An abscess is a localized inflammatory process in which the white blood cells accumulate at the site of infection in the dermis and/or subcutaneous tissue, creating a collection of pus. Commonly associated pathogens are Staphylococcus aureus, streptococci, and normal skin flora. Trauma or any break in the skin barrier predisposes to abscess formation.
Lesions evolve over days to 1-2 weeks. They are usually painful / tender, erythematous, warm, and fluctuant masses that are sometimes associated with fever. A tender subcutaneous nodule with overlying erythema but minimal fluctuance may be an early presentation. Incision and drainage is the mainstay of therapy. In an otherwise healthy, ambulatory patient, the addition of antibiotics is not indicated. Indications for the addition of antibiotics may include patients who are systemically ill, have a high burden of disease (indicated by concomitant widespread folliculitis or associated cellulitis), are immunosuppressed, or have failed incision and drainage.
Methicillin-resistant S. aureus (MRSA) first emerged as an important nosocomial pathogen in the 1960s. In more recent years, community-acquired outbreaks of MRSA (CA-MRSA) have increasingly been described among healthy individuals lacking the traditional risk factors for such infections (intravenous [IV] drug use, incarceration, participation in contact sports, etc). These strains have a propensity for causing abscesses, furunculosis, and folliculitis and have a unique antibiotic susceptibility profile from health care-associated strains of MRSA (HA-MRSA).
It has been shown that the majority of purulent skin and soft tissue infections presenting to emergency rooms across the United States are caused by CA-MRSA.
Codes
ICD10CM: L02.91 – Cutaneous abscess, unspecified
SNOMEDCT: 31928004 – Abscess of skin AND/OR subcutaneous tissue
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Differential Diagnosis & Pitfalls
Kerions on the scalp are fungal-induced hypersensitivity reactions, commonly associated with adenopathy, and difficult to tell from bacterial-induced abscesses.
Mycobacterial infections present as a "cold abscess" (little to no erythema or warmth) in a normal host.
Aspergillosis and other opportunistic infections, including Mycobacterium avium complex and Serratia, can present as an abscess in the immunocompromised patient.
The differential diagnosis of a tender, erythematous dermal or subcutaneous nodule in the immunosuppressed host must include bacterial, fungal, and mycobacterial organisms. These cannot be differentiated clinically and must be cultured to determine the causative organism.
