What is the appropriate management for an infected sebaceous (epidermoid) cyst?

Treatment for an Infected Sebaceous Cyst

Perform incision and drainage with thorough evacuation of all cyst contents and probing of the cavity to break up loculations—this is the definitive acute treatment, and antibiotics are reserved only for patients with systemic signs of infection or extensive cellulitis. 1, 2

Immediate Management: Incision and Drainage Technique

The cornerstone of treatment is proper surgical drainage, not antibiotics. 1, 2 Execute the following steps:

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

Understanding the Pathophysiology

• Inflammation arises from rupture of the cyst wall with extrusion of keratin into the dermis, not from primary bacterial infection; both inflamed and uninflamed cysts contain normal skin flora. 1
• This explains why antibiotics alone without adequate drainage will fail. 3

When to Use Systemic Antibiotics

Reserve antibiotics strictly for patients meeting ANY of these criteria:

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

If antibiotics are indicated, use the following regimens:

• For MSSA: Oral cephalexin 500 mg every 6 hours or IV cefazolin 1 g every 8 hours 1
• For suspected/confirmed MRSA:
  • IV vancomycin 15–20 mg/kg every 8–12 hours 1
  • Oral trimethoprim-sulfamethoxazole 1–2 double-strength tablets twice daily 1
  • Oral doxycycline 100 mg twice daily 1
  • Oral clindamycin 300–450 mg four times daily (only if local MRSA resistance <10%) 1
• Duration: 5–7 days, adjusted by clinical response 1

Microbiologic Testing

• Do not routinely obtain Gram stain and culture of inflamed epidermoid cysts. 1, 2
• Obtain cultures only when systemic infection signs, treatment failure, or immunocompromise are present. 1

Managing Persistent Drainage or Treatment Failure

Normal healing occurs within 2–3 weeks; drainage beyond this indicates inadequate initial management. 1, 3

If drainage persists beyond 2–3 weeks or worsens:

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

Critical Pitfalls to Avoid

• Do not prescribe antibiotics without addressing the mechanical problem—antibiotics alone without adequate drainage will fail. 3
• Do not assume ongoing drainage is normal healing beyond 2–3 weeks; this signals inadequate initial treatment. 3
• Do not close the wound without ensuring complete drainage—this leads to recurrent infection. 3, 2
• Do not pack the wound unnecessarily—this increases pain without improving outcomes. 1, 3, 2