cellulitis

Introduction

Infection with inflammation of cellular or connective tissue.

Inflammation may be diminished or absent in immunosuppressed individuals.

Etiology

• entry of bacteria through a disruption in the skin
  • laceration
  • puncture wound
  • fungal intertrigo
  • poison oak/ivy
• extension from contiguous focus
  • abscess
  • extension from ethmoid sinuses in orbital cellulitis
• metastatic dissemination from bacteremia
• spread through the lymphatics & blood stream
• predisposing factors
  • prior trauma
  • underlying skin lesion
  • peripheral neuropathy
  • diabetes mellitus
  • venous & lymphatic compromise
    • saphenous venectomy for CABG
    • chronic venous insufficiency
      • pedal edema, lower extremity edema
    • lymphedema
  • arterial insufficiency
  • fungal infection
    • tinea pedis
    • onychomycosis
  • heart failure
• causative organisms
  • group A beta-hemolytic Streptococci (> 73%) (non-purulent)
  • Staphylococcus aureus, including MRSA
  • uncommon causes
    • group B,C,G Streptococcus, Streptococcus pneumoniae
    • immunocompromised patients
      • Serratia, Proteus, Enterobacter
      • Cryptococcus neoformans
    • persons handling meat, fish, poultry
      • Erysipelothrix rhusiopathiae
      • generally begins on hands
    • Aeromonas hydrophilia
      • contamination of open wound in fresh water or soil
      • contact with medicinal leeches
    • Vibrio species
      • V. vulnificus, V. alginolyticus, V. parahaemolyticus
      • contamination of open wound in salt water or seafood
      • cirrhosis & bullous cellulitis -> V. vulnificus
    • Pasteurella multocida
      • cat scratch or cat bite
    • Capnocytophaga canimorsus
      • contact with dogs, especially patients with asplenia
    • Bacillus anthracis
      • contact with infected animals, bioterrorism
    • Francisella tularensis
      • contact or bite from infected animal (esp cats)
      • tick bite
    • Mycobacterium marinum
      • contact with fresh water or salt water, including swimming pools & fish tanks
• Mycobacterium fortuitum
  • footbaths, pedicures, augmentation mammoplasty, open heart surgery, razor shaving

Pathology

* histopathology images

Clinical manifestations

• acute onset
  • prolonged recovery
    • most patients continue to have symptoms after 10 days of therapy
• presents as well-demarcated erythematous plaque with swelling, warmth, pain, tenderness & spreading erythema
• unilateral when it occurs in the lower leg
• fever/chills, malaise
• lymphadenopathy & lymphatic streaking
• absence of pruritus
• hemorrhagic bullous cellulitis & cirrhosis suggests Vibrio vulnificus
• loss of sensation suggests compartment syndrome due to deep infenction
• purulent drainage, abscesses, furuncles, carbuncles or bullous impetigo in association with cellulitis suggests Staphylococcus aureus
• edema, prurutis, central eschar suggests anthrax
• ulcerative lesion with central eschar, localized lymphadenopathy, constituional symptoms suggest tularemia
• trauma-associated, upper extremity papular lesion becomes ulcerative at site of innoculation, ascending lymphatic spread without systemic symptoms suggests Mycobacterium marinum
• multiple boils suggests Mycobacterium fortuitum

* images

Diagnostic criteria

• no gold standard
• ~40% misdiagnosis

Laboratory

• blood cultures
  • if signs & symptoms of systemic toxicity
  • immunodeficiency, immersion injury, mammal bite
  • generally unrewarding, not cost-effective
• skin-site cultures
  • gram stain & culture from infected site
  • generally not useful
  • skin biopsy with nucleic acid for infectious agent or culture fail to identify a pathogen in most cases
• complete blood count
  • neutropenia suggests ecthyma gangrenosum due to Pseudomonas

Radiology

• computed tomography (CT) or magnetic resonance imaging (MRI)
  • pain out of proportion to erythema
  • rule out myonecrosis, necrotizing fasciitis
• imaging in general not cost-effective

Differential diagnosis

• stasis dermatitis
  • most common misdiagnosis
  • cellulitis can develop in the context of stasis dermatitis
• erysipelas (compare images)
  • superficial infection involving skin, but not soft tissue
  • distinct raised border
  • bright red in color
• tissue necrosis
  • necrotizing fasciitis, myonecrosis, gas gangrene
  • pain/tenderness much greater than degree of erythema would suggest
• deep vein thrombosis with stasis dermatitis
• inflammatory carcinoma of the breast
• cutaneous neoplasm
• pyoderma gangrenosum
• ecthyma gangrenosum (neutropenic patients)
• contact dermatitis is pruritic
• panniculitis, erythema nodosum
  • painful bilateral subcutaneous nodules
• Herpes zoster
  • cellulitis can develop in the context of Herpes zoster
• insect sting
• drug reactions
• eosinophilic cellulitis (the Wells syndrome)
• gouty arthritis, gouty cellulitis
  • tendon involvement is common in patients with tophaceous gout
    • Achilles tendon (52%)
    • peroneal tendon (29%)
• familial Mediterranean fever
• foreign-body reactions
• subsutaneous abscess

