Lower Limb Cellulitis

Lower limb cellulitis is acute spreading bacterial infection of the dermis and subcutaneous tissue of the leg, mostly caused by beta haemolytic streptococci and Staphylococcus aureus. It is the commonest form of cellulitis and a leading reason for admission.

• Entry points: tinea pedis, interdigital fissures, ulcers, wounds, insect bites, eczema, lymphoedema, venous insufficiency, obesity.
• Risk factors: diabetes, previous cellulitis (recurrence in 20 to 30 percent), peripheral oedema, immunosuppression, injection drug use, saphenous vein harvest.

Unilateral warm, red, swollen, tender, poorly demarcated area of the leg or foot, with fever, rigors and lymphangitis; blisters or bullae may form.

• Erysipelas: sharply demarcated raised margin and abrupt onset.
• Differential diagnosis: deep vein thrombosis, venous stasis dermatitis, contact dermatitis, gout, acute lipodermatosclerosis, necrotising fasciitis, erythema nodosum, septic arthritis, ruptured Baker cyst, drug reaction, insect bite, lymphoedema.
• Complications: abscess, necrotising fasciitis, bacteraemia and sepsis, lymphangitis, osteomyelitis, septic arthritis, recurrent infection with chronic lymphoedema, post streptococcal glomerulonephritis, thrombophlebitis, toxic shock syndrome.

Clinical.

• Full blood count, CRP, creatinine, glucose; blood cultures when febrile or severe (positive in under 10 percent); swab of exudate or abscess.
• Duplex ultrasound if deep vein thrombosis is suspected; ultrasound for abscess; MRI for suspected osteomyelitis or necrotising infection.
• Examine the feet for tinea and portal of entry.

Antibiotics against streptococci with staphylococcal cover, leg elevation and treatment of the portal of entry.

• Supportive: elevate the leg, rest, analgesia (paracetamol 1 g, ibuprofen 400 mg if renal function allows), mark the margin of erythema, gentle compression once acute inflammation settles, emollients, treat oedema.
• Pharmacological: flucloxacillin 500 mg to 1 g four times daily for 5 to 7 days (extend to 10 to 14 days if slow response); phenoxymethylpenicillin 500 mg four times daily for non purulent erysipelas; penicillin allergy: clindamycin 300 to 450 mg three times daily, or doxycycline 100 mg twice daily. Severe or systemic: benzylpenicillin 1.2 to 2.4 g IV every 6 hours with flucloxacillin 1 to 2 g IV every 6 hours; MRSA risk: vancomycin 15 to 20 mg/kg IV every 12 hours, or cotrimoxazole 960 mg twice daily plus penicillin. Recurrent cellulitis (two or more episodes a year): benzathine benzylpenicillin 1.2 million units IM every 3 to 4 weeks or phenoxymethylpenicillin 250 to 500 mg twice daily for at least 6 to 12 months. Tinea pedis: terbinafine 1 percent cream twice daily for 2 weeks.
• Procedures: drainage of abscess; debridement of necrotic tissue; compression therapy after resolution for chronic oedema.
• Special groups: pregnancy, flucloxacillin or penicillin V; diabetes with an ulcer, add cover for gram negative bacteria and anaerobes with amoxicillin clavulanate 625 mg three times daily and check perfusion; children, flucloxacillin 12.5 to 25 mg/kg four times daily; elderly, monitor renal function and falls.
• Red flags: pain out of proportion, rapid spread, bullae with dusky skin, crepitus, hypotension, confusion, lactate over 2 mmol/L, no improvement at 48 hours.
• Follow-up: review at 48 to 72 hours; treat tinea and oedema; assess for recurrence and consider prophylaxis.