Is antibiotic therapy indicated for a patient with an epidermal inclusion cyst on the upper back in the absence of signs of infection?

Antibiotic Therapy for Epidermal Inclusion Cysts

Antibiotics are not indicated for an epidermal inclusion cyst on the upper back unless there are clear signs of bacterial infection with systemic inflammatory response or extensive surrounding cellulitis. 1

Primary Treatment Principle

The cornerstone of management for epidermal inclusion cysts is incision and drainage when indicated, not antibiotic therapy. 1, 2

• Incision and drainage is the primary treatment for simple abscesses or boils, and antibiotics should not be used for simple abscesses or boils. 1
• Studies of subcutaneous abscesses found no benefit for antibiotic therapy when combined with drainage. 1
• The single published trial of antibiotic administration for surgical site infections found no clinical benefit associated with this treatment. 1

When Antibiotics Are NOT Needed

If there is minimal surrounding evidence of invasive infection (<5 cm of erythema and induration) and minimal systemic signs of infection (temperature <38.5°C and pulse rate <100 beats/min), antibiotics are unnecessary. 1

• Superficial incisional infections that have been opened can usually be managed without antibiotics. 1
• Because incision and drainage of superficial abscesses rarely causes bacteremia, antibiotics are not needed. 1
• Almost half (47%) of mild inflamed epidermal inclusion cysts cultured will not grow pathogenic bacteria. 3

When Antibiotics ARE Indicated

Antibiotics should only be prescribed when specific criteria are met: 1, 2

• Systemic inflammatory response: Temperature >38.5°C or <36°C, tachycardia >90 bpm, tachypnea >24 breaths/min, or WBC >12,000 or <4,000 cells/µL 1, 2
• Extensive surrounding cellulitis: >5 cm of erythema with induration 1, 4
• Signs of organ failure: Hypotension, oliguria, decreased mental alertness 1
• Immunocompromised patients or markedly impaired host defenses 1, 2

Antibiotic Selection (When Indicated)

If antibiotics are deemed necessary based on the above criteria, they should be active against Staphylococcus aureus, which is the most common pathogen. 2

• For clean procedures not entering the intestinal or genital tracts, S. aureus (including MRSA) and streptococcal species are the most common organisms. 1
• In one study of inflamed epidermal inclusion cysts, when bacteria grew, methicillin-resistant Staphylococcus aureus (8%), Staphylococcus lugdunensis (5%), and methicillin-sensitive Staphylococcus aureus (13%) predominated. 3

Understanding the Pathophysiology

The inflammation in epidermal inclusion cysts typically occurs as a reaction to rupture of the cyst wall and extrusion of its contents into the dermis, rather than as a primary infectious complication. 2

• This explains why many inflamed cysts are culture-negative and do not require antibiotics. 3
• Gram stain and culture of pus from inflamed epidermoid cysts are not recommended as routine practice. 2

Common Pitfalls to Avoid

• Do not routinely prescribe antibiotics for neck masses or skin masses unless there are signs and symptoms of bacterial infection. 1
• Do not assume inflammation equals infection requiring antibiotics. 2, 3
• Do not prescribe antibiotics without addressing the mechanical problem through adequate drainage. 4
• Antibiotics alone without adequate drainage will fail. 4

Proper Management Algorithm

1. Assess for systemic signs: Check temperature, heart rate, respiratory rate, mental status 1, 2
2. Measure surrounding erythema: If <5 cm without induration, antibiotics not needed 1
3. Perform incision and drainage if fluctuant or draining 1, 2
4. Cover with dry sterile dressing (do not pack with gauze as it causes more pain without improving healing) 4, 2
5. Reserve antibiotics only for patients meeting the specific criteria outlined above 1, 2