* often misdiagnosed in the emergency department

Management

• general measures
  • assess risk of MRSA: risk of MRSA associated with
    • recent hospitalization
    • antibiotic use
    • family history of cellulitis
    • athletic team members
    • prisoners
  • antibiotic treatment should cover Staphylococcus unless etiology is known
  • immobilization & elevation of affected limb initially may be helpful
    • prophylaxis for venous thromboembolism with LMW heparin if patient immobilized for >= 4 days
  • moist heat my serve to localize infection
  • incision & drainage of associated abscesses
  • beta-lactam antibiotics are the drugs of choice
  • outpatient antibiotic treatment (no drainage, abscess)
    • cephalexin (Keflex) 500 mg PO QID
      • addition of Bactrim to cephalexin of no benefit
    • doxycycline or monocycline (MSSA, MRSA) as effective as cephalexin
    • penicillin VK if group A Streptoccoccus most likely
    • dicloxacillin (Dynapen) 500 mg to 1 g PO QID
      • if due to Staphylococcus aureus (MSSA)
    • erythromycin 500 mg QID (for PCN allergy)
    • Bactrim for community-acquired MRSA
      • coverage of group A Streptococci is uncertain
    • Rocephin 1 g IM initially & for 1st few days
    • clindamycin (MSSA, Streptoccocus)
      • treatment of choice for mild, non-purulent cellulitis
      • treatment of MRSA uncertain
      • if systemic symptoms, MRSA coverage indicated
    • linezolid (MRSA)
    • 5 days of therapy as effective as 10-14 days, 7-10 days average
  • inpatient antibiotic treatment (IV)
    • nafcillin (Nafcil, Unipen) 1-2 g IV every 4 hours
    • cefazolin (Ancef) 1-2 g IV every 8 hours
    • MRSA: vancomycin, linezolid or daptomycin
      • vancomycin if systemic symptoms & poor response to dicloxacillin or nafcillin
    • duration of antibiotic therapy:
      • continue until 3 days after disappearance of acute inflammation
      • 7 days of oral antibiotics upon hospital discharge as effective as 14 days in preventing readmission in children
• special considerations
  • lower extremity cellulitis associated with cutaneous ulcers in patients with diabetes mellitus
    • may be polymicrobial in origin
    • agents with anaerobic activity may be indicated
      • metronidazole 500 mg IV every 6 hours, 250-750 mg PO TID
      • clindamycin 600-900 IV every 8 hours, 150-450 mg PO QID
      • linezolid 600 mg IV or PO every 12 hours
      • penicillin 500 mg PO every 8 hours
      • cefoxitin 1-2 g IV every 8 hours
    • add Bactrim or doxycycline for MRSA coverage
    • add fluoroquinolone to enhance gram-negative coverage
  • immunocompromised patients
    • ticarcillin clavulanate (Timentin) 3.1 g IV every 6 hours
    • cefoxitin (Mefoxin) 1 g IV every 6 hours
    • fluoroquinolone if neutropenia
  • orbital cellulitis
    • hospitalization
    • broad spectrum antibiotics
    • surgical drainage if no improvement within 48 hours
  • Erysipelothrix: penicillin
  • Vibrio species
    • aminoglycosides
    • tetracycline f Aeromonas hydrophilia
    • aminoglycosides
    • chloramphenicol
• predictors of treatment failure
  • temperature >38 C at triage (odds ratio, 4.3)
  • chronic leg ulcers (OR, 2.5)
  • chronic edema or lymphedema (OR, 2.5)
    • treatment of venous insufficiency, eczema, & interdigital Tinea can reduce risk of recurrent cellulitis
  • prior cellulitis in the same area (OR, 2.1)
  • cellulitis at a wound site (OR, 1.9)
• surgical consultation
  • signs of toxicity, purple bullae, ecchymoses, sloughing of skin
  • necrotizing fasciitis or myonecrosis on CT or MRI
    • pain out of proportion to erythema
  • cellulitis following recent trauma, surgery or childbirth
  • evidence of compartment syndrome
• follow-up
  • two weeks to ensure eradication of cellulitis
  • tinea infection when present should be treated (including tinea pedis & onychomycosis)
  • prophylactic antibiotics
    • recurrent cellulitis
      • penicillin VK 250-500 mg BID includes elderly with renal insufficiency
      • number need to treat to prevent 1 recurrence = 5
  • compression therapy (fitted compression stockings) reduces recurrence of lower leg cellulitis from 40% to 15%

More general terms

• bacterial infection
• skin infection
• sign/symptom

More specific terms

• erysipelas
• Ludwig's angina; sublingual & submandibular cellulitis
• orbital cellulitis

Additional terms

• gas gangrene (anaerobic cellulitis)