What is the appropriate treatment for an infected intradermal cyst?

Treatment of Infected Intradermal Cyst

Incision and drainage is the primary and most important treatment for an infected intradermal (epidermal inclusion) cyst, and antibiotics are typically unnecessary unless systemic signs of infection or extensive surrounding cellulitis are present. 1, 2

Primary Treatment: Incision and Drainage

The cornerstone of management is surgical drainage with complete evacuation of infected material. 1, 2

• Open the cyst completely and evacuate all purulent contents and cyst material 1, 2
• Probe the cavity thoroughly to break up any loculations or septations that may prevent complete drainage 3, 2
• Cover with a simple dry sterile dressing after drainage—this is the easiest and most effective wound management 2
• Do not pack the wound with gauze—packing causes more pain without improving healing outcomes 3, 2
• Allow the wound to heal by secondary intention with regular dressing changes 1

When Antibiotics Are NOT Needed

Most infected epidermal cysts do not require systemic antibiotics if properly drained. 1, 2, 4

• Antibiotics are unnecessary when erythema is <5 cm from the wound margin and the patient lacks systemic signs of infection 1
• Specifically, antibiotics are not needed if: temperature <38.5°C, heart rate <110 beats/minute, and white blood cell count <12,000 cells/µL 1
• Studies show that 47% of inflamed epidermal cysts have negative cultures or only normal flora 4
• The inflammation often represents a sterile foreign body reaction to cyst contents rather than true bacterial infection 2

When Antibiotics ARE Indicated

Antibiotics should be added only in specific circumstances: 1, 2

• Temperature >38.5°C or heart rate >110 beats/minute 1
• Erythema extending >5 cm beyond the wound margins with induration 1
• Systemic signs of infection: temperature >38°C or <36°C, tachycardia >90 bpm, tachypnea >24 breaths/min, or WBC >12,000 or <4,000 cells/µL 2
• Immunocompromised patients or those with markedly impaired host defenses 3, 2

When antibiotics are needed, use a short course (24-48 hours) of agents active against Staphylococcus aureus, the most common pathogen. 1, 2

Culture Considerations

• Routine Gram stain and culture are NOT recommended for inflamed epidermal cysts 2
• Culture may be considered if antibiotics are required or if the patient fails to respond to drainage alone 4
• Common pathogens when present include methicillin-resistant S. aureus (8%), methicillin-sensitive S. aureus (13%), and anaerobes like Finegoldia magna (9.3%) 4

Management of Treatment Failure

If drainage persists beyond 2-3 weeks or infection recurs: 3

• Re-open the incision and ensure complete evacuation of all contents 3
• Probe thoroughly to break up any remaining loculations 3
• Search for retained foreign material or cyst wall remnants at recurrent sites 3, 2
• Inadequate initial drainage is the most common cause of treatment failure 3

Definitive Management

• Once acute inflammation resolves, consider complete excision of the cyst with its entire wall to prevent recurrence 2
• This is particularly important for cysts with repeated infections at the same site 2

Critical Pitfalls to Avoid

• Do not prescribe antibiotics without adequate drainage—antibiotics alone will fail without mechanical evacuation of infected material 3
• Do not assume ongoing drainage is normal healing—most wounds should heal within 2-3 weeks 3
• Do not close the wound primarily—this leads to recurrent infection 3, 2
• Do not pack the wound unnecessarily—this increases pain without benefit 3, 2