Differential Diagnosis for Purple Swelling after Soft Tissue Infection

• Single Most Likely Diagnosis
  • Erysipelas: This is a type of skin infection that can cause purple swelling, typically on the legs or face. It's caused by streptococcal bacteria and is known for its distinctive appearance and acute onset.
• Other Likely Diagnoses
  • Cellulitis: A common bacterial skin infection that can cause redness, swelling, and warmth of the skin. While it's more commonly red, it can appear purple in some cases, especially if there's significant bruising or if the infection is deep.
  • Abscess: A collection of pus that has built up within the tissue of the body, indicating a local infection. An abscess can cause swelling and may appear purple if it's close to the skin surface and there's significant inflammation or bruising.
• Do Not Miss Diagnoses
  • Necrotizing Fasciitis: A severe infection that destroys the tissue under the skin, including fat and the tissue covering the muscles (fascia). It's a medical emergency and can cause purple swelling due to the death of skin and underlying tissues.
  • Gas Gangrene: Caused by Clostridium perfringens, this condition leads to the death of body tissue (gangrene) and can produce gas under the skin, leading to swelling and discoloration, including purple coloration.
• Rare Diagnoses
  • Purpura Fulminans: A rare, life-threatening condition usually seen in children that is characterized by the rapid progression of hemorrhagic necrosis of the skin, leading to purple discoloration. It can be associated with severe infections.
  • Vasculitis: Inflammation of the blood vessels, which can cause a variety of symptoms including purple discoloration of the skin due to the damage to blood vessels. It's less commonly associated directly with soft tissue infections but can be a consideration in complex cases.