Cutaneous Diphtheria Lesion on a Male's Foot

Description

Centered on the distal leg and ankle region, the left foot is presented in a clinical external view with a circumferential erythematous plaque adjacent to the malleolar area and a darker, ulcerated core. The lesion lies superficial to the ankle joint line, within the cutaneous and subcutaneous tissues overlying the distal tibia and fibula, with surrounding skin of the dorsum and lateral foot appearing comparatively uninvolved. Both feet are visible for side-to-side comparison of color and swelling. A gray-white pseudomembranous surface is suggested over the ulcer bed, consistent with toxin-mediated necrosis. Cutaneous diphtheria, caused by toxigenic Corynebacterium diphtheriae, often presents as a chronic, punched-out ulcer with an adherent membrane that bleeds on attempted debridement, and it can be mistaken for ecthyma, infected insect bites, or necrotic cellulitis. Adults with incomplete immunization remain at risk, and the clinical importance is not just local tissue injury but the potential for systemic diphtheria toxin effects, including myocarditis and neuropathy, even when the primary site is skin. Swab culture on selective media with tox gene testing and prompt antitoxin plus erythromycin or penicillin are standard, with contact precautions because cutaneous lesions can be an underrecognized reservoir for transmission. In teaching, this asset fits infectious disease, dermatology, and wound care modules where learners need to recognize pseudomembrane-forming ulcers on the lower extremity and distinguish them from staphylococcal ecthyma, cutaneous anthrax eschar, or vasculitic ulceration. It also suits public health and outbreak communications illustrating how diphtheria can present outside the pharynx, including in vaccinated populations with waning immunity. Anatomical accuracy verified by SciePro's Medical Advisory Board.