The information – Cellulitis

The patient’s unmet needs (PUNs)

You are called out on a home visit to see a 72-year-old lady who, when she phoned, had told the receptionist: ‘It’s my cellulitis again’. The skin of her right leg has been painful, hot and red below the knee for a few days. She has a slight fever but is well in herself. ‘Why do I keep getting this?’ she asks. ‘And please be careful if you give me antibiotics – I’m allergic to penicillin and the one they usually try instead upsets my stomach.’

The doctor’s educational needs (DENs)

What causes cellulitis and which organisms are usually responsible?

Acute lower limb cellulitis is a spreading bacterial infection of the skin and subcutaneous tissues of the leg. It is most commonly caused by gram-positive bacteria Staphylococcus aureus and Streptococcus pyogenes. Less common organisms include Streptococcus pneumoniae, Haemophilus influenzae, gram-negative bacilli and anaerobes. Antibiotic-resistant strains of methicillin resistant Staphylococcus aureus (MRSA) are rarely a cause of cellulitis in the UK.

Which antibiotics should be used, and for how long? What should be prescribed in patients who are allergic to, or can’t tolerate, penicillins or macrolides?

The majority of cellulitis is treated empirically before organisms are isolated. As it is impractical to clinically distinguish between streptococcal and staphylococcal cellulitis, flucloxacillin is the antibiotic agent of choice, and it is normally given for seven to 14 days at a dose of 500mg qds. Penicillin V and amoxicillin are not recommended as the majority of staphylococcal organisms are resistant to them.

For patients with penicillin allergy, erythromycin 500mg qds is recommended. For those who cannot tolerate penicillins or macrolides, clindamycin 300mg qds is effective but carries a risk of antibiotic-related colitis. Cefalexin 500mg tds is another option – it is well tolerated but there is a risk of cross-reactivity in patients with true penicillin allergy.

Ceftriaxone 1g od can be given intravenously by practitioners with access to outpatient parental antimicrobial therapy services. For patients with suspected MRSA cellulitis, treatment options include doxycycline, minocycline and co-trimoxazole.

Which patients require IV antibiotics or admission?

The vast majority of patients with cellulitis are managed with oral antibiotics in the community by GPs. Indications for IV antibiotics or admission include:

• Patient is systemically well but has a comorbidity that may delay treatment resolution, for instance peripheral vascular disease, morbid obesity, immunosuppression or chronic venous insufficiency.

• Patient is systemically unwell, confused, tachycardic, hypotensive or tachypnoeic.

• Suspected septicaemia.

• Suspected necrotising fasciitis.

• Poor response to 48 hours of oral antibiotic therapy.

Varicose eczema can produce similar symptoms, but requires totally different treatment. How can this be distinguished from cellulitis?

The differential diagnosis of an acutely red, painful leg is wide and includes cellulitis, varicose eczema, deep vein thrombosis, acute lipodermatosclerosis (a sclerosing panniculitis due to venous insufficiency, although commonly seen as a chronic condition it may occur acutely with sudden onset erythema that may mimic cellulitis), acute oedema and erythema nodosum.

Features that suggest cellulitis:

• Pyrexia, malaise and systemic upset.

• A painful, hot, swollen, tender leg with spreading erythema.

• Raised CRP, ESR and white cell count.

• Unilateral disease.

• Presence of blistering, superficial haemorrhage, lymphangitis and lymphadenopathy.

Features that favour the diagnosis of varicose eczema:

• Bilateral disease.

• Clinical signs of venous incompetence.

• Pruritus.

• Dry, scaly skin.

• A systemically well, apyrexial patient.

Why do some patients seem to suffer repeated episodes? What can the GP do to prevent these? Is there a role for prophylactic antibiotics?

Up to 50% of patients who have suffered an episode of lower limb cellulitis will develop a recurrence at a later date. Although there is no research evidence, it seems sensible to address patients’ modifiable risk factors to reduce recurrent episodes. These include venous insufficiency, lymphoedema, peripheral arterial disease, diabetes, ulcers, eczema and tinea pedis. Fungal infections of the lower limb are a good example of an easily treatable significant risk factor for lower limb cellulitis.

The use of prophylactic antibiotics to prevent cellulitis recurrence is currently being investigated. So far the data from studies has shown benefit but this has not been statistically significant. Some guidelines recommend using long-term antibiotics in patients who have had two or more episodes of cellulitis at the same site – either penicillin V 250mg bd or erythromycin 250mg bd for one to two years.

Dr James Halpern is a consultant dermatologist at Walsall Healthcare NHS Trust and The Birmingham Skin Centre