A painless skin ulcer with a black center (eschar) is characteristic of which infection?

A painless skin ulcer with a black center (eschar) is characteristic of which infection?

• A. Erysipelas
• B. Impetigo
• C. Basal cell carcinoma
• D. Cutaneous anthrax

Answer: (D)

The key idea is recognizing the distinctive skin lesion of cutaneous anthrax. Bacillus anthracis infection typically starts as a painless papule that expands and sometimes becomes vesicular, eventually forming a necrotic, black eschar surrounded by edema. The painless progression helps differentiate it from other infections, where pain or warmth is more common. Other choices don’t fit this lesion: erysipelas usually presents as a hot, raised, sharply demarcated red plaque with tenderness and systemic symptoms; impetigo features honey-colored crusts on the skin rather than a black necrotic center; basal cell carcinoma is a chronic, noninfectious skin cancer with a pearly papule and telangiectasias, not an acute painless necrotic ulcer. Therefore, the painless skin ulcer with a black center is most characteristic of cutaneous anthrax.

The key idea is recognizing the distinctive skin lesion of cutaneous anthrax. Bacillus anthracis infection typically starts as a painless papule that expands and sometimes becomes vesicular, eventually forming a necrotic, black eschar surrounded by edema. The painless progression helps differentiate it from other infections, where pain or warmth is more common.

Other choices don’t fit this lesion: erysipelas usually presents as a hot, raised, sharply demarcated red plaque with tenderness and systemic symptoms; impetigo features honey-colored crusts on the skin rather than a black necrotic center; basal cell carcinoma is a chronic, noninfectious skin cancer with a pearly papule and telangiectasias, not an acute painless necrotic ulcer.

Therefore, the painless skin ulcer with a black center is most characteristic of cutaneous anthrax.