Erysipelas

What is it?

Erysipelas represents a distinctive bacterial skin infection affecting the upper dermis and superficial lymphatic vessels, characterized by a raised, intensely red, and sharply demarcated skin lesion. This acute infection, primarily caused by Streptococcus pyogenes bacteria (Group A streptococcus), creates a characteristic "step sign"—an abrupt elevation between infected and normal skin that distinguishes erysipelas from deeper skin infections like cellulitis. The affected area appears shiny, swollen, and fiery-red, often accompanied by systemic symptoms such as fever and chills. Unlike cellulitis, which extends into subcutaneous fat, erysipelas remains confined to the superficial layers, involving prominent lymphatic vessel inflammation that may create visible red streaking. Historically known as "St. Anthony's fire" due to its intense burning sensation and bright red appearance, erysipelas requires prompt antibiotic treatment to prevent complications.

Who is affected?

Erysipelas shows distinct epidemiological patterns across populations:

• Incidence: Approximately 72 per 100,000 person-years, affecting 1% of emergency department visits
• Age distribution: Peak occurrence in patients aged 60-80 years, though all ages can be affected
• Gender: Slightly more common in females (54% female vs 46% male)
• Anatomical preference: Lower extremities (66-80%), upper extremities (14%), face (9%), trunk (8%)
• Risk factors:
  • Lymphedema (strongest predictor, 20-fold increased risk)
  • Obesity (2.3-fold increased risk)
  • Diabetes mellitus
  • Chronic venous insufficiency
  • Athlete's foot (provides entry portal)
  • Previous episodes (22% have recurrent disease)
• Recurrence rates: 7.7% within one year, up to 41% within five years

What causes it?

Erysipelas results from bacterial invasion through compromised skin barriers:

Primary pathogen:

• Streptococcus pyogenes (Group A β-hemolytic streptococcus): Most common cause
• Other streptococci: Group G (S. dysgalactiae), Group C, increasingly recognized
• Entry portals: Skin breaks, surgical incisions, insect bites, fungal infections between toes, chronic ulcers

Pathogenesis:

• Bacterial entry: Organisms penetrate through minor skin trauma
• Lymphatic spread: Rapid invasion through superficial lymphatic vessels
• Inflammatory response: Intense local reaction creates characteristic redness and swelling
• Toxin production: Streptococcal exotoxins contribute to systemic symptoms

Predisposing conditions:

• Local factors: Lymphedema, venous insufficiency, skin barrier disruption
• Systemic factors: Diabetes, obesity, immunosuppression
• Environmental: Poor hygiene, overcrowding, inadequate wound care

What are the clinical features?

Erysipelas presents with pathognomonic (uniquely characteristic) features:

Cardinal signs:

• Raised lesions: Elevated plaques above surrounding skin level
• Sharp demarcation: Clear, well-defined border creating the "step sign"
• Brilliant color: Fiery-red to salmon-red appearance
• Surface texture: Shiny, tense, indurated (firm), with possible "peau d'orange" (orange peel) appearance

Systemic symptoms:

• Fever and chills: Often precede skin changes by 48 hours
• Malaise: General feeling of illness
• Lymphatic involvement: Tender regional lymph nodes (lymphadenopathy)
• Red streaking: Visible lymphangitis extending from affected area

Facial presentation:

• Butterfly distribution: Characteristic pattern across cheeks and nasal bridge
• Sharp margins: Abrupt transition from involved to normal skin
• Higher risk: Potential for serious complications due to proximity to eyes and brain

How is it diagnosed?

Diagnosis relies primarily on clinical recognition, with prompt antibiotic therapy essential:

Diagnosis:

• Clinical diagnosis: Based on characteristic appearance (raised, red, sharply demarcated)
• Laboratory tests: Usually unnecessary; blood cultures positive in minority of cases
• Differential diagnosis: Must distinguish from cellulitis, necrotizing fasciitis, deep vein thrombosis, contact dermatitis
• Warning signs: Severe pain, rapid progression, crepitus suggest necrotizing infection requiring emergency care

First-line treatment:

• Penicillin (gold standard):

  • Oral: Penicillin V 500 mg four times daily
  • Severe cases: IV Penicillin G 2-4 million units every 4-6 hours
  • Duration: 5 days for uncomplicated cases

• Alternatives for penicillin allergy:

  • Cephalexin 500 mg four times daily
  • Azithromycin 500 mg day 1, then 250 mg daily
  • Clindamycin 300-450 mg three times daily

Supportive care:

• Elevation: Raise affected limb to reduce swelling
• Rest and hydration: Essential during acute phase
• Pain control: Acetaminophen or NSAIDs
• Compression: After acute phase for lymphedema management

What is the prognosis?

With appropriate treatment, outcomes are generally excellent:

Treatment response:

• Rapid improvement: Most patients respond within 48-72 hours
• Complete resolution: Typically within 7-10 days with antibiotics
• Excellent prognosis: Full recovery expected with prompt treatment
• Complications: Rare with appropriate therapy (<1% serious complications)

Recurrence prevention:

• Recurrence risk: 18-41% over five years despite treatment
• Prophylactic antibiotics: Reduce recurrence by 69% in frequent cases
• Address risk factors: Treat athlete's foot, manage lymphedema, control diabetes
• Long-term management: May require ongoing preventive antibiotics for recurrent cases

Potential complications (if untreated):

• Local: Abscess formation, chronic lymphedema, skin necrosis
• Systemic: Bacteremia, toxic shock syndrome (rare)
• Long-term: Elephantiasis with repeated episodes
• Mortality: 15% one-year mortality (often related to underlying conditions)

Key points for patients

• Erysipelas is a treatable bacterial skin infection requiring prompt antibiotics
• The characteristic raised, red patch with clear borders helps distinguish it from other infections
• Early treatment prevents complications and speeds recovery
• Recurrence is common—address underlying risk factors
• Seek immediate care for high fever, rapid spread, or severe pain
• Complete the full antibiotic course even if symptoms improve
• Prevention includes good skin care, treating fungal infections, and managing chronic conditions