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For further information, see CMDT PART 6-33: INFECTIOUS ERYTHEMAS

Key Features

Essentials of Diagnosis

  • Edematous, expanding, erythematous, warm plaque with or without vesicles or bullae

  • Lower leg is frequently involved

  • Pain, chills, and fever are commonly present

  • Septicemia may develop

General Considerations

  • Usually due to gram-positive cocci, though gram-negative rods or even fungi can produce similar picture

  • The major portal of entry for lower leg cellulitis is toe web tinea pedis with fissuring of the skin at this site

  • Erysipelas is a superficial form of cellulitis that occurs classically on the cheek, caused by β-hemolytic streptococci (see Erysipelas)

Clinical Findings

Symptoms and Signs

  • Cellulitis begins as a tender small patch

  • Swelling, erythema, and pain are often present

  • The lesion expands over hours, so that from onset to presentation is usually 6–36 hours

  • As the lesion grows, the patient becomes more ill with progressive chills, fever, and malaise

  • Lymphangitis and lymphadenopathy are often present

  • If septicemia develops, hypotension may develop, followed by shock

Differential Diagnosis

  • Deep venous thrombosis

  • Venous stasis

  • Candidiasis

  • Anthrax

  • Contact dermatitis

  • Herpes zoster (shingles)

  • Scarlet fever

  • Angioedema

  • Necrotizing fasciitis

  • Sclerosing panniculitis

  • Underlying osteomyelitis

  • Systemic lupus erythematosus

  • Erysipeloid


Laboratory Tests

  • Leukocytosis or at least a neutrophilia (left shift) may be present

  • Blood cultures are positive in only 4% of patients

  • If a central ulceration, pustule, or abscess is present, culture may be of value

  • Aspiration of the advancing edge has a low yield (< 20%) and is usually not performed

  • In immunosuppressed patients, or if an unusual organism is suspected and there is no loculated site to culture, a full-thickness skin biopsy should be sent for routine histologic evaluation and for culture (bacterial, fungal, and mycobacterial)

  • If a primary source for the infection is identified (wound, leg ulcer, toe web intertrigo), cultures from these sites isolate the causative pathogen in half of cases

Diagnostic Procedures

  • ALT-70 is a predictive model to diagnose cellulitis or a cellulitis mimic and to provide guidance about when a dermatology consultation is needed

    • Variables are

      • Asymmetry (3 points)

      • Leukocytosis of 10,000/mcL (10 × 109/L) or more at presentation (2 points)

      • Tachycardia above 90 beats per minute (1 point)

      • Age 70 years or older (1 point)

    • Score above 5 carries more than an 82% chance of a true cellulitis while a score below 2 suggests a greater than 83% chance of a cellulitis mimicker



  • Intravenous or parenteral antibiotics may be required for the first 2–5 days, with adequate coverage for Streptococcus and Staphylococcus

  • Methicillin-susceptible S aureus (MSSA) can be treated ...

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