What are the symptoms and treatment of rectal cellulitis?

Rectal Cellulitis: Symptoms and Treatment

Clinical Presentation

Rectal cellulitis typically presents as part of perianal or perirectal infectious processes, most commonly manifesting with pain, swelling, erythema, and exquisite tenderness in the perianal region. 1

Key Symptoms to Identify

• Pain is the most common and prominent symptom, requiring differentiation from anal fissure, thrombosed hemorrhoids, levator spasm, sexually transmitted diseases, proctitis, and malignancy 1
• Low perianal abscesses (intersphincteric, perianal, and ischiorectal) present with visible swelling, cellulitis, and exquisite tenderness but typically have few systemic symptoms 1
• High abscesses (submucosal, supralevator) may have minimal local symptoms but significant systemic manifestations including fever and malaise 1
• Deeper infections can cause pain referred to the perineum, low back, or buttocks 1
• Additional symptoms may include increased stool frequency, urgency, tenesmus, pelvic discomfort, and occasionally rectal bleeding 1

Physical Examination Findings

• Erythema, warmth, and induration extending beyond any defined abscess borders indicates significant cellulitis requiring antibiotic therapy 1
• Tenderness on digital rectal examination or external inspection 1
• Assess for systemic signs: fever, tachycardia, or signs of sepsis 1

Treatment Algorithm

Immediate Assessment

Determine if this is simple cellulitis versus complex infection with abscess formation, as this fundamentally changes management. 1

1. If abscess is present or suspected: Prompt surgical drainage is mandatory and should not be delayed 1
2. If significant cellulitis without drainable collection: Proceed with antibiotic therapy 1
3. Evaluate for systemic signs: Fever, tachycardia, hypotension, or altered mental status requiring hospitalization 1

Antibiotic Selection

Empiric broad-spectrum antibiotic therapy must cover Gram-positive, Gram-negative, and anaerobic bacteria given the polymicrobial nature of perirectal infections. 1

Outpatient Oral Therapy (for mild cases without systemic symptoms):

• Amoxicillin-clavulanate provides comprehensive coverage of streptococci, staphylococci, and anaerobes 2, 3
• Alternative: Combination of a fluoroquinolone plus metronidazole for anaerobic coverage 1

Inpatient Parenteral Therapy (for moderate-severe cases or systemic symptoms):

• First-line: Broad-spectrum regimen such as piperacillin-tazobactam or a carbapenem 1
• Alternative: Ceftriaxone plus metronidazole for comprehensive coverage 1
• Severe penicillin allergy: Fluoroquinolone plus metronidazole, or clindamycin plus an aminoglycoside 1

MRSA Considerations

MRSA coverage should be added empirically if purulent drainage is present, there is history of MRSA colonization, or specific risk factors exist (injection drug use, prior MRSA infection, healthcare exposure). 1, 2

• Add vancomycin, daptomycin, or linezolid to the regimen 1
• Oral options for outpatient management: clindamycin, trimethoprim-sulfamethoxazole, or doxycycline 2, 3

Mandatory Indications for Antibiotic Therapy

Antibiotics are required when: 1

• Systemic signs of infection are present (fever, tachycardia, leukocytosis)
• Patient is immunocompromised
• Source control (drainage) is incomplete
• Significant cellulitis extends beyond abscess borders
• Deep tissue involvement or multiloculated extension exists

Surgical Management

Any identified abscess requires prompt surgical drainage—this is the definitive treatment and cannot be replaced by antibiotics alone. 1

• Drainage should be performed expeditiously to prevent expansion into adjacent spaces and systemic infection 1
• Multiple counter incisions are preferred over single long incisions to avoid step-off deformity and delayed healing 1
• Identify and address any fistula tract during drainage procedure 1

Treatment Duration and Follow-up

• Minimum 5-7 days of antibiotic therapy, with extension if not improving 2, 3
• Mandatory reassessment within 24-48 hours to ensure clinical improvement 4
• Failure to improve or progression despite appropriate therapy requires hospitalization, imaging, and possible surgical consultation 1

Critical Pitfalls to Avoid

The most dangerous error is treating a perirectal abscess with antibiotics alone without surgical drainage—this can lead to expansion into deeper spaces and life-threatening systemic infection. 1

• Do not delay surgical consultation when abscess is suspected clinically, even if not clearly fluctuant 1
• Inadequate anaerobic coverage is a common mistake given the polymicrobial nature of perirectal infections 1
• Failing to consider immunocompromised states (diabetes, HIV, malignancy) that require more aggressive management 1
• Not recognizing that deeper abscesses (supralevator) may have minimal local findings but significant systemic symptoms 1

Special Populations

Injection Drug Users

• Require special consideration with broader empiric coverage 1
• Evaluate for endocarditis if persistent systemic symptoms 1
• Rule out foreign bodies with radiography and vascular complications with duplex ultrasound 1
• Screen for HIV, HCV, and HBV 1

Inflammatory Bowel Disease Patients

• Perianal disease is common in Crohn's disease and requires consideration of underlying inflammatory process 1
• May require concomitant treatment of underlying IBD 1