Overview
Also known as a boil, a furuncle is the infection of a hair follicle leading to a small abscess forming in the subcutaneous tissue, resulting in a deep-seated inflammatory nodule. A carbuncle describes several adjacent boils joining beneath the skin, resulting in an inflammatory mass draining pus.
Furuncles and carbuncles are most commonly caused by Staphylococcus aureus. Nasal carriage of Staphylococcus aureus may increase the risk of recurrent furuncles and carbuncles.
Epidemiology
- Furuncles are common in adolescents and young adults
- Carbuncles are less common and are usually seen in middle-aged/older men
Risk Factors
- Male sex
- Adolescence/young adult
- Close contact with a person with infection
- Contact sports (e.g. wrestling)
- Poor hygiene and overcrowding
- Concomitant skin lesions (e.g. eczema, abrasions)
- Immunocompromised states – HIV, corticosteroids, immunosuppressants, diabetes mellitus
- Obesity
- Malnutrition
Presentation
Overview
Features of a furuncle include:
- Firm, tender, erythematous nodule that may feel fluctuant or ‘boggy’
- Their size can range from pea-sized to golf-ball-sized
- They can rupture spontaneously and leave a violaceous macule
- The overlying skin may be shiny
- Often found on hairy skin (e.g. face, neck, axillae, buttocks)
- Mild constitutional symptoms – mainly fever
- There may be surrounding cellulitis
Features of a carbuncle include:
- Larger, erythematous, hard, dome-shaped, very painful lump
- Often increases in size over a few days
- Often found at the nape of the neck, back, or thighs
- They may develop a yellow-grey irregular central crater due to skin necrosis
- Constitutional symptoms are worse – often high fever and malaise
- There may be associated regional lymphadenopathy
Diagnosis
Furuncles and carbuncles are diagnosed clinically. In some cases, if a furuncle or carbuncle is unresponsive to treatment, persistent, or recurrent, swabs may be taken to exclude other organisms or Panton-Valentine leukocidin Staphylococcus aureus (PVL-SA), which can cause recurrent furuncles and carbuncles and serious complications.
Management
Incision and drainage
If any of the following features apply, arrange for same-day incision and drainage:
- All large and/or fluctuant furuncles
- All carbuncles
Hospital admission
If any of the following apply, consider admission for intravenous antibiotics:
- Systemically unwell
- Cellulitis is present
- Areas with a high risk of serious complications – such as the face
- Immunocompromised state
Hospital admission and drainage not indicated
With smaller, uncomplicated furuncles applying moist heat (e.g. a warm, damp towel) can alleviate pain, promote spontaneous drainage, and localise infection.
- Patients should be safety-netted to seek help if lesions become fluctuant and/or if they become systemically unwell or develop cellulitis
In some cases, a 7-day course of oral antibiotics may be necessary, particularly if any of the following apply:
- Febrile
- Cellulitis is present
- Facial lesion
- Pain/severe discomfort
- Other comorbidities (e.g. diabetes mellitus and immunosuppression)
The antibiotic of choice is flucloxacillin or if allergic, clarithromycin or erythromycin (for pregnant/breastfeeding people).
Complications
Scarring – this can sometimes be permanent and is more likely with carbuncles.
Infection spread – this can lead to cellulitis, thrombophlebitis, and in some cases, septic arthritis, osteomyelitis, infectious endocarditis, and sepsis.
Cavernous sinus thrombosis – rare, but can occur due to furuncles or carbuncles on the face.
Prognosis
- Most furuncles heal without complications. However, people with nasal Staphylococcal aureus colonisation can have recurrent episodes
- Carbuncles can heal slowly and leave a scar
