Notes and photos from dermnet –

What is erysipelas?

Erysipelas is a superficial form of cellulitis, a potentially serious bacterial infection affecting the skin.
Erysipelas affects the upper dermis and extends into the superficial cutaneous lymphatics. It is also known as St Anthony’s fire due to the intense rash associated with it.
Unlike cellulitis, almost all erysipelas is caused by Group A beta haemolytic streptococci (Streptococcus pyogenes). 
Staphylococcus aureus, including methicillin-resistant strains (MRSA), Streptococcus pneumoniae, Klebsiella pneumoniae, Yersinia enterocolitica, and Haemophilus influenzae have also been found rarely to cause erysipelas.
Clinical Features – 
      • The affected skin has a very sharp, raised border.
      • It is bright red, firm and swollen. It may be finely dimpled (like an orange skin).
      • It may be blistered, and in severe cases may become necrotic.
      • Bleeding into the skin may cause purpura.
      • Cellulitis does not usually exhibit such marked swelling but shares other features with erysipelas, such as pain and increased warmth of affected skin.
      • In infants, it often occurs in the umbilicus or diaper/napkin region.
      • Bullous erysipelas can be due to streptococcal infection or co-infection with Staphylococcus aureus (including MRSA).
Diagnosis – 
Erysipelas is usually diagnosed by the characteristic rashThe differential of erysipelas is similar to the cellulitis mimics. There is often a history of a relevant injury. Tests may reveal:
Raised white cell count
Raised C-reactive protein
Positive blood culture identifying the organism
MRI and CT are undertaken in case of deep infection
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