Erysipelas

Relatively common bacterial infection of the upper dermis (usually group A Strep) causing a well-demarcated, raised, intensely red rash (classically on the face or lower leg).

• High-yield example of a superficial cellulitis that spreads rapidly but responds well to antibiotics. Important to recognize and distinguish from deeper infections (cellulitis, necrotizing fasciitis) to prevent severe complications.

• Acute onset of fever, chills, and a painful, bright red area on the skin that is raised with a sharply demarcated border; often on the lower leg (in patients with edema/oedema or lymphatic impairment) or the face.
• The rash is warm, shiny, and swollen; it may show streaking redness along lymphatics and tender regional lymph nodes (reflecting superficial lymphatic spread).
• Common in older adults or infants with predisposing factors (e.g., lymphedema, chronic leg ulcers, tinea pedis fissures, or immunocompromise). Facial cases often follow a recent streptococcal throat infection.

1. Erysipelas vs cellulitis: Erysipelas involves the upper dermis with well-defined, elevated margins and faster onset; cellulitis extends deeper (fat) with ill-defined borders and more gradual spread.
2. Watch for necrotizing fasciitis: pain out of proportion, hemorrhagic bullae, skin anesthesia, rapid extension beyond marked borders, or gas/crepitus suggest deeper infection requiring surgical evaluation.
3. If a joint is involved (erythema overlying a joint) with severe pain on motion, consider septic arthritis rather than just a soft tissue infection.

1. Start antibiotics against Streptococcus promptly: oral penicillin V or amoxicillin for mild cases (5–10 days); if penicillin-allergic, use clindamycin or a macrolide. Use IV penicillin G or cefazolin for severe cases or facial erysipelas with systemic symptoms.
2. Add MRSA coverage (e.g., trimethoprim-sulfamethoxazole, doxycycline, or vancomycin) if risk factors for MRSA are present or initial therapy fails. Supportive care includes limb elevation, hydration, and analgesics/antipyretics for pain and fever.
3. Criteria for hospitalization: severe infection or signs of sepsis, concern for necrotizing fasciitis, immunocompromised status, very young or elderly patients, or lack of reliable outpatient follow-up.

• Mnemonic: Erysipelas has Elevated, Edge-defined rash; Cellulitis has Common (ill-defined) edges and Creeping spread.
• Historical alias "St. Anthony's Fire" recalls the intense red "fiery" appearance of erysipelas.

• Rapid spread beyond marked borders, development of violaceous (purple) skin discoloration or bullae, or decreased sensation in the area → red flags for necrotizing fasciitis (requires emergent surgical intervention).
• Periorbital erysipelas with eye pain or limited extraocular motion → worry about orbital cellulitis (needs urgent evaluation and IV antibiotics to prevent vision loss).

1. Suspect erysipelas from exam (acute well-demarcated rash + fever) → mark the border and begin empiric penicillin (or appropriate antibiotic) for Streptococcus.
2. Monitor closely: if rash spreads rapidly beyond marked border or pain is disproportionate, get urgent surgical consult to rule out necrotizing fasciitis.
3. If typical course: continue 5 days of antibiotics (extend to 7–10 days if slow response). Ensure risk factors are addressed (e.g., treat tinea pedis, use compression for edema).
4. No improvement or atypical features → broaden evaluation: consider adding MRSA coverage, check for alternative diagnoses (e.g., ultrasound to exclude DVT, or evaluate for abscess).

• Elderly diabetic patient with sudden fever and a bright red, shiny, tender plaque on the lower leg with a raised, sharp border → Erysipelas (streptococcal infection of superficial dermis, often via toe web fissures).
• Middle-aged adult with an intensely red, well-demarcated rash on one cheek and fever after a recent sore throat → facial erysipelas (can mimic a lupus malar rash early on).