Minor skin abscesses (boils) can be treated by incision and drainage without the need for systemic antimicrobials.
Recurrent abscesses (furunculosis) call for the identification of predisposing factors, improvement of personal hygiene and, if necessary, topical treatment of nasal staphylococcal colonisation.
Aetiology and terminology
The most common causative agent is Staphylococcus aureus.
If the inflammation is limited to the hair follicle the condition is called folliculitis (pictures 12).
If the inflammation spreads to the surrounding tissues the condition is referred to as an abscess (a furuncle, pictures 34).
An abscess may spread further via cutaneous interconnecting channels to form an aggregate of furuncles, i.e. a carbuncle.
Sycosis barbae (barber's itch) is deep folliculitis of the beard region (pictures 56).
Diagnosis
Diagnosis is based on clinical presentation.
Often seen on the face and hairy skin areas, scalp, groins, thighs and axillae.
Folliculitis manifests as a yellowish pustule of 1-3 mm diameter with surrounding erythema.
An abscess is a hot, red and painful lump under the skin, which may exude purulent material when “ripe”.
Investigations
Bacterial culture is only indicated in complicated or prolonged cases.
In the case of poor treatment response, the possibility of MRSA Multidrug-Resistant Bacteria in Hospitals should be kept in mind, especially if there is preceding history of travel or hospital care abroad.
Fungal samples (for microbiology and culture) whenever tinea is suspected.
Differential diagnosis
The most important differential diagnoses are the early stages of erysipelas, cellulitis and necrotising infections.
Keep in mind the possibility of secondary cellulitis if the patient has general symptoms or if the erythema extends widely outside the abscess area.
It is important to identify causes other than infectious ones.
Acne, acneiform drug eruptions, rosacea
Oily skin creams, occupational provoking factors (e.g. oils and halogenated hydrocarbons), skin occlusion (e.g. plasters), friction, sweating and maceration, hair removal with a razor blade.
In individuals with more pigmented skin types, pseudofolliculitis of the beard area (pseudofolliculitis barbae) and neck (acne cheloidalis nuchae).
The following pathogens may also cause a clinical picture that resembles folliculitis:
tinea (particularly around the beard area and scalp)
herpes and Herpes varicella-zoster (may cause grouped pustules)
gram-negative bacteria, such as Pseudomonas aeruginosa (for example, from dirty jacuzzi pools or following a long course of antimicrobials) or Malassezia yeast (on the back or chest).
Treatment
Topical treatment
The treatment of folliculitis is usually topical.
On hairy skin areas (e.g. thighs) superficial folliculitis is a physiological phenomenon that doesn't always need treatment.
The affected areas should be washed with soap or a low pH skin cleanser.
The dosage is determined based on the severity of the infection, not on the patient's weight.
Incision and drainage of an abscess
The mainstay of treatment is surgical incision and drainage.
In an acute phase the abscess is incised under local anaesthesia (for example, a scalpel blade no. 11).
The debridement of any infected necrotic tissue and pus is carried out with a suitable instrument and the cavity is rinsed with, for example, physiological saline.
A ribbon gauze dressing (e.g. Sorbact® ) may be left in the cavity to absorb the bacterial mass. The cavity is irrigated twice daily for a few days.
In addition to the above, an antimicrobial cream is used in mild cases.
Systemic antimicrobials after an incision and drainage of an abscess
Systemic antimicrobials are usually not indicated.
Systemic antimicrobials are indicated in the following instances: the patient has fever or general symptoms, the abscess is large and tissue damage extensive, the abscess is located in the nasal region or concomitant diseases make the patient susceptible to complications (diabetes, immune deficiency, artificial joint, use of glucocorticoids).
First-line antibicrobial drugs include cephalexin 500-750 mg 3 times daily, in children 50 mg/kg/day or flucloxacillin 750-1 000 mg 3 times daily; duration of treatment 7-10 days. Also other antimicrobials effective against S. aureus can be used: for example a combination of amoxicillin and clavulanic acid 875/125 mg twice daily.
If the abscess is caused by an infected epidermal cyst (picture 7), this should be removed together with its capsule once the acute phase has subsided.
Bacterial culture is indicated since MRSA may be the cause of recurrent furuncles.
Additionally, it is a good idea to ask the laboratory to determine PVL (Panton-Valentine leukocidin), i.e. an exotoxin specific to S. aureus bacteria. Both methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) S. aureus may produce it.
It is important to differentiate furunculosis from acne (e.g. acne conglobata Acne) and hidradenitis suppurativa (deep furuncular lesions in flexural sites).
The following measures are recommended in furunculosis: improved personal hygiene, antiseptic cleansing lotions (e.g. chlorhexidine or benzoyl peroxide) or antimicrobial creams, daily changing of bed linen, towels and clothing.
Predisposing factors should be investigated.
Moreover, the eradication of nasal S. aureus colonisation may be attempted with antibacterial creams, e.g. mupirocin cream twice daily for 5 days or fusidic acid cream for 1-2 weeks.
As an addition to the topical treatment in severe cases (> 3 recurrences/6 months), clindamycin 150 mg 1-2 times daily for 1-3 months may be given as prophylactic treatment. Antimicrobials from the tetracycline, sulpha and macrolide groups have also been used.
Consultation
Emergency treatment in a hospital and, if indicated, surgery is recommended in complicated abscesses, severe skin infections and septic conditions.
In furunculosis refractory to treatment, a specialist in dermatology or infectious diseases should be consulted (verification of diagnosis, implementation of more effective eradication treatment).
Pictures
References
Bartoszko JJ, Mertz D, Thabane L, et al. Antibiotic therapy for skin and soft tissue infections: a protocol for a systematic review and network meta-analysis. Syst Rev 2018;7(1):138. [PubMed]
Butler-Laporte G, De L'Étoile-Morel S, Cheng MP, et al. MRSA colonization status as a predictor of clinical infection: A systematic review and meta-analysis. J Infect 2018;77(6):489-495. [PubMed]
Wang W, Chen W, Liu Y, Siemieniuk RAC, Li L, Martínez JPD, Guyatt GH, Sun X. Wang W, Chen W, Liu Y, et al. Antibiotics for uncomplicated skin abscesses: systematic review and network meta-analysis. BMJ Open 2018;8(2):e020991. [PubMed]
Vermandere M, Aertgeerts B, Agoritsas T, Liu C, Burgers J, Merglen A, Okwen PM, Lytvyn L, Chua S, Vandvik PO, Guyatt GH, Beltran-Arroyave C, Lavergne V, Speeckaert R, Steen FE, Arteaga V, Sender R, McLeod S, Sun X, Wang W, Siemieniuk RAC. Vermandere M, Aertgeerts B, Agoritsas T, et al. Antibiotics after incision and drainage for uncomplicated skin abscesses: a clinical practice guideline. BMJ 2018;(360):k243. [PubMed]