Dermatology
A 74 year old woman is brought to the Emergency Department after her carers noted a red rash on her left calf. She has a past medical history of type 2 diabetes mellitus and peripheral arterial disease secondary to a smoking history. On examination you note the calf is red and hot to touch. Her observations are recorded as:
- Heart rate: 105 beats/minute
- Blood pressure: 139/67 mmHg
- Respiratory rate: 20 breaths/minute
- Temperature: 37.8°C
What is the most appropriate management for this patient?
Answer:
- Patients will likely require hospital admission for intravenous antibiotics (first line is intravenous flucloxacillin 500 mg - 2 g four times a day) if they:
- Have Class IV cellulitis
- Have Class III cellulitis
- Have Class II cellulitis
- Have severe or rapidly deteriorating cellulitis (for example extensive areas of skin)
- Are very young (under 1 year of age) or frail
- Are immunocompromised
- Have significant lymphoedema
- Have facial cellulitis (unless very mild)
- Have suspected orbital or periorbital cellulitis (refer to ophthalmology)
- Are not responding to oral treatment
Cellulitis and Erysipelas
Dermatology
Last Updated: 13th October 2023
Cellulitis is an acute bacterial infection of the dermis and subcutaneous tissue. The infected area is characterised by pain, warmth, swelling, and erythema. Blisters and bullae may form. Fever, malaise, nausea, and rigors may accompany or precede the skin changes. Cellulitis most commonly affects the lower limbs, but other areas, such as the upper limbs, face, ears, and trunk, can also be affected. The most common causative organisms are Streptococcus pyogenes or Staphylococcus aureus.
Risk factors
Most cases of cellulitis arise from bacterial infection through a break in the skin, for example from trauma (due to a bite, burn, or laceration), leg ulceration, maceration or fungal infection between the toes, or a concomitant skin disorder (such as atopic eczema).
Other risk factors for cellulitis include:
- Lymphoedema
- Leg oedema
- Venous insufficiency and history of venous surgery
- Obesity
- Pregnancy
Risk factors for either rapid progression of cellulitis or delayed response to treatment include:
- Conditions that predispose to infection, including diabetes mellitus, chronic liver or renal disease, immunocompromise, and neutropenia
- Chickenpox (varicella)
- Alcohol misuse
- Neuropathy
Clinical features
Cellulitis is more commonly seen in the lower limbs and usually affects one limb (bilateral leg cellulitis is very rare). Typical features include:
- An acute onset of red, painful, hot, swollen, and tender skin, that spreads rapidly
- Fever, malaise, nausea, shivering, and rigors — these may accompany or even precede skin changes
- There is usually an obvious skin break where the infecting organism may have entered, such as a wound, macerated skin, fungal skin infection, an ulcer, or a concomitant skin disorder (such as atopic eczema)
- There may be diffuse redness or a well-demarcated edge that can be marked with a pen in order to monitor progress
- Blisters and bullae may be seen.
- Occasionally, there may be inflamed regional lymph nodes or associated lymphangitis, characterised by the presence of red, linear streaks spreading proximally from the area of cellulitis.
- If swelling is significant, the skin surface may develop a peau d’orange appearance
- Severe cellulitis can lead to ulceration and more deep-seated tissue damage
If cellulitis is diagnosed, the severity can be categorised using the Eron classification system, to help guide management decisions.
