Cellulitis

Cellulitis Classification and external resources
Infected left shin
ICD-10	L03.
ICD-9	682.9
DiseasesDB	29806
eMedicine	med/310  emerg/88 derm/464
MeSH	D002481

Cellulitis is an infection of the deep subcutaneous tissue of the skin. Cellulitis can be caused by normal skin flora or by exogenous bacteria, and often occurs where the skin has previously been broken: cracks in the skin, cuts, blisters, burns, insect bites, surgical wounds, or sites of intravenous catheter insertion. Skin on the face or lower legs is most commonly affected by this infection, though cellulitis can occur on any part of the body. The mainstay of therapy remains treatment with appropriate antibiotics.

Erysipelas is the term used for a more superficial infection of the dermis and upper subcutaneous layer that presents clinically with a well defined edge. Erysipelas and cellulitis often coexist, so it is often difficult to make a distinction between the two.

Cellulitis is unrelated to cellulite, a cosmetic condition featuring dimpling of the skin.

Symptoms

Cellulitis in a Limb showing typical red streaks and swelling

Early symptoms may include fever, headache, nausea, or itching and early signs of redness on the affected area.

Cellulitis is characterized by redness, swelling, warmth, and pain or tenderness. Cellulitis frequently occurs on exposed areas of the body such as the arms, legs, feet, and face. Other symptoms can include fever or chills and headaches. In advanced cases of cellulitis, red streaks (sometimes described as 'fingers') may be seen traveling up the affected area. The swelling can spread rapidly.

Causes

Infected left shin in comparison to shin with no sign of symptoms

Cellulitis is caused by a type of bacteria entering by way of a break in the skin. This break need not be visible. Group A Streptococcus and Staphylococcus are the most common of these bacteria, which are part of the normal flora of the skin but cause no actual infection until the skin is broken. Predisposing conditions for cellulitis include insect bite, blistering, animal bite, tattoos, pruritic skin rash, recent surgery, athlete's foot, dry skin, eczema, injecting drugs (especially subcutaneous or intramuscular injection or where an attempted IV injection "misses" or blows the vein); plus burns and boils, though there is debate as to whether minor foot lesions contribute and also morbidly obese people can experience it.

The photos shown here of Cellulitis are more severe cases than what can be spotted typically at earlier stages. Usually the itch and/or rash appears but shortly after vanishes leaving only a small mark which is commonly ignored.

The appearance of the skin will help a doctor make a diagnosis. The doctor may also suggest blood tests, a wound culture or other tests to help rule out a blood clot deep in the veins of the legs. Cellulitis in the lower leg is characterized by signs and symptoms that may be similar to those of a clot occurring deep in the veins, such as warmth, pain and swelling.

This reddened skin or rash may signal a deeper, more serious infection of the inner layers of skin. Once below the skin, the bacteria can spread rapidly, entering the lymph nodes and the bloodstream and spreading throughout the body.

In rare cases, the infection can spread to the deep layer of tissue called the fascial lining. Necrotizing fasciitis, also called by the media "flesh-eating bacteria", is an example of a deep-layer infection. It represents an extreme medical emergency.

Risk factors

The elderly and those with weakened immune systems are especially vulnerable to contracting cellulitis. Diabetics are more susceptible to cellulitis than the general population because of impairment of the immune system; they are especially prone to cellulitis in the feet because the disease causes impairment of blood circulation in the legs leading to foot ulcers. Poor control of blood glucose levels allows bacteria to grow more rapidly in the affected tissue and facilitates rapid progression if the infection enters the bloodstream. Neural degeneration in diabetes means these ulcers may not be painful and thus often become infected.

Immunosuppressive drugs, HIV, and other illnesses or infections that weaken the immune system are also factors that make infection more likely. Chickenpox and shingles often result in blisters which break, providing a gap in the skin through which bacteria can enter. Lymphedema, which causes swelling on the arms and/or legs, can also put an individual at risk.

Diseases that affect blood circulation in the legs and feet, such as chronic venous insufficiency and varicose veins, are also risk factors for cellulitis.

Cellulitis is also extremely prevalent amongst dense populations sharing hygiene facilities and common living quarters, such as military installations, college dormitories, and homeless shelters.

Diagnosis

Cellulitis is most often a clinical diagnosis, and local cultures do not always identify the causative organism. Blood cultures usually are positive only if the patient develops generalised sepsis. Conditions that may resemble cellulitis include deep vein thrombosis, which can be diagnosed with a compression leg ultrasound, and stasis dermatitis, which is inflammation of the skin from poor blood flow.

There have been many cases where Lyme disease has been misdiagnosed as Staph- or Strep- induced cellulitis. Because the characteristic bullseye rash does not always appear in patients infected with Lyme disease, the similar set of symptoms may be misdiagnosed as cellulitis. Standard treatments for cellulitis are not sufficient for curing Lyme disease. The only way to rule out Lyme disease is with a blood test, which is recommended during warm months in areas where Lyme is endemic^[1].

Incubation

Cellulitis can develop in as little as twenty-four hours or can take days to develop.

Duration

In many cases, cellulitis takes less than a week to disappear with antibiotic therapy. However, it can take months to resolve completely in more serious cases, and can result in severe debility or even death if untreated especially when found in women. If it is not properly cured it may appear to improve but can resurface again even after months and years.

Treatment

Treatment consists of resting the affected limb or area, