Cellulitis

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 interdigital tinea pedis with fissuring

• 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

Diagnosis

Laboratory Tests

• Leukocytosis or 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

Treatment

Medications

• 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 with

  • Nafcillin

  • Cefazolin

  • Clindamycin

  • Dicloxacillin

  • Cephalexin

  • Doxycycline

  • Trimethoprim-sulfamethoxazole (TMP-SMZ)

• If MRSA ...