- Class I — there are no signs of systemic toxicity and the person has no uncontrolled comorbidities
- Class II — the person is either systemically unwell or systemically well but with a comorbidity (for example peripheral arterial disease, chronic venous insufficiency, or morbid obesity) which may complicate or delay resolution of infection
- Class III — the person has significant systemic upset, such as acute confusion, tachycardia, tachypnoea, hypotension, or unstable comorbidities that may interfere with a response to treatment, or a limb-threatening infection due to vascular compromise
- Class IV — the person has sepsis or a severe life-threatening infection, such as necrotising fasciitis
Differential diagnosis
Common conditions that present with unilateral redness and/or swelling include:
- Deep venous thrombosis — characterised by pain and swelling of the calves
- Septic arthritis — involvement of the joint and disproportionate pain with joint movement
- Acute gout — swelling, redness, warmth, and pain on passive movement
- Ruptured Baker's cyst — may cause unilateral calf swelling
- Thrombophlebitis — venous inflammation with thrombus formation may cause redness, inflammation, and pain
- Cutaneous abscess — a hot, red, swollen and painful swelling
- Erysipelas — a form of cellulitis involving more superficial dermal structures distinguished clinically by raised and well demarcated borders
Chronic conditions (these are usually bilateral but if worse on one side, it may be difficult to exclude superimposed cellulitis) include:
- Varicose eczema/venous insufficiency — crusting, scaling, and itching
- Contact allergic dermatitis — can present acutely as erythematous, sore and tender areas of skin, sometimes with blisters
- Lipodermatosclerosis — a painful, red, tender, warm, hard, and sometimes scaly rash that occurs in the absence of significant systemic upset associated with venous insufficiency
- Cutaneous small vessel vasculitis — palpable purpura typically on the lower legs and ankles
- Lymphoedema — swelling that occurs as a result of excess accumulation of lymph due to inadequate drainage
- Oedema with blisters
- Panniculitis — inflammation of subcutaneous adipose tissue
Investigations
Investigations are not usually necessary but may be considered in certain cases, for example:
- A swab for culture — if there is an open wound, penetrating injury, drainage, or an obvious portal for microbial entry, exposure to water borne-organisms, an infection acquired outside the UK or in severe cellulitis
- Ultrasonography — for distinguishing nonpurulent cellulitis from cellulitis with underlying abscess and for identifying drainable fluid collection, particularly if the clinical assessment is indeterminate
- A skin biopsy — if there is doubt about the diagnosis and to help identify any unusual pathogens in people who are unresponsive to initial treatment
- White blood cell count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) — to detect acute inflammation
- Other relevant tests — to exclude differential diagnoses (such as deep vein thrombosis, septic arthritis, and acute gout)
Management
- Patients will likely require hospital admission for intravenous antibiotics (first line is intravenous flucloxacillin 500 mg - 2 g four times a day) if they:
- Have Class IV cellulitis
- Have Class III cellulitis
- Have Class II cellulitis
- Have severe or rapidly deteriorating cellulitis (for example extensive areas of skin)
- Are very young (under 1 year of age) or frail
- Are immunocompromised.
- Have significant lymphoedema
- Have facial cellulitis (unless very mild)
- Have suspected orbital or periorbital cellulitis (refer to ophthalmology)
- Are not responding to oral treatment
- People with Class I cellulitis can usually be treated at home with a high-dose oral antibiotics:
- Before treatment, draw around the extent of the infection with a permanent marker pen for future comparison and to track the spread of infection
- Advise the person to take analgesia as required, drink adequate fluids, elevate the leg for comfort and to relieve oedema, and seek immediate medical advice if antibiotics are not tolerated, the cellulitis becomes worse, or if systemic symptoms develop or worsen
- Manage breaks in the skin, for example, due to eczema, tinea pedis, or leg ulcers, which may become a portal of entry for organisms
- When prescribing oral antibiotics:
- For adults with Class I cellulitis: prescribe flucloxacillin 500–1000 mg four times daily for 5–7 days
- For adults with infection near the eyes or nose who do not require admission: prescribe co-amoxiclav 500/125 mg three times a day for 7 days
Complications
- Acute complications of cellulitis include:
- Deep-seated infection, such as:
- Necrotising fasciitis — a destructive and rapidly progressive soft tissue infection that involves the deep subcutaneous tissues and fascia (and occasionally muscles), which is characterised by extensive necrosis and gangrene of the skin and underlying structures; the presenting signs are usually non-specific (redness, swelling, and pyrexia) and the person is usually systemically very unwell with disproportionate pain
- Myositis — inflammation of muscle due to infection
- Sepsis
- Subcutaneous abscesses
- Post-streptococcal nephritis
- Deep-seated infection, such as:
- Chronic complications of cellulitis include:
- Persistent leg ulceration
- Lymphoedema (cellulitis causes lymphatic inflammation leading to permanent damage)
- Recurrent cellulitis
Erysipelas
Erysipelas is a bacterial skin infection involving the upper dermis that characteristically extends into the superficial cutaneous lymphatics. It is a tender, intensely erythematous, indurated plaque with a sharply demarcated border, reflecting its more superficial nature.
Historically, erysipelas occurred on the face, but cases today most often involve the legs. Unlike cellulitis, almost all erysipelas is caused by Group A beta-haemolytic streptococci (Streptococcus pyogenes).
Erysipelas should be treated in the same way as cellulitis.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
