Dermatology · PANCE / PANRE

Cutaneous Abscess, Furuncle, Carbuncle

Purulent skin and soft tissue infections of the hair follicle and surrounding dermis; most caused by S. aureus, increasingly MRSA.

Also known as: abscess, boil, furuncle, carbuncle, skin abscess, MRSA, folliculitis

Overview

Purulent bacterial infections of the skin and subcutaneous tissue. Folliculitis = inflammation of a hair follicle (superficial). Furuncle (boil) = deep follicular abscess. Carbuncle = coalesced cluster of adjacent furuncles with multiple sinus tracts. Abscess (more general) = localized collection of pus within a cavity.

Epidemiology

Most common SSTI presentation in US ambulatory care; ~3 million ED visits annually. Community-acquired MRSA (USA300 strain) now accounts for >50% of purulent SSTIs in many US regions.

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Risk factors

S. aureus colonization (nares, axillae, groin)
Skin trauma, IV drug use, athletes (wrestling, football), crowded living, daycare, prisons, military
Diabetes, obesity, atopic dermatitis, hidradenitis suppurativa
Immunosuppression — HIV, transplant, neutropenia
Prior antibiotic use (selects for MRSA)
Foreign bodies, retained sutures, prosthetic devices

Pathophysiology

S. aureus (including MRSA) enters through follicular ostia or skin breaks → bacterial proliferation → robust neutrophilic response → liquefactive necrosis → fluctuant abscess. PVL (Panton-Valentine leukocidin) toxin in CA-MRSA contributes to tissue necrosis and recurrent disease.

Clinical presentation

Symptoms

Painful, tender, warm swelling
Spontaneous drainage of pus
Mild fever and constitutional symptoms (severe systemic symptoms suggest deeper or invasive infection)
Recurrent boils (especially MRSA) frustrating patient and family

Signs / physical exam

Folliculitis: small (1-5 mm) erythematous papules and pustules centered on hair follicles; usually no fluctuance
Furuncle: deep tender erythematous nodule (1-2 cm) with central pustule; eventual fluctuance and spontaneous drainage
Carbuncle: large, deep, tender plaque with multiple draining openings on neck, back, thighs; more systemic illness
Abscess: well-circumscribed tender fluctuant nodule with surrounding erythema; pointing pustule or already drained
Lymphangitis (red streaking) or regional lymphadenopathy if more advanced
Systemic signs of sepsis: tachycardia, hypotension, fever — indicates need for hospitalization and IV antibiotics

Classic findings

Tender erythematous fluctuant nodule that 'points' or drains pus; carbuncle = multifocal cluster with sinus tracts.

Differential diagnosis

Cellulitis (non-purulent) — Diffuse warmth, erythema, edema without focal fluctuance; group A strep or MSSA; no I&D needed
Hidradenitis suppurativa — Recurrent abscesses in intertriginous areas with sinus tracts and scarring
Pilonidal cyst/abscess — Sacrococcygeal location with hair tuft
Epidermoid (sebaceous) cyst — Painless mobile nodule with central punctum; if infected, manage as abscess but excise wall after resolution
Sporotrichosis / atypical mycobacteria — Chronic nodular lymphangitic spread; gardening / aquarium / hot tub exposure
Necrotizing fasciitis — Pain disproportionate to exam, rapid progression, crepitus, systemic toxicity, hypotension; SURGICAL EMERGENCY
Erysipelas — Sharply demarcated raised erythematous plaque, fever, group A strep
Tularemia / anthrax / bartonella — Specific exposure history, eschar (anthrax), regional lymphadenopathy

Diagnostic workup

Diagnostic criteria

Clinical: fluctuant tender nodule; ultrasound confirms collection; culture identifies pathogen and susceptibility.

Labs

Most uncomplicated abscesses require no labs — I&D is diagnostic and therapeutic
Wound culture from drained pus if: severe, treatment-failure, immunocompromised, recurrent, atypical exposure
CBC, BMP, blood cultures if systemic illness (fever, tachycardia, hypotension)
HbA1c if recurrent disease
HIV testing if otherwise unexplained recurrent severe infections

Imaging

Bedside ultrasound to distinguish cellulitis from abscess and identify pockets when clinical exam ambiguous
CT/MRI for deep abscess, suspected necrotizing fasciitis (NF), perirectal abscess, complex anatomy

