The most common locations for cutaneous diphtheria lesions are lower legs and feet; other sites include face, trunk, and hands. The lesions begin as a pustule or vesicle which develops into an ulcer that is initially painful. The ulcers have dark red-purple color with undermined borders and yellow-brown membrane or crust covering its base. Regional lymph nodes are often enlarged. Complications of infection with toxigenic strains include myocarditis (which may lead to arrhythmias) and peripheral neuropathy. Polyneuritis involving multiple cranial nerves may cause diplopia, slurred speech, or dysphagia.
Microscopic examination reveals necrosis in epidermis and dermis. The ulcer base shows necrotic debris, fibrin, and an acute inflammatory infiltrate. Bacteria are difficult to visualize in histologic specimens. The diagnosis can be made by isolating C. diphtheria from the center of the wound. There may be superimposed infection by other bacteria. Treatment consists of penicillin, erythromycin, and use of antitoxin. Diphtheria vaccine is effective but booster doses are recommended every 10 years to maintain immunity.