Assessment of cellulitis and erysipelas

Cellulitis and erysipelas present as diffuse, spreading areas of skin erythema. Lymphangitis, lymphadenopathy, fever or other systemic features may be present.

Erysipelas is a superficial infection of the upper dermis; the affected area is raised, with a clear line of demarcation between infected and noninfected tissue. It classically involves the facial skin in a butterfly pattern, but also commonly affects a lower limb.

Cellulitis is an infection extending further into the dermis than erysipelas and involves subcutaneous tissue. It can complicate wounds (eg cuts, abrasions), insect bites, chickenpox (varicella), shingles (herpes zoster) and scabies. Cellulitis in children is often periorbital (preseptal); see Assessment of periorbital (preseptal) and orbital (postseptal) cellulitis.

Note: Many conditions present similarly to cellulitis – always consider differential diagnoses.

Accurate diagnosis can be difficult; if uncertain, consider early consultation by a dermatologist or infectious diseases physicianJain, 2017 Li, 2018. Conditions that can be misdiagnosed as cellulitis include:

acute contact dermatitis
arthroplasty device infection
septic bursitis
gout
acute lipodermatosclerosis (commonly occurring in people with obesity and people with venous insufficiency). For more information see The Australasian College of Dermatologists website.

Bilateral lower limb erysipelas and cellulitis are rare; always consider alternative diagnoses.

Note: Bilateral lower limb erysipelas and cellulitis are rare; always consider differential diagnoses.

Evaluate patients with cellulitis for a drainable source of infection (such as an abscess). If a drainable source is identified, collect a sample for culture and susceptibility testing. It can be difficult to determine if there is an underlying abscess if significant overlying induration is present; soft tissue ultrasonography can aid diagnosis and should be considered, if available.

Consider the location and size of the affected area; closer monitoring and a lower threshold for referral and escalation of therapy are required for patients with(NICE), 2019:

involvement of deep structures, such as muscle, bones, joints or fascia, because surgical intervention may be required
cellulitis of the hand
cellulitis of the neck
cellulitis of the face, particularly if located near the eyes or the nose (eg within the triangle from the corners of the mouth to the bridge of the nose) because there is a risk of intracranial extension
a large affected area.

In patients with cellulitis associated with systemic features, assess for necrotising fasciitis or myonecrosis, streptococcal toxic shock syndrome and staphylococcal toxic shock syndrome.