Skin abscess
Some skin abscesses can develop into serious complications requiring prompt medical attention. The presence of high fever, chills, rapidly spreading redness around the lesion, red streaks going up towards the lymph nodes (lymphangitis), an abscess on the face around the nasolabial triangle, or an altered general condition in an immunocompromised or diabetic person, should prompt the patient to seek medical attention without delay, or to call for help if there are signs of sepsis.
Pathophysiology and formation mechanisms
The formation of a skin abscess results from an imbalance between bacterial virulence and the host's local defences. This process follows a relatively stereotyped pathophysiological sequence, irrespective of location or causative agent.
| Step | Mechanism | Clinical manifestation |
|---|---|---|
| Bacterial inoculation | Bacterial penetration through a skin breach (wound, puncture, clogged hair follicle, sweat gland) or by contiguity from an adjacent infection site. | Often asymptomatic stage or discrete initial local reddening |
| Acute local inflammation | Recruitment of neutrophils, release of inflammatory mediators, vasodilation and increased capillary permeability | Localized redness, heat, swelling and pain are the cardinal signs of inflammation. |
| Necrosis and tissue liquefaction | Tissue destruction by bacterial enzymes (proteases, staphylolysins) and dead polynuclei forming pus | Appearance of a fluid collection under tension, palpable, fluctuating on examination |
| Abscess maturation | Formation of a pyogenic membrane delimiting the purulent cavity, the body's attempt to contain the infection | Constituted, well-defined, fluctuating abscess with a maturation point in the skin (central softening zone) |
| Spontaneous evolution | If left untreated, the abscess may fistulate spontaneously in the skin, evacuating its contents, or spread to adjacent tissues. | Partial spontaneous evacuation or extension to cellulitis, fasciitis or bacteremia |
Bacterial agents involved
Staphylococcus aureus is by far the most common causative agent of skin abscesses, regardless of location. Other bacteria may be involved, depending on the clinical context, anatomical location and the patient's background.
| Bacterial agent | Associated clinical context | Special features |
|---|---|---|
| Methicillin-sensitive Staphylococcus aureus (MSSA) | Common community skin abscesses in people with no particular risk factors | Susceptible to penicillinase-resistant penicillins (cloxacillin) and to many common antibiotics |
| Community methicillin-resistant Staphylococcus aureus (C-MRSA) | Recurrent abscesses, intra-familial transmission, closed communities, people practicing contact sports | Increasingly prevalent in the community; treatment with trimethoprim-sulfamethoxazole, doxycycline or clindamycin, depending on antibiogram. |
| Streptococcus groups A, B, C, G | Abscesses often associated with extensive surrounding cellulitis, sometimes following a cutaneous wound | Betalactam-sensitive; risk of group A streptococcal necrotizing fasciitis |
| Anaerobic bacteria (Bacteroides, Peptostreptococcus) | Perianal abscesses, oral cavity abscesses, abscesses after human or animal bites | Pus often foul; treatment with amoxicillin-clavulanate or metronidazole in combination |
| Enterobacteriaceae (Escherichia coli, Klebsiella) | Perianal abscesses, abdominal subcutaneous abscesses, diabetics or immunocompromised persons | Variable resistance profile; antibiogram essential to guide treatment |
| Atypical mycobacteria | Abscesses after injections, tattoos, piercings, cosmetic or surgical procedures | Subacute or chronic course; resistance to usual antibiotics; mycobacterial culture required |
Clinical forms and specific locations
Cutaneous abscesses take a variety of clinical forms, depending on their anatomical location, mechanism of formation and the tissue involved. Some forms are given specific names in clinical practice.
| Clinical form | Location and mechanism | Clinical features |
|---|---|---|
| Furuncle | Deep infection of a hair follicle and perifollicular tissue, caused by Staphylococcus aureus | Painful inflammatory nodule centered on a hair, evolving towards a central purulent point; frequent localizations: nape of the neck, face, buttocks, thighs, armpits. |
| Anthrax (carboncycle) | Confluence of several adjacent boils forming an inflammatory placard with multiple drainage holes | Lesion more extensive and painful, fever frequent; diabetic or immunocompromised patients to be systematically investigated. |
| Hidrosadenitis suppurativa | Chronic inflammatory disease of the apocrine glands, affecting the armpits, groin, buttocks and breasts. | Recurrent abscesses, fistulas and fibrous scars evolving in flare-ups; specialized treatment with biologics (anti-TNF) in severe forms |
| Perianal abscess | Hermann et Desfosses anal gland infection, with formation of a perirectal collection | Severe anal pain, fever, perineal swelling; risk of anal fistula in absence of adequate drainage; proctological examination essential |
| Pilonidal sinus abscess | Infection of a pilonidal cyst located in the gluteal cleft, often maintained by ingrown hairs | Painful swelling above the coccyx; frequent recurrences without surgical excision of the fistulous tract |
| Abscess after injection | Infection secondary to subcutaneous or intramuscular injection (medications, injectable drugs) | Often polymicrobial; risk of atypical mycobacteria and Gram-negative bacteria; context of injection drug use to be investigated sensitively |
Clinical manifestations and diagnosis
The diagnosis of a skin abscess is primarily clinical. In the majority of cases, the physical examination can establish the diagnosis with certainty, and assess the need for further investigations.
