• Definition: an ulcerative lesion extending into the dermis that develops in the setting of bacteremia
• Pathogen: Pseudomonas aeruginosa (not pathognomonic but is the most common causative organism)
• Pathophysiology:
  • Classically develops in patients with P. aeruginosa bacteremia who are immunocompromised
  • Bacteria invade vasculature, causing septic vasculitis and cutaneous necrosis
  • Virulence factors destroy tissue:
    • Exotoxin A: inhibits elongation factor 2, impairing protein synthesis
    • Elastase: degrades elastin in blood vessel walls
    • Phospholipase C: breaks down cell membranes
• Clinical features
  • Rapid progression (within 12–18 hours) of painless red macules → induration, development of pustules, vesicles, and/or bullae → crusted ulcers