Ultrasound for Uncomplicated Cellulitis

Diagnosis and Imaging

Uncomplicated cellulitis presenting with typical features, such as localized erythema, edema, warmth, and tenderness, without systemic toxicity, should be diagnosed clinically without any imaging studies, as recommended by the Infectious Diseases Society of America 1
Plain radiographs have a minimal role in cellulitis evaluation and should not be used to rule out infection, according to the Clinical Infectious Diseases guidelines 2

Systemic toxicity indicators, such as fever, hypothermia, tachycardia, or hypotension, require immediate imaging, as stated by the Clinical Infectious Diseases guidelines 1
Signs of deep or necrotizing infection, including pain disproportionate to physical findings, violaceous bullae, or skin sloughing, necessitate imaging, as recommended by the Clinical Infectious Diseases guidelines 1
Failure to respond to appropriate first-line antibiotics after 48-72 hours is a red flag requiring imaging, according to the Praxis Medical Insights guidelines 2

High-resolution ultrasound or CT scanning can detect deep soft-tissue abscesses or sinus tracts when clinical suspicion exists, as stated by the Clinical Infectious Diseases guidelines 3
CT with IV contrast is superior for evaluating the extent of infection, fascial involvement, and complications requiring surgical intervention, according to the Praxis Medical Insights guidelines 2
For diabetic foot infections, plain radiographs and MRI are best for detecting bone involvement, and MRI provides anatomic information about sinus tracts, abscesses, or muscle involvement, as recommended by the Clinical Infectious Diseases guidelines 3

Over-ordering imaging for typical cellulitis wastes resources and delays appropriate antibiotic therapy, as stated by the Praxis Medical Insights guidelines 2
Assuming normal imaging excludes infection is incorrect, as cellulitis remains a clinical diagnosis even with negative imaging, according to the Praxis Medical Insights guidelines 2
Delaying surgical consultation while waiting for imaging when necrotizing infection is suspected is a pitfall, as emergent surgical evaluation takes priority, as recommended by the Clinical Infectious Diseases guidelines 1