Epidemiology and Etiology
S. aureus (MSSA, MRSA).
Other Organisms Less common.
Sterile abscess can occur as a foreign-body response (splinter, ruptured inclusion cyst, injection sites). Cutaneous odontogenic sinus can appear anywhere on the lower face, even at sites distant from the origin (see Cutaneous Odontogenic [Dental] Abscess, Section 33).
Folliculitis, furuncles, and carbuncles represent a continuum of severity of S. aureus infection. Portal of entry: Ostium of hair follicle.
ABSCESS May arise in any organ or tissue. Abscesses that present on the skin arise in the dermis, subcutaneous fat, muscle, or a variety of deeper structures. Initially, a tender red nodule forms. In time (days to weeks), pus collects within a central space (Fig. 25-15A-C). A well-formed abscess is characterized by fluctuance of the central portion of the lesion. Arise at sites of trauma. Ruptured inclusion cyst on the back often presents as painful abscess. When arising from S. aureus folliculitis, it may be solitary or multiple.
FOLLICULITIS Begins in the upper portion of the hair follicle. Can arise from bacteria, fungi, virus, and mites. Follicular papule, pustule, erosion, or crust at the follicular infundibulum, and can extend deeper into the entire length of the follicle (sycosis). Usually nontender or slightly tender; may be pruritic (Fig. 25-16A and B). Predisposing factors include shaving hairy regions, occlusion of hair-bearing areas, topical corticosteroid preparations, systemic antibiotic promotes growth of gram-negative bacteria, diabetes mellitus, and immunosuppression. Extension of infection can progress to abscess or furuncle formation.
S. aureus Folliculitis can be either superficial folliculitis (infundibular) (Fig. 25-16) or deep (sycosis) (extension beneath infundibulum) (Fig. 25-17) with abscess formation. In severe cases (lupoid sycosis), the pilosebaceous units may be destroyed and replaced by fibrous scar tissue.
GRAM-NEGATIVE FOLLICULITIS Occurs in individuals with acne vulgaris treated with oral antibiotics. "Acne" typically worsens, having been in good control. Characterized by small follicular pustules and/or larger abscesses on the cheeks.
HOT-TUB FOLLICULITIS(P. aeruginosa). Occurs on the trunk following immersion in spa water (Fig. 25-18A and B).
Differential Diagnosis
FOLLICULITIS Acneiform disorders (acne vulgaris, rosacea, or perioral dermatitis), HIV-associated eosinophilic folliculitis, chemical irritants (chloracne), acneiform adverse cutaneous drug reactions (epidermal growth factor receptor inhibitors [e.g., erlotinib], halogens, glucocorticoids, lithium), keloidal folliculitis, and pseudofolliculitis barbae.
PAINFUL DERMAL/SUBCUTANEOUS NODULE Ruptured epidermoid or pilar cyst, hidradenitis suppurativa.
Course
Most cases of folliculitis and abscesses resolve with effective treatment. If diagnosis and treatment are delayed, furunculosis can be complicated by soft-tissue infection, bacteremia, and hematogenous seeding of viscera. Some individuals are subject to recurrent furunculosis, particularly diabetics.
PROPHYLAXISCorrect underlying predisposing condition. Washing with antibacterial soap or benzoyl peroxide preparation or isopropyl/ethanol gel.
ANTIMICROBIAL THERAPYBacterial Folliculitis Most will respond to natural penicillins but can consider dicloxacillin, amoxicillin, primary cephalosporins, and clindamycin, usually for 7 to 10 days. Consider culture for resistant organisms. Minocycline, trimethoprim-sulfamethoxazole, and quinolones may be necessary. There may be higher resistance to the erythromycin family.
Gram-Negative Folliculitis Associated with systemic antibiotic therapy of acne vulgaris. Discontinue current antibiotics. Wash with benzoyl peroxide. In some cases, ampicillin (250 mg four times daily) or trimethoprim-sulfamethoxazole four times daily. Isotretinoin.
The treatment of an abscess, furuncle, or carbuncle is incision and drainage, with consideration of systemic antimicrobial therapy in immunocompromised patients or when there are signs of systemic infection.
FURUNCLE Initially, a firm tender nodule, up to 1 to 2 cm in diameter. In many individuals, furuncles occur in the setting of staphylococcal folliculitis. Nodule becomes fluctuant, with abscess formation ± central pustule. Nodule with cavitation remains after drainage of abscess. A variable zone of cellulitis may surround the furuncle. Distribution: Any hair-bearing region—beard area, posterior neck and occipital scalp, axillae, buttocks. Solitary or multiple lesions (Figs. 25-19, 25-20, 25-21, 25-22, 25-23).
CARBUNCLE Evolution is similar to that of furuncle. Composed of several to multiple, adjacent, and coalescing furuncles (Fig. 25-24). Characterized by multiple loculated dermal and subcutaneous abscesses, superficial pustules, necrotic plugs, and sieve-like openings draining pus.