Question
Malignant pustule
Answer
Malignant pustule is the older, classical term for cutaneous anthrax, the most common clinical form of anthrax (caused by Bacillus anthracis), acquired through inoculation of spores into broken/abraded skin, typically from contact with infected animals, hides, wool, or animal products.
Clinical evolution: a small, characteristically painless (or minimally painful), pruritic papule at the site of inoculation; over 1–2 days, this evolves through a vesicular stage and then ulcerates, developing a characteristic black, depressed, necrotic eschar surrounded by marked, often extensive, non-pitting oedema — the “malignant” descriptor refers to this striking, out-of-proportion oedema and dark necrotic appearance.
Pathogenesis: local germination of spores, with bacterial multiplication and toxin production (protective antigen, oedema factor, lethal factor) driving the marked local oedema and tissue necrosis.
Laboratory diagnosis: Gram stain and culture (large, Gram-positive, spore-forming, box-car shaped bacilli, non-haemolytic on blood agar, non-motile “Medusa head” colonies); PCR where available.
Treatment: ciprofloxacin or doxycycline; surgical manipulation of the lesion is avoided, as it risks precipitating systemic dissemination. Prognosis is good (<1% mortality) with prompt treatment.