Pathoanatomy—It is infection of dermis and subcutaneous tissue without associated abscess.

Mechanism—Infection is through bacterial breach of cutaneous surface, however, a break in the skin is not required for spread of bacteria

Epidemiology in the United States is about 14.5 million cases annually with approximately 12% in the upper extremity, with a slight male predominance

Risk factors include trauma, IV drug use, immunocompromised patients, diabetes mellitus, steroid use, skin disorders (eczema, shingles), obesity

History reveals pain, fever, abrasion, puncture wound, or insect bite, expanding erythema

Physical examination shows erythematous, swollen, painful hand, which may have associated lymphangitis

Laboratory studies present elevated WBC, ESR, CRP, and lactate (lack specificity), <5% have a positive blood culture, skin biopsy yields a pathogen in 20% to 30% of cases—culture and biopsy are not recommended

Imaging—Radiographs will show soft tissue swelling without bony pathology

Classification—Infection is classified as mild (no systemic signs), moderate (has systemic signs), severe (has systemic signs, purulence, and is rapidly evolving)