatric problem. Now it is more common in those aged over 15, since this population is less likely to have had the vaccination or adequate boosters.
Cutaneous diphtheria often occurs in areas of skin that already have a pathologic process, such as a burn, bite, or eczema. It can also occur as the primary pathologic process, with a predisposition to co-infection with streptococci or Saureus. Hence, it can be very difficult to differentiate diphtheritic skin lesions from other bacterial skin lesions, such as impetigo and ecthyma, without a culture.
It is possible to have simultaneous infections of the pharynx and skin, so any patient with pharyngeal diphtheria should also have cutaneous lesions or wounds cultured, and vice versa. Although unusual, there has been a report of genital cutaneous diphtheria, mimicking donovanosis (granuloma inguinale), syphilis, or ulcerative herpes simplex virus with human immunodeficiency virus (HIV).
The differential of non-genital cutaneous diphtheritic ulcer includes:
