Dermatology

Cellulitis: Clinical Presentation, Differential Diagnosis and Treatment

Summary:

Cellulitis is an infection of the soft tissue deep to the skin that results in erythema, inflammation, tenderness, and pain. It is most commonly caused by Streptococcus pyogenes or staphylococcus aureus. Other etiology bacteria include haemophilus influenza, streptococcus pneumonia, gram negative, and anaerobic species. The treatment is with antibiotics targeted at the suspected etiologic organism. Cephalexin is standard for non-purulent cellulitis, with coverage for methicillin-resistant staphylococcus aureus being necessary in the setting of purulence. Duration and intravenous (IV) versus oral anti- microbial therapy is dependent on the clinical severity

Microbiology

Beta-hemolytic streptococcus species
Staphylococcus aureus
- Most common organism in abscesses with the exception or perioral or perirectal locations
- Large burden of methicillin-resistance Staphylococcus aureus (MRSA)
Specific situations
- Pasteurella multocida in the setting of animal bites
- Aeromonas hydrophila and Vibro vulnificus in water exposure
- Clostridium species in gas gangrene

Clinical Presentation

Presents as a local area of erythema(less obvious on hyperpigmented skin tones), warmth, tenderness, and pain
May be patchy
Typically unilateral
Lower extremities are the most common location
Skin should be inspected for areas of breakdown, including maceration
- Other predisposing conditions include lymphedema, venous insufficiency, immunocompromise, tinea infections

Cellulitis of the right thigh. Image courtesy of dermnetnz.org

Cellulitis of the right leg. Image courtesy of dermnetnz.org

Risk Factors & Transmission

Any skin disruption, such as tinea, ulcers, or wounds
Prior cellulitis
Venous insufficiency or impaired lymphatic drainage
Chronic edema
Obesity
Injection drug use

Differential Diagnosis

Erysipelas | Has sharply demarcated and raised borders
Necrotizing fasciitis
Gas gangrene
Varicella zoster
Stasis dermatitis
- Typically both lower legs unlike unilateral presentation in cellulitis
Septic arthritis or bursitis
- Consider if located near a relevant structure
Gout
- Consider if clearly inflamed joint or a prior history of similar symptoms
Insect bite
- Some bites can be associated with large local reactions, e.g., Lyme disease (without typical ‘bullseye’ pattern)
- Outdoor activity or unusual location for cellulitis may point to Lyme

Diagnosis

Clinical diagnosis suspected when there is an appropriate history and physical exam
Identify if any abscess is present either clinically or with ultrasound

Treatment

Incise and drain any detectible abscess
Culture any abscess, although deferral is reasonable in a typical case
- Skin cultures of non-purulent cellulitis are not recommended
Mark the leading edge of erythema

Antibiotic choice depends on location of care and suspected etiologic agent (see below)

Location of care
- Admission is indicated for systemic signs, intractable pain, suspicion of deep space infection, immunocompromise, or failed outpatient treatment
- Admission requires intravenous antibiotics and blood cultures are recommended
- Transition to an appropriate oral agent may occur after clinical improvement
Etiologic agent
- Purulent infections must consider agent active against MRSA
- Perirectal, perioral, or pressure ulcers require MRSA, gram-negative, and anaerobic coverage pending culture results
- If cellulitis associated with penetrating trauma or if evidence of MRSA infection elsewhere, nasal colonization with MRSA, injection drug use, or systemic inflammatory response syndrome; coverage against both MRSA and streptococci recommended
See below for antibiotic choices

Duration

Uncomplicated cellulitis: 5 days of therapy is sufficient if clinical improvement has occurred
Admitted patients: Up to 14 days may be required depending on clinical course

Antibiotics list

Purulent infection, with or without abscess (MRSA coverage needed)

Oral agents
- Trimethoprim-Sulfamethoxazole 1-2 double-strength tablets BID
- Doxycycline 100 mg BID
- Clindamycin 300-450 mg QID
Intravenous agents
- Vancomycin dosed per hospital protocol
- Linezolid 600 mg every 12 hours
- Daptomycin 4 mg/kg every 24 hours

Non-purulent infection (coverage for MRSA considered if risk factors)

Oral agents
- Cephalexin 500 mg QID
- Dicloxacillin 500 mg QID
- Clindamycin 300-450 mg QID
- Trimethoprim-Sulfamethoxazole 1-2 double-strength tablets BID
Intravenous agents
- Cefazolin 1 g every 8 hours
- Nafcillin or oxacillin 1 g every 8 hours
- Clindamycin 600 mg every 8 hours