What is the recommended management, including antibiotic therapy and surgical treatment, for an inflamed (infected) epidermal cyst?

Management of Inflamed Epidermal Cysts

Incision and drainage is the definitive treatment for inflamed epidermal cysts, and antibiotics should only be added when specific systemic infection criteria are present. 1, 2, 3

Primary Treatment: Incision and Drainage

The cornerstone of management is adequate surgical drainage, not antibiotics. 1, 2, 3

Critical Technical Steps

• Perform an incision large enough to permit complete evacuation of all cheesy keratinous material and pus 1, 2
• Probe the cavity thoroughly to break up all loculations and septations—this is the single most critical step to prevent treatment failure 1, 2, 3
• Ensure total evacuation of all cyst contents; incomplete drainage is the most common cause of persistent discharge and recurrence 1, 2, 3
• Cover with a simple dry dressing only—do not pack the wound, as packing increases pain without improving healing outcomes 1, 2, 3

Why Drainage Works

The inflammation in epidermal cysts results from rupture of the cyst wall with extrusion of keratin into the dermis, not from primary bacterial infection. 1 Both inflamed and uninflamed cysts contain normal skin flora, and research shows that 47% of mild inflamed cysts culture negative or grow only normal flora. 4

When to Add Antibiotics

Antibiotics are unnecessary for most inflamed epidermal cysts and should be reserved for patients meeting specific systemic criteria. 1, 2, 3

Specific Indications for Antibiotic Therapy

Add systemic antibiotics only when any of the following are present:

• Temperature >38°C or <36°C 1, 2, 3
• Heart rate >90 beats/min 1, 2, 3
• Respiratory rate >24 breaths/min 1, 2, 3
• White blood cell count >12,000 cells/µL or <4,000 cells/µL 1, 2, 3
• Extensive surrounding cellulitis with erythema extending >5 cm beyond wound margins with induration 1, 2, 3
• Severely impaired host defenses or immunocompromised state 1, 2, 3
• Multiple lesions or cutaneous gangrene 1

Antibiotic Selection (When Indicated)

Target Staphylococcus aureus, the most common pathogen: 2, 3

For Methicillin-Susceptible S. aureus (MSSA):

• Cephalexin 500 mg every 6 hours orally 1, 3
• Cefazolin 1 g every 8 hours IV 1, 3

For Suspected or Confirmed MRSA:

• Vancomycin 15-20 mg/kg every 8-12 hours IV 1, 3
• Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily orally 1, 3
• Doxycycline 100 mg twice daily orally 1, 3
• Clindamycin 300-450 mg four times daily orally (only if local MRSA resistance <10%) 1, 3

Duration: 5-7 days, adjusted by clinical response 1, 3

Microbiologic Testing

Do not routinely obtain Gram stain and culture from inflamed epidermal cysts. 1, 2, 3, 4 Reserve cultures only for:

• Patients with systemic infection signs 1, 2, 3
• Treatment failure 1, 2, 3
• Immunocompromised patients 1, 2, 3

Management of Persistent Drainage or Treatment Failure

Most wounds heal within 2-3 weeks; persistent drainage beyond this timeframe indicates inadequate initial treatment requiring re-drainage. 1, 2, 3

Re-Drainage Protocol:

• Re-open the incision and ensure complete evacuation of all remaining contents 1, 2, 3
• Probe the cavity again to disrupt any residual loculations or septations 1, 2, 3
• Search for retained foreign material if recurrences continue at the same site 1, 2, 3
• Cover with a dry dressing; do not pack the wound 1, 2, 3

Definitive Treatment for Recurrent Infection

For patients with recurrent infection at the same location, perform complete excision of the cyst and its wall after acute inflammation has resolved. 1, 2, 3 One-stage excision during acute inflammation is an alternative approach that decreases antibiotic exposure and reduces morbidity compared to conventional staged treatment. 5

Critical Pitfalls to Avoid

• Never prescribe antibiotics without adequate drainage—antibiotics alone will fail because the problem is mechanical, not infectious 1, 3
• Never close the wound without adequate drainage—this guarantees recurrent infection 2, 3
• Never pack the wound—it causes more pain without improving healing 1, 2, 3
• Never assume ongoing drainage beyond 2-3 weeks is normal healing—this signals inadequate initial treatment 1, 3
• Never routinely prescribe antibiotics in the absence of systemic infection criteria—nearly half of mild inflamed cysts are culture-negative 1, 2, 3, 4