A patient has spreading erythema and fever over the leg. What is the most likely diagnosis and initial therapy?

• A. DVT
• B. Cellulitis; treat with appropriate antibiotics (oral for mild, IV for severe)
• C. Erysipelas
• D. Necrotizing fasciitis

Answer: (B)

The spreading red, warm area on the leg with fever is most consistent with cellulitis, an infection of the dermis and subcutaneous tissue. This presents with warmth, tenderness, and expanding erythema, and fever often accompanies skin-tight inflammatory signs. Erysipelas would usually show a well‑defined, raised border; necrotizing fasciitis would have severe pain out of proportion, rapid progression, and systemic toxicity; a DVT would cause swelling and leg pain but fever and spreading erythema are not typical early features.

Initial therapy targets the common organisms: streptococci and Staphylococcus aureus. For a mild, nonpurulent case, outpatient oral antibiotics that cover these organisms are appropriate (for example, agents like cephalexin or dicloxacillin). If there are purulent lesions or MRSA risk factors, or if there’s significant systemic illness, escalate to antibiotics with MRSA coverage (such as doxycycline, TMP-SMX, or clindamycin). If there are signs of systemic illness or the infection is extensive, hospitalize and start IV antibiotics (often vancomycin or linezolid for MRSA coverage, with a beta-lactam as needed for broader coverage). The key is initiating antibiotic therapy promptly and tailoring the choice to severity and MRSA risk.