Cellulitis vs abscess
Formal Definition
Cellulitis is a diffuse bacterial infection of the dermis and subcutaneous tissue without a defined fluid collection, treated with antibiotics; an abscess is a walled-off collection of pus requiring incision and drainage (I&D) as primary treatment, with antibiotics as adjunct only in select cases.
How It's Used on the Ward
"Is it fluctuant?" — the key exam question that determines whether to cut or not. Fluctuance = abscess = drain it. No fluctuance = cellulitis = antibiotics.
Example
""Arm injection site with an area of erythema and warmth: palpating for fluctuance — yes, there is a soft, boggy center about 3 cm in diameter. This is an abscess, not just cellulitis. Bedside I&D under local anesthesia, wound packing, and trim antibiotics to MRSA coverage.""
Clinical Context
Distinguishing the two is the most important soft tissue infection skill. Fluctuance on exam (soft, "wave-like" sensation) = abscess = I&D is definitive treatment. Bedside ultrasound dramatically improves accuracy when exam is unclear (sensitivity >90% vs ~50% for exam alone). Cellulitis: erythema without fluctuance, use beta-lactam (strep coverage) unless MRSA risk factors. Abscess: I&D is primary, MRSA coverage (TMP-SMX or doxycycline) if systemic signs or immunocompromise. After I&D, pack wound, verify all loculations broken up.