eschar
Summary
An eschar is an area of dead, blackened, adherent tissue forming a firm crust over a wound. The painless black eschar with surrounding non-pitting oedema is the hallmark of cutaneous anthrax.
Detail
Cutaneous anthrax begins as a painless pruritic papule at the site of inoculation, becomes vesicular, then ulcerates and dries into a depressed black necrotic centre surrounded by a ring of vesicles and impressive gelatinous oedema; painlessness is a key feature distinguishing it from staphylococcal or streptococcal infection. It accounts for most anthrax cases and has low mortality with treatment. Eschars occur in several other diagnoses worth grouping: the tache noire of scrub typhus at the site of a chigger bite, which points to Orientia tsutsugamushi in Southeast Asia; rickettsialpox; ecthyma gangrenosum from Pseudomonas aeruginosa bacteraemia in neutropenic patients, which is painful and rapidly progressive; mucormycosis with black necrotic nasal turbinates and palatal eschar in diabetic ketoacidosis; brown recluse spider bites; and full-thickness burns and pressure injuries. Circumferential burn eschar of a limb or the chest can act as a tourniquet and requires escharotomy. Anthrax eschar should not be debrided, as manipulation risks bacteraemia; treatment is antibiotic.
Sources
- Harrison's Principles of Internal Medicine
- First Aid for the USMLE Step 1
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