Doctors Revision

Dermatology (Skin Conditions)

Furuncle / Carbuncle

A furuncle (boil) is a deep infection of a hair follicle leading to an abscess. A carbuncle is a larger, deeper lesion formed by the interconnection of multiple furuncles, often with multiple drainage points.

Also known as: Boil, Abscess (superficial)

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Referral and warning signs

When to refer

Refer if: Large carbuncle, Lesion on face (danger triangle), Signs of systemic illness/sepsis, Immunocompromised patient, Failure to resolve with initial management, Recurrent furunculosis (for investigation/decolonization).

Red flags

  • Lesion within the facial 'danger triangle' (area from corners of mouth to bridge of nose).
  • High fever / Systemic toxicity.
  • Rapidly spreading redness/cellulitis.
  • Neurological signs (if facial lesion - cavernous sinus thrombosis).
  • Failure of fluctuant lesion to drain after I&D.

Signs and symptoms

  • Furuncle: Starts as tender, red nodule around a hair follicle. Becomes painful, fluctuant (pus-filled), and may develop a central 'head' or point before spontaneously draining.
  • Carbuncle: Larger, deeper, multi-headed lesion. Often on back of neck, shoulders, thighs. Associated with more systemic symptoms (fever, malaise).

Risk factors

  • Staphylococcus aureus carrier state (nose, skin).
  • Poor hygiene.
  • Friction from clothing.
  • Diabetes Mellitus.
  • Immunosuppression (HIV, malnutrition).
  • Obesity.
  • Pre-existing skin conditions.

Diagnosis

Clinical assessment

Diagnosis based on clinical appearance of a tender, erythematous, fluctuant nodule or larger carbuncle.

Differential diagnosis

  • Infected epidermal cyst.
  • Hidradenitis suppurativa.
  • Acne nodule/cyst.
  • Cellulitis (more diffuse).
  • Lymphadenitis.

Investigations

  • Usually clinical diagnosis.
  • Pus swab for Gram stain, Culture & Sensitivity (if drained, recurrent, or systemic antibiotics needed).
  • Blood glucose check (if recurrent or diabetic risk factors).
  • Consider HIV test if recurrent.

Diagnostic criteria

Clinical appearance of localized skin abscess related to hair follicle(s).

Management

Non-pharmacological management

  • Warm Compresses: Apply frequently to encourage localization and spontaneous drainage. (LOC: HC2)
  • Incision and Drainage (I&D): Definitive treatment once lesion is fluctuant. Perform under aseptic conditions, make incision over most fluctuant point, allow pus to drain, may need gentle exploration/breaking of loculations, consider packing cavity loosely with gauze wick (especially carbuncles) to allow continued drainage. (LOC: HC2/3)
  • Maintain good hygiene.

Pharmacological treatment

  • Antibiotics: Not always needed for simple, small furuncles drained effectively. Indications for antibiotics: Large size (carbuncle), Surrounding cellulitis, Location on face (risk of cavernous sinus thrombosis), Systemic symptoms (fever), Immunocompromised host, Recurrent infections.
  • - Choice (Cover Staph aureus): Cloxacillin 250-500 mg PO QID (before food) for 5-7 days. (Child: 12.5-25 mg/kg/dose). (LOC: HC2)
  • - Alternative (Penicillin Allergy): Erythromycin 500 mg PO QID. (Child: 7.5-12.5 mg/kg/dose). (LOC: HC2)
  • - Clindamycin or TMP-SMX may be considered if MRSA suspected.
  • Analgesia: Paracetamol or NSAIDs.

Monitoring

Monitor for resolution after drainage/antibiotics. Ensure packing removed appropriately (if used). Watch for signs of spreading infection.

Complications

  • Cellulitis.
  • Sepsis (rare).
  • Cavernous sinus thrombosis (if facial 'danger triangle' lesion).
  • Scarring.
  • Recurrence.

Prevention

  • Good personal hygiene, use of antiseptic soaps.
  • Treating underlying conditions (diabetes).
  • Consider decolonization therapy (e.g., mupirocin nasal ointment, antiseptic washes) for recurrent infections (specialist advice).

Patient education

  • Explanation of boil/carbuncle.
  • Importance of warm compresses.
  • Need for I&D if fluctuant.
  • How to care for wound after drainage.
  • Importance of completing antibiotics if prescribed.
  • Hygiene measures to prevent recurrence/spread.
  • Avoid squeezing lesions.

Uganda-specific notes

Common skin infections. I&D is key treatment for fluctuant lesions. Cloxacillin is standard antibiotic choice. Consider underlying HIV/diabetes in recurrent cases.

References

  • Uganda Clinical Guidelines (UCG) 2023

    Chapter 22, Section 22.1.2

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