Perineal Cellulitis

Perineal cellulitis is infection of the skin and subcutaneous tissue of the perineum, genitalia and perianal region, usually polymicrobial (streptococci, Staphylococcus aureus, Enterobacterales, anaerobes). It can progress to necrotising fasciitis of the perineum (Fournier gangrene), a surgical emergency.

• Risk factors: diabetes (including SGLT2 inhibitors), obesity, immunosuppression, HIV, alcohol dependence, incontinence, perianal abscess, urinary catheter, recent surgery, hidradenitis, pregnancy and childbirth.

Painful, warm, erythematous swelling of the perineum, scrotum, vulva or perianal skin, with fever, malaise and tenderness.

• Necrotising spread: pain out of proportion, blistering, dusky skin, crepitus, foul discharge, rapid progression, hypotension, confusion.
• Differential diagnosis: perianal and ischiorectal abscess, Bartholin abscess, epididymo orchitis, testicular torsion, hidradenitis, herpes, intertrigo, contact dermatitis, Fournier gangrene, Crohn disease, pressure sores.
• Complications: abscess, necrotising fasciitis, sepsis, septic shock, acute kidney injury, testicular loss, faecal or urinary diversion, death.

Clinical, with urgent imaging when severe.

• Full blood count, CRP, creatinine, glucose, lactate, blood cultures, wound cultures; urinalysis.
• Ultrasound (gas, collections, testicular perfusion); CT of pelvis with contrast for extent and source; do not delay surgery for imaging in suspected necrotising infection.
• HIV test and HbA1c.

Broad spectrum antibiotics, with urgent surgery for any necrotising infection.

• Supportive: admission, IV fluids, analgesia (morphine 2.5 to 5 mg IV titrated), glucose control with insulin, catheterisation if needed, nutritional support, wound care.
• Pharmacological: mild: amoxicillin clavulanate 625 mg three times daily for 7 to 10 days. Moderate or severe: ceftriaxone 2 g IV daily with metronidazole 500 mg IV every 8 hours (or piperacillin tazobactam 4.5 g IV every 6 hours). Suspected necrotising infection: piperacillin tazobactam 4.5 g IV every 6 hours or meropenem 1 g IV every 8 hours plus vancomycin 15 to 20 mg/kg IV every 12 hours and clindamycin 600 to 900 mg IV every 8 hours. Fluconazole 400 mg if fungal. Tetanus toxoid if indicated.
• Procedures: urgent wide surgical debridement of all necrotic tissue and repeated looks within 24 hours; drainage of abscess; faecal diversion (colostomy) and suprapubic catheter if needed; hyperbaric oxygen where available; reconstruction after healing.
• Special groups: pregnancy and postpartum, give amoxicillin clavulanate or ceftriaxone with metronidazole, check vancomycin levels if it is used and arrange obstetric review; diabetes, aggressive control; HIV, antiretroviral therapy; elderly, early intensive care; children, weight based doses.
• Red flags: pain out of proportion, crepitus, skin necrosis, bullae, hypotension, rapidly progressing erythema, tachycardia, lactate over 2 mmol/L, diabetic ketoacidosis.
• Follow-up: daily wound review; reconstructive surgery; reassessment of diabetes control and SGLT2 inhibitor use; review at 2 weeks and 6 weeks.