Boils and Carbuncles

The incidence of boils is uncertain. They are rare in children except in those with atopic eczema. They are rather more common in adolescents and in early adulthood, especially in boys and the peak incidence is the same as for acne vulgaris.

Boils

There is usually no predisposing cause, although boils may complicate atopic dermatitis, excoriations, abrasions, scabies or pediculosis. Staphylococcal colonisation is more common on atopic eczema and may contribute to the pathogenesis.¹

• The evidence to link diabetes with furunculosis (multiple crops of boils) is conflicting but when boils affect people with diabetes, they tend to be more extensive.
• Other conditions associated with furunculosis include obesity² and immune compromise as with HIV, blood dyscrasias and treatment with immunosuppressive drugs.

Carbuncles

• Carbuncles are associated with malnutrition, heart failure, drug addiction, severe generalised skin disease and prolonged steroid therapy.
• The evidence is conflicting with regard to association with diabetes.
• In adults the use of topical steroids is associated with the development of folliculitis.

Boils

• A boil starts as a hard, tender, red nodule surrounding a hair follicle. It enlarges and becomes fluctuant over several days as an abscess forms.
• Later it may discharge pus from its centre, before healing and it may leave a scar.
• Boils arise in hair-bearing areas, especially where there is friction, occlusion and perspiration. This includes the neck, face, axillae, arms, wrists, fingers, buttocks and anogenital region.
• Boils may be isolated or multiple lesions; the latter is particularly likely on the buttocks.
• There are sometimes mild constitutional symptoms, such as fever and malaise.

Carbuncles

• A carbuncle starts as a smooth, dome-shaped, acutely tender, painful lesion. It often occurs at the nape of the neck, the back, or thighs, and develops into a swollen, painful area discharging pus from several sites.
• Constitutional symptoms, such as fever and malaise may accompany or even precede the development of the carbuncle.

It is usually safe to assume that this is a staphylococcal infection, but in persistent or recurrent infection swabs should be taken from the nose, throat, umbilicus, axillae and perineum. Culture and sensitivities are required.

If there are multiple, severe or recurrent infections, full blood count and fasting blood glucose are indicated.

• Cystic acne; shows papules and comedones and is usually confined to the face and trunk, especially the back.
• Hidradenitis suppurativa; is a bacterial infection of the apocrine glands - only the groin and the axillae are involved.
• Infected epidermal inclusion cyst (also known as sebaceous cyst) should also be considered.
• Cellulitis; localised skin inflammation increasing in size as the infection spreads with tight, glossy, "stretched" appearance of the skin.
• Osteomyelitis; may be present in underlying tissue.
• Orf; starts as a small, firm red or reddish blue lump that enlarges to form a flat-topped, blood-tinged pustule or blister. It is usually 2 to 3 cm in diameter, but may be as large as 5 cm. It should be considered in rural communities
• Anthrax can resemble a carbuncle, but has a distinctive haemorrhagic crust and vesicular margin. Again contact with animals is usual.
• Herpetic whitlow; differs from a staphylococcal whitlow in that there is usually a history of previous lesions at the same site. Lesions present with a group of haemorrhagic vesicles that may become confluent and form a single bulla.

• If lesions are not fluctuant (fluctuance is a wave-like feeling on palpating skin overlying a fluid-filled cavity with nonrigid walls e.g. a cavity containing pus) the application of moist heat 3-4x/day relieves discomfort, helps localise the infection and promotes drainage.
• Treatment with oral antibiotics (until the inflammation resolves) is recommended:
  • If there is fever or surrounding cellulitis then oral antibiotics for 7 days are indicated.
  • If infection occurs where complications can be dangerous e.g. the face, antibiotics should be started promptly.
  • If there is a large area of cellulitis.
  • If there is significant co-morbidity e.g. diabetes or immunocompromise.
• Oral flucloxacillin is usually the drug of choice against S. aureus with erythromycin or clarithromycin if penicillin is contraindicated.
• Methicillin resistant S. aureus (MRSA) is a growing threat in hospitals but it also being reported in the community.⁴
• Drainage may be spontaneous or surgical, but cover the lesion with a sterile dressing to prevent autoinoculation.
• Incision and drainage is indicated for lesions that are large, localised, painful, and fluctuant.

