Makindo Medical Notes

Related Subjects: |Cellulitis |Impetigo |Pyoderma gangrenosum |Pemphigus Vulgaris |Toxic Epidermal Necrolysis |Stevens-Johnson Syndrome |Necrotising fasciitis |Gas Gangrene (Clostridium perfringens) |Anatomy of Skin |Skin Pathology and lesions |Skin and soft tissue and bone infections

Cellulitis is a common skin infection that affects the subcutaneous tissues, often caused by Streptococcus pyogenes or Staphylococcus aureus. Early recognition and prompt treatment are essential to prevent complications. Bilateral red legs is common. Red and normal or cool legs is unlikely to be cellulitis.

About Cellulitis

• A bacterial infection affecting the skin and underlying tissues, typically presenting as redness, swelling, and tenderness.
• While cellulitis is rarely life-threatening, untreated or severe cases can lead to systemic complications.
• Most commonly caused by *Streptococcus pyogenes* or *Staphylococcus aureus*.
• Usually affects the legs, but it can occur anywhere on the body.

Risk Factors

• Skin trauma, including cuts, bites, burns, or surgical wounds.
• Underlying conditions such as lymphoedema, tinea pedis, and venous insufficiency.
• Immune system suppression, obesity, or chronic leg oedema.
• Diabetes and peripheral vascular disease are significant risk factors for severe infection.

Clinical Features

• Red, erythematous, swollen, and tender skin, often without pus formation.
• Commonly affects the lower legs but may appear on the arms, face, or other areas.
• Fluctuating warmth, swelling, and discomfort at the site of infection.
• Occasionally accompanied by systemic symptoms such as fever (pyrexia).
• Inspect for possible entry points, such as skin breaks between the toes or around existing wounds.
• Mark the edges of erythema with a pen to monitor progression.

Differential Diagnosis

• Deep vein thrombosis (DVT), especially if there is leg swelling and a history of recent immobilization.
• Lymphangitis, abscess, venous ulcers, and cellulitis mimicking dermatitis.
• Necrotizing fasciitis, gas gangrene, or osteomyelitis are more severe conditions to rule out.

Severe Cellulitis Indicators

• Rapid spread of the lesion, high fever (>38°C), or signs of sepsis (hypotension, tachycardia).
• Facial or hand involvement, which requires urgent management.
• Failure to respond to adequate doses of oral antibiotics.
• Risk factors such as asplenia, neutropenia, cirrhosis, or immune suppression.
• Patients with cardiac or renal failure or pre-existing oedema may experience complications.

Cellulitis Classification

Common Pathogens

• *Staphylococcus aureus* (most common cause).
• Beta-hemolytic streptococci, particularly group A.
• Anaerobic organisms, especially in patients with diabetes or ischaemic limbs.

Patients at Higher Risk

• Individuals with diabetes, especially diabetic foot infections.
• Immunocompromised patients (e.g., on chemotherapy, HIV-positive individuals).
• Patients with peripheral vascular disease or chronic venous insufficiency.

Diagnostic Approach

• FBC: Elevated white cell count (WCC), ESR, and CRP.
• U&E and Glucose: Check glucose levels to screen for undiagnosed diabetes.
• Blood Cultures: For patients who are systemically unwell or pyrexial.
• Imaging: X-ray if osteomyelitis is suspected or if there’s concern for deep tissue involvement.

Management of Cellulitis

• If the patient is systemically unwell, obtain blood cultures and swabs from any visible pus or wound openings.
• For mild-to-moderate cellulitis, treat with empirical antibiotics. The combination of benzyl penicillin (1.2g qds IV) and flucloxacillin (1g qds IV) is commonly used until clinical improvement occurs.
• For penicillin allergies, use teicoplanin (400mg IV once daily after three loading doses).
• In severe cases or diabetic foot infections, use co-amoxiclav (1.2g tds IV) or clindamycin (if penicillin allergy is present).
• Consider urgent surgical consultation if there is suspected necrotizing fasciitis or deep abscesses requiring drainage.
• In cases of superficial cellulitis, cryotherapy, or curettage may be used for more localized, uncomplicated infections.
• Follow-up care for patients with diabetes and chronic wounds requires close monitoring by diabetes podiatrists and microbiologists.