- Localized swelling, painful, warm and erythematous, evolving over several days
- Fluctuation on palpation: sensation of fluid under tension, characteristic of a built-up collection, key clinical sign that the abscess is mature and drainable
- Maturation point: zone of softening or whitish transparency at the top of the lesion, corresponding to the zone of least skin resistance.
- Fever and chills in the case of large abscesses, immunocompromised patients or the onset of systemic dissemination
- Painful regional adenopathy indicating lymph node response to local infection
- Lymphangitis: red trail from lesion to regional lymph nodes, sign of extension along lymphatic vessels
- Surrounding cellulitis: diffuse, warm, painful redness of adjacent tissues, without fluctuation, which may spread rapidly
Further tests
In the majority of simple cutaneous abscesses in immunocompetent patients, no further investigations are required prior to drainage. However, certain clinical situations warrant additional investigations.
| Review | Indication | Clinical contribution |
|---|---|---|
| Pus culture (swabbing or aspiration) | Recurrent abscesses, suspected MRSA, immunocompromised, failure of initial antibiotic treatment | Identification of causative agent and antibiogram to adapt antibiotic therapy |
| Complete blood count (CBC) and CRP | Fever, signs of systemic diffusion, diabetic or immunocompromised patients, large abscesses | Assessing the systemic inflammatory response and detecting incipient sepsis |
| Blood cultures | High fever, chills, altered general condition, suspected bacteremia | Identification of bacteremia secondary to abscess; guide to systemic antibiotic therapy |
| Blood glucose and HbA1c | Recurrent or unusually severe abscesses in a patient with no known diagnosis of diabetes | Screening for unrecognized diabetes, frequently revealed by recurrent skin infections |
| Cutaneous ultrasound | Diagnostic doubt between abscess and cellulitis without collection, deep abscess difficult to delimit clinically | Confirmation of the presence of a fluid collection, drainage guidance for deep or poorly defined abscesses |
| CT or MRI | Suspicion of deep abscess or fascial necrosis, perianal abscess with pelvic extension, lack of response to drainage | Precise delineation of the extent of infection and planning of surgical management |
Treatment
Surgical incision and drainage is the gold standard for the treatment of skin abscesses, and remains the most effective procedure for evacuating purulent collections and enabling healing. Antibiotic therapy plays a complementary role in specific indications.
- Incision and drainage: local anaesthesia, clean incision over the point of maximum fluctuation, complete evacuation of pus, decompartmentalization of the cavity, saline irrigation; meching of the cavity is still practised, but its benefit on healing is debated by recent data.
- Antibiotic therapy adjuvant to drainage: indicated in cases of extensive surrounding cellulitis (greater than 2 cm around the abscess), fever or systemic signs, immunodepression, poorly controlled diabetes, facial abscess, very large abscess or suspected MRSA; usually lasts 5 to 7 days.
- Choice of antibiotic according to context: trimethoprim-sulfamethoxazole or doxycycline for coverage of community MRSA; cloxacillin or cefalexin if MRSA is unlikely; amoxicillin-clavulanate for bite abscesses or abscesses with an anaerobic component
- Local post-drainage care: regular dressings, second-line scar monitoring, gradual removal of packing if used
- Management of recurrences: systematic search for MRSA nasal carriage, decontamination with nasal mupirocin and chlorhexidine baths, screening for intra-familial contacts, correction of contributing factors.
Risk factors for recidivism and vulnerable populations
Some people have an increased susceptibility to recurrent skin abscesses. Identifying and correcting these factors is essential to reduce the frequency of episodes.
| Risk factor | Favoring mechanism | Corrective action |
|---|---|---|
| Poorly balanced diabetes | Hyperglycemia impairs neutrophil function and promotes bacterial growth | Optimizing glycemic control; screening for unrecognized diabetes in recurrent abscesses |
| Nasal carriage of Staphylococcus aureus | Chronic autoinoculation from the nasal reservoir to the skin through scratching or contact | Nasal decontamination with mupirocin 2 % twice a day for 5 days, repeated according to recurrence. |
| Immunodepression | Impaired cellular and humoral defense mechanisms against bacterial infections | Treatment of underlying cause; antibiotic prophylaxis in certain cases (profound neutropenia) |
| Obesity | Skin maceration in folds, impaired local lymphatic circulation, chronic systemic inflammation | Rigorous hygiene of skin folds, weight loss, use of absorbent powders in high-risk areas |
| Injection drug use | Direct inoculation of skin bacteria during injections, use of contaminated equipment, relative immunosuppression | Access to needle exchange and harm reduction programs, addictology care |
| Intra-family transmission of MRSA | Sharing towels, razors or clothing; direct skin contact between household members | Screening and simultaneous decontamination of all household members; hygiene education |
Consult at Clinique Omicron
Clinique Omicron has points of service in Quebec offering medical consultations for the management of skin infections, including clinical evaluation of abscesses, in-office drainage and prescription of appropriate treatments. The clinic's physicians and specialized nurse practitioners (SPNs) also monitor post-drainage wounds, look for contributing factors and refer patients to surgical or dermatological resources when the clinical situation so requires. To book an appointment at one of our Quebec locations, visit cliniqueomicron.ca or contact the clinic directly.
The content of this page is provided for informational purposes only and is not intended to replace the advice of a qualified healthcare professional. Consult a physician for any symptoms, questions or decisions you may have regarding your health.
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