Cutaneous Abscess

Cutaneous abscess is a collection of pus in the dermis and subcutis, ranging from a furuncle (infected hair follicle) and carbuncle (several adjacent furuncles) to deeper subcutaneous abscesses. Staphylococcus aureus is responsible in most; mixed anaerobic flora dominate in perineal, pilonidal and axillary lesions.

• Community acquired MRSA is common and spreads in households and institutions.
• Hidradenitis suppurativa and pilonidal disease are chronic abscess forming conditions.

Tender, erythematous, firm then fluctuant nodule, 1 to 10 cm, with pointing and spontaneous drainage; carbuncles have multiple draining sinuses, fever and malaise.

• Differential diagnosis: inflamed epidermoid cyst, hidradenitis suppurativa, pilonidal sinus, cellulitis, lymphadenitis, Bartholin abscess, mastitis, necrotising fasciitis, myiasis, mycetoma, cutaneous tuberculosis, deep fungal infection.
• Complications: spreading cellulitis, bacteraemia, osteomyelitis, septic arthritis, endocarditis, sepsis, scarring, recurrence, sinus tract formation.

Clinical, with bedside ultrasound for depth and loculation.

• Pus culture before antibiotics in recurrent disease, hospitalised, immunosuppressed or where MRSA is likely.
• Full blood count, CRP, glucose or HbA1c, HIV test.
• Imaging (CT or MRI) for deep, perianal or head and neck abscess.

Drainage cures most abscesses; antibiotics are adjunctive.

• Supportive: warm compresses until pointing, analgesia (paracetamol 1 g, ibuprofen 400 mg three times daily), dressing changes, hand hygiene, avoid squeezing, personal towels, washing linen at 60 degrees Celsius.
• Pharmacological: infiltrate lidocaine 1 percent (maximum 4.5 mg/kg; 7 mg/kg with adrenaline) before drainage. Add antibiotics for cellulitis over 5 cm, systemic signs, immunosuppression, diabetes, hand, face or genital abscess, and incomplete drainage: cotrimoxazole 960 mg twice daily or cefalexin 500 mg four times daily or flucloxacillin 500 mg four times daily for 5 to 7 days (clindamycin 300 to 450 mg three times daily or doxycycline 100 mg twice daily for MRSA). Severe or systemic: vancomycin 15 to 20 mg/kg IV every 12 hours. Recurrent disease: chlorhexidine 4 percent body wash for 5 to 7 days and intranasal mupirocin 2 percent twice daily for 5 days.
• Procedures: incision along relaxed skin tension lines, break loculations, irrigate with saline, pack lightly or place a loop drain (change at 24 to 48 hours); excision of cysts or pilonidal sinus after resolution; theatre drainage under anaesthesia for deep, large or perineal abscess.
• Special groups: pregnancy, flucloxacillin or cefalexin and avoid cotrimoxazole near term; children, weight based doses; HIV, culture and treat for MRSA; diabetic, treat early and admit when extensive.
• Red flags: systemic toxicity, crepitus, necrosis, rapidly spreading cellulitis, facial abscess near the eye or nose, perianal abscess, hand abscess with tendon sheath signs.
• Follow-up: review at 24 to 48 hours; repeat if fever persists; evaluate underlying disease in recurrent cases.