A lesion begins as a pruritic papule. The papule enlarges and develops into an ulcer surrounded by vesicles, which usually occurs within 1-2 days. A characteristic black necrotic eschar appears with associated edema and surrounding erythema. After 1-2 weeks, the eschar dries, falls off, and leaves a permanent scar. Associated regional lymphadenopathy and lymphadenitis may be present.
Anthrax is caused by direct skin inoculation by B anthracis .
Physician accuracy with the visual diagnosis of anthrax is poor because of a lack of prior experience with this disease. Histologic findings include massive edema of the upper dermis with attenuation of the overlying epidermis. The deep dermis and subcutaneous fat may show hemorrhage, fibrin deposition, dense infiltrate of lymphocytes, histiocytes, and neutrophils with abscess formation. Antibiotics may delay or eliminate the spread and dissemination of lesions but are ineffective in preventing the progression of a single lesion. Surgical debridement of the necrotic eschar may be necessary in functionally impaired areas.