Cellulitis is frequently over-diagnosed. Clinical signs need to include more than just redness – other indications of inflammation are required for diagnosis – e.g. tenderness, pain, swelling, lymphangitis. The onset and progression of the disorder is also a good pointer – streptococcal cellulitis has a rapid onset usually with rapid expansion of the erythematous zone. New onset inflammation around a pre-existing leg ulcer that extends more than 1 cm from the edge may also indicate cellulitis (beware contact allergy from dressing materials however).
Erysipelas, infection of the superficial dermis is associated with a sharply demarcated raised border and elevation of the involved skin. Cellulitis is a deeper process involving dermis and subcutaneous fat that causes brawny (less well-demarcated) oedema and a diffuse red border to the involved skin.
Conditions that may masquerade as cellulitis include:
- Stasis dermatitis (also termed ‘venous eczema’) – brown skin pigmentation present from haemosiderin
- Altered vascular dynamics from disordered sympathetic control of vascular tone
- Contact allergy
- Resolved cellulitis – signs of resolution include cessation of the advance, fading redness, diminished oedema, skin peeling
- Other forms of dermatitis
Altered vascular tone
Resolving cellulitis in setting of severe chronic stasis dermatitis