Diagnostic algorithm

flowchart TD
  A[Tender erythematous nodule] --> B{Fluctuant?}
  B -->|No / cellulitis| C[Empiric oral antibiotic<br/>cephalexin if strep/MSSA;<br/>add MRSA if purulent risk]
  B -->|Yes / abscess| D[Incision & Drainage]
  D --> E{Severity / Risk Features?}
  E -->|Small <2 cm, immunocompetent, no cellulitis| F[I&D alone may suffice]
  E -->|>2 cm, cellulitis, systemic Sx,<br/>immunocompromised, facial, recurrent| G[I&D + oral antibiotic<br/>TMP-SMX, doxy, or clindamycin]
  E -->|Sepsis, NF concern| H[Admit / IV antibiotics<br/>vancomycin ± piperacillin-tazobactam]
  H --> I[Surgical consult for necrotizing infection]
  G --> J{Recurrent furunculosis?}
  J -->|Yes| K[Decolonize household:<br/>intranasal mupirocin + chlorhexidine]

Cutaneous abscess and furuncle: I&D-centered management algorithm.

Treatment

First-line

Incision and drainage (I&D) is the cornerstone of therapy — single most important intervention
• Linear incision over fluctuant point with #11 blade
• Express purulent material, break loculations with hemostat
• Irrigate copiously with saline
• Loose packing for large cavities (questionable benefit for <5 cm abscesses)
• Loop drainage and minimally invasive techniques as alternatives
Antibiotic therapy AFTER I&D (IDSA 2014 update — initially considered unnecessary for uncomplicated):
• Recommended for: abscess >2 cm, multiple lesions, surrounding cellulitis, systemic signs, immunocompromised, very young/old, recurrent, failure of prior I&D, facial location
• MRSA coverage: trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 DS tablets BID × 7-10 days OR doxycycline 100 mg BID OR clindamycin 300-450 mg QID (check D-test for inducible resistance)
• MSSA-only: cephalexin 500 mg QID or dicloxacillin 500 mg QID
• Empiric for severe: IV vancomycin, linezolid, daptomycin, or ceftaroline
Warm compresses to facilitate pointing and drainage
Pain control with acetaminophen, NSAIDs

Recurrent furunculosis (decolonization)

Intranasal mupirocin 2% ointment BID × 5 days
Chlorhexidine 4% wash daily for body × 5 days
Decolonize all household members simultaneously
Launder linens and clothing in hot water
Address underlying conditions: diabetes, eczema, HS

Facial / central face (danger triangle)

Avoid I&D of small lesions in danger triangle (between nose and upper lip) — theoretical risk of septic cavernous sinus thrombosis (rare with antibiotic era but caution remains)
Treat with antibiotics; I&D only if significant collection

Carbuncle / complex deep abscess

Surgical incision and debridement under regional anesthesia
Wider antibiotic coverage including IV options if systemic toxicity
Address comorbidities (diabetes, immunosuppression)

Second-line / adjunct

Bleach baths (1/4 to 1/2 cup household bleach in full tub) twice weekly for recurrent disease (especially with atopic dermatitis)
Hot tub folliculitis (Pseudomonas aeruginosa) — self-limited, supportive care; ciprofloxacin only for immunocompromised or severe
Gram-negative folliculitis (post-antibiotic acne treatment) — discontinue antibiotic, switch class
Tinea barbae / sycosis barbae — antifungal not antibacterial therapy

Complications

Spread to adjacent soft tissue → cellulitis, lymphangitis
Bacteremia and sepsis
Endocarditis (especially with IV drug use)
Osteomyelitis, septic arthritis
Necrotizing fasciitis (rare but life-threatening)
Cavernous sinus thrombosis from facial 'danger triangle' infections (very rare with antibiotics)
Scarring, especially after carbuncle
Antibiotic adverse effects: C. difficile colitis (clindamycin), photosensitivity (doxycycline), SJS/hyperkalemia (TMP-SMX)

PANCE pearls

I&D is the primary treatment — antibiotics WITHOUT I&D usually fail.
TMP-SMX and doxycycline cover MRSA but NOT group A strep — for cellulitis without abscess, use cephalexin or add coverage.
Bedside ultrasound is invaluable for ambiguous fluctuance — show the patient and document.
Recurrent furunculosis requires decolonization of the patient AND all household members — intranasal mupirocin + chlorhexidine washes.
Pain disproportionate to exam, rapid spreading erythema, crepitus, or systemic toxicity = necrotizing fasciitis until proven otherwise — surgical emergency.

References

IDSA 2014 — Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America (Stevens et al., Clin Infect Dis 2014)
Liu CA-MRSA 2011 — Clinical Practice Guidelines by the Infectious Diseases Society of America for the Treatment of MRSA Infections in Adults and Children (Liu et al., Clin Infect Dis 2011)
CDC MRSA — CDC Healthcare-Associated Infections and MRSA Clinical Guidance

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