18. Erysipelas

1. Definition

• Erysipelas → acute infection of the dermis and superficial lymphatics, with a sharply demarcated, raised red plaque
• Cellulitis → deeper infection of the dermis and subcutaneous fat, with ill-defined borders

2. Epidemiology

• Most common site → lower limb (85%); face second
• Elderly, women; recurrence in 20–30%

3. Aetiology and risk factors

• Streptococcus pyogenes (group A beta-haemolytic streptococcus) → most common cause
• Groups B, C, G streptococci; rarely Staphylococcus aureus
• Portal of entry:
  • Tinea pedis (athlete's foot) → interdigital fissures
  • Minor wounds, abrasions, insect bites
  • Leg ulcers, surgical wounds
  • Nasal or ear fissures → facial erysipelas
• Risk factors:
  • Lymphoedema → after mastectomy, radiotherapy, saphenous vein harvest
  • Venous insufficiency
  • Obesity, diabetes
  • Previous erysipelas

4. Pathogenesis

• Streptococci enter the dermis through a break in the skin
• Spread along dermal lymphatics → serous inflammation, oedema
• Toxins and enzymes (streptolysin, hyaluronidase) → spreading margin
• Damage to lymphatics → lymphoedema → further attacks → elephantiasis
• Immune mechanisms → may cause post-streptococcal glomerulonephritis

5. Classification

By local form

1. Erythematous → redness and oedema only; most common
2. Bullous → blisters with serous fluid
3. Haemorrhagic → bleeding into the skin and blisters
4. Phlegmonous → spread into subcutaneous tissue, pus
5. Necrotic (gangrenous) → skin necrosis; elderly, diabetics

By course

• Primary, recurrent (same site), repeated (new site)
• Migratory (wandering) → spreads to new areas while old ones settle

By severity

• Mild, moderate, severe (toxic)

6. Clinical picture

General symptoms

• Sudden onset → high fever 39–40 °C and rigors, often before skin signs
• Headache, malaise, nausea, vomiting
• Confusion in the elderly

Local symptoms

• Bright red, shiny, hot, tense plaque
• Sharp, raised border → irregular, tongue-like or flame-like edges
• Burning pain, tenderness
• Peau d'orange skin from oedema
• Butterfly pattern on the face
• Regional lymphadenitis, lymphangitic streaks
• Healing → peeling of the skin, pigmentation

7. Diagnosis

Laboratory

• Leucocytosis, raised ESR and CRP
• Anti-streptolysin O (ASO) titre → rises after 1–2 weeks
• Blood cultures → positive in < 5%
• Urine → proteinuria, haematuria (glomerulonephritis)

Imaging

• Ultrasound → excludes abscess
• Duplex ultrasound → excludes deep vein thrombosis

8. Differential diagnosis

• Cellulitis
• Deep vein thrombosis → no sharp border, no high fever at onset
• Necrotising fasciitis
• Contact dermatitis → itch, no fever
• Erysipeloid → hands of butchers and fishmongers, Erysipelothrix rhusiopathiae
• Gout, superficial thrombophlebitis
• Herpes zoster

9. Treatment

Conservative

• Penicillin → drug of choice
  • Benzylpenicillin intravenously in severe cases
  • Phenoxymethylpenicillin orally in mild cases
  • 10–14 days
• Penicillin allergy → clarithromycin, clindamycin
• Bed rest, elevation of the limb
• Analgesics, antipyretics
• Treat the portal of entry → antifungals for tinea pedis
• Do not apply compresses or ointments that macerate the skin

Surgical

• Bullous form → open large blisters, sterile dressings
• Phlegmonous form → incision and drainage
• Necrotic form → debridement of dead skin, later skin grafts

Prevention of recurrence

• Treat tinea pedis, skin care
• Compression for lymphoedema and venous disease
• Weight loss
• Prophylactic penicillin → 2 or more attacks per year (benzathine penicillin every 3–4 weeks or oral penicillin)

10. Complications

• Local → abscess, phlegmon, necrosis, thrombophlebitis
• Lymphoedema, elephantiasis
• Sepsis
• Post-streptococcal glomerulonephritis
• Facial erysipelas → cavernous sinus thrombosis, meningitis