Observe the patient for signs of systemic upset. Most cases can be treated in primary care, but the decision of whether to admit the person will depend on clinical judgement, taking into account the rapidity and degree of spread and co-morbidities e.g. diabetes.

Persistent and recurrent infection

• In persistent or recurrent infection, swabs should be taken for culture and sensitivities.
• Exclude underlying causes e.g. systemic disease, that may have compromised the immune system. Also consider skin disease e.g. scabies, pediculosis or eczema.
• There may industrial exposure to chemicals or oils or simply poor hygiene.
• Consider sources of infection such as autoinoculation, pyogenic infections in family members and contact sports.
• S. aureus is a persistent part of normal microbial flora in 10 to 20% of the population and around 30 to 50% of healthy adults are colonised with S. aureus at some site, at any given time.
• If furunculosis persists after screening and treating the person, consider outside sources of infection such as family and close contacts. Overt infections is more likely as a source than asymptomatic carriage, but consider screening household members, if they will co-operate.

Extraneous sources of infection

• Eradication of nasal carriage of staphylococci can be achieved with a cream of chlorhexidine with neomycin (Naseptin) applied to the nostrils four times a day for 10 days. Re-colonisation is common. Mupirocin nasal ointment is excellent at eliminating nasal staphylococci, but should be reserved for resistant cases.⁵
• If other sites are involved then oral antibiotics may be necessary. The choice is guided by sensitivities.
• Antiseptics can reduce staphylococci on the skin. Washing the body and hair daily, and bathing in an antiseptic solution of chlorhexidine or triclosan (e.g. Hibiscrub ®) in a detergent vehicle helps eliminate infection. If there is dry or inflamed skin then an antiseptic emollient should be used. Examples include Dermol 500®, Oilatum Plus®, Emulsiderm® or Dermol 600®.
• The patient should also:
  • Wash sheets and underwear regularly in a hot wash (above 55°C). The clothes should be turned inside out and the machine not overloaded so that the water can penetrate.
  • Thoroughly clean the bedroom when treatment is started.
  • Maintain a personal towel and flannel, and rinse the flannel in hot water before use.
• Oral flucloxacillin or erythromycin are usually effective against S. aureus infections. There is no evidence base for the best duration of treatment, but 7 days treatment is generally recommended.
• In chronic furunculosis the choice of antibiotic ideally should be guided by sensitivities. Flucloxacillin is recommended for blind treatment or erythromycin if there is a penicillin allergy. Treat for 2 weeks initially, but some people will need a longer course of perhaps 6 or 8 weeks.

• Boils and carbuncles can leave scars.
• Surrounding cellulitis or bacteraemia may develop if furunculosis or carbuncles extend.
• Cavernous sinus thrombosis can complicate boils or carbuncles on the face, but this is rare.
• Metastatic infection is rare, but can include osteomyelitis, acute endocarditis or brain abscess. Septicaemia is a very rare complication of both furuncles and carbuncles.

• Over a course of 2 days to 3 weeks the boil becomes necrotic and develops into an abscess. It ruptures and discharges pus and often a core of necrotic material. Pain subsides as pressure is reduced, and the redness and oedema diminish over days to weeks.
• In people who have HIV boils may coalesce into violaceous plaques.
• A carbuncle grows in size for a few days to reach a diameter of 3 to 10 cm, occasionally more. After 5 to 7 days suppuration occurs and multiple pustules soon appear on the surface, draining externally around multiple hair follicles.
  • A yellow-grey irregular crater develops at the centre. In some cases the necrosis develops more acutely without a follicular discharge and the entire central core is shed to leave a deep ulcer with a purulent floor.
  • Healing takes place slowly by granulation and the area may remain deeply violaceous for a prolonged period of time.
  • Death may occur in the frail and ill from toxaemia or from metastatic infection.