Cellulitis : Causes | Symptoms | Treatment

Definition

Cellulitis is acute inflammation of the skin and deeper subcutaneous tissue underneath due to infection. It is always caused by bacterial infection.

When left untreated it can have serious complications like fasciitis, limb ischemia and septicaemia. Treatment with antibiotics results in good prognosis.

Erysipelas is similar to cellulitis in that it is also a skin infection but is more superficial than cellulitis.

Bacteria enters the skin when the skin barrier has been broken such as after a small injury. This explains why cellulitis is common in lower limbs and hands or toes.

Paronychia is a bacterial infection of the area around finger nail or toenail. It is usually localized but can complicate into cellulitis when the infection spreads to the rest of the finger.

Causes of Cellulitis

Most common bacteria associated with cellulitis are:

• Staphylococcus Aureus and Methicillin Resistant S. Aureus (MRSA)
• Group A ß-Hemolytic Streptococcus such as Streptococcus Pyogenes
• Streptococcus agalactiae (group B streptococci)
• Hemophilus infuenzae
• E.coli ( around perianal area)
• Mycobacterium Tuberculosis (in immunocompromised)

Bites from animals such as cats, dogs and even humans can lead to infection with uncommon bacteria such as:

• Eikenella corrodens (from humans)
• Capnocytophaga canimorsus (from dogs)
• Pasteurella multocida (from cats)
• Streptobacillus moniliformis (from rats)

Cellulitis Risk Factors

• Open wound especially on legs and upper limbs
• HIV/AIDS
• Diabetes Mellitus
• Obesity
• Poor hygiene
• Illicit IV drug  use
• Wound contamination
• Extremes of age (very young and  elderly population)

Symptoms and Signs

Symptoms

Swelling of the affected limb or hand, accompanied by pain. There may be localized redness, warmth and orange peel like skin.

Systemic symptoms of infection are also common in cellulitis. These include fever, headache, poor appetite, nausea and vomiting.

Signs

• Signs of infection such as Erythema, Oedema, Tenderness and Warmth
• Peau d’Orange skin: orange peel like appearance 
• Bullae which contain serous fluid
• Pyrexia especially in children, defined as skin temperature >38°C.
• Pustules and vesicles may be present.

Cellulitis may be mistaken for erysipelas due to the similarity in their signs and symptoms. The table below illustrates key differences between erysipelas and cellulitis.

Cellulitis Diagnosis

Cellulitis diagnosis is clinical based on history and physical examination. It is important to rule out Deep Venous Thrombosis (DVT) especially if cellulitis is on the lower limb.

Blood Tests

• C-reactive Protein (CRP) and Erythrocyte sedimentation rate (ESR) are elevated indicating inflammation.
• Full Blood Count (FBC) shows elevated white cell count especially in severe infections and in children. Platelet count may also be elevated.
• D-Dimers are done to rule out DVT. They are significantly high in DVT while they may be slightly raised or normal in Cellulitis.

Microscopy, Culture & Sensitivity (MC&S)

If cellulitis has an open wound, a bullae or vesicle, do pus swab for MC&S while empirically treating for common bugs.

Blood culture may show bacteremia indicating septicemia. It is particularly important in immunocompromised patients, children and patients who are not responding to antibiotics.

Excess pus can be collected on a sputum jar and sent to the lab as well.

Treatment of Cellulitis

Management of cellulitis can be approached in the following way:

1. Empiric antibiotics while waiting for MC&S and when there’s no place to collect specimen.
2. Analgesia and NSAIDs
3. Wound management

Decision to admit depends on the extent of the infection. Most patients benefit from admission and IV antibiotics.

Use the following antibiotics for treating cellulitis as they are effective against many skin infections and penetrate the skin well:

• Cloxacillin 1g IV 6 hourly for 5 to 10 days. OR
• Cefazolin 1g IV 8 hourly. OR
• Flucloxacillin 500mg oral 6 hourly for 10 days. OR
• Cephalexin 500mg oral 6 hourly for 5 to 10 days. OR
• Dicloxacillin 250mg oral 6 hourly for 5 to 10 days.

In the case of mammalian bite use Amoxicillin/Clavulanic Acid 875/125 oral 12 hourly for 5 to 10 days to treat cellulitis.

When culture results come back, use appropriate antibiotics that are shown to be sensitive to the cultured bug.

For Fever and inflammation, the give the following combination of antipyretics and NSAIDs. Remember, NSAIDs are not good for patients Peptic Ulcer:

• Paracetamol (acetaminophen) 1g oral 6 hourly prn. AND
• Ibuprofen 400mg oral 8 hourly after meals. OR
• Naproxen 250mg oral 8 hourly after meals.

Pressure bandage and limb elevation helps to reduce swelling. Do Incision and drainage if there is pus collection and any open wound should be dressed daily with antibiotic-containing dressing.

Complications

• Septicemia
• Necrotizing fasciitis
• Contractures
• Amputation