A 63-year-old woman presented with what she thought was a brown recluse spider bite received 10 days earlier. After noticing a small, painless, nonpruritic, red bump on her upper back, she surmised that a spider had bitten her, although she did not see a spider at the time. The following day she applied a “black salve” she had learned about in a local traditional medicines class. A black eschar soon developed, and the lesion became progressively pruritic.
Her medical history was remarkable for a basal cell carcinoma, excised from a separate location on her back seven years ago, and for well-controlled psoriasis. The physical examination revealed a 1-cm concentric black eschar surrounded by a 2-mm fissure and a 4-mm ring of erythema (see accompanying figure) on her upper back.
The answer is D: a reaction to black salve. Black salve is an escharotic compound typically containing bloodroot (Sanguinaria canadensis). Traditionally, it is used by Native Americans as an orange dye and herbal medicine. It was first described in the 1800s as a topical salve used to treat breast cancer and other solid tumors.1 Although recent laboratory studies suggest potential future applications, no clinical data currently support its use for cancer treatment.2 However, it has been used in the past as part of the Mohs surgical technique as a chemical fixative before the procedure.2,3
Approximately 80 percent of reported “spider bites” are caused by nonarachnid sources.7 The tissue necrosis visible in the accompanying figure could be consistent with a brown recluse spider bite; however, the clinical history and onset of symptoms are not. The typical brown recluse bite is painful and associated with development of a lesion within 10 minutes. Infarction at the site presents as a sinking blue macule; surrounding erythema develops two to eight hours later. Forty percent of these bites result in central necrosis, and 20 percent develop severe necrosis.8
Cutaneous anthrax develops as a result of Bacillus anthracis spores entering the body through mucous membranes or breaks in the skin. Average rates in the United States were less than one case per year before the 2001 outbreak. Cutaneous anthrax typically occurs on the arms, face, and neck. A pruritic papule develops within one week of infection and progresses to a 1- to 2-cm vesicle surrounded by nonpitting edema. Rupture and necrosis then occur, followed by a black eschar.
Ecthyma, a type of impetigo, typically begins with discrete vesicles. It is followed by erosion, ulceration, and finally an asymmetrically shaped eschar. This process results from dermal extension of the infection, causing a vasculitis.
Basal cell carcinoma is a malignant tumor of the skin originating from basal cells of the epidermis. It typically begins as a smooth, pink to red nodule with pearly borders. Ulceration and crusting occur with enlargement. This occurs over a longer period than described in this case.
|Brown recluse spider bite||Painful bite and lesion within 10 minutes; sinking blue macule with surrounding erythema develops later; central necrosis in 40 percent of bites|
|Cutaneous anthrax||Pruritic papule develops within one week of infection; evolves into 1- to 2-cm vesicle surrounded by nonpitting edema; rupture and necrosis occur; black eschar follows|
|Ecthyma||Begins with discrete vesicles, followed by erosion, ulceration, and finally an irregularly shaped eschar|
|Reaction to “black salve”||Immediate symmetric necrosis after application of salve|
|Basal cell carcinoma||Smooth, pink to red nodule with pearly borders; ulceration and crusting occur with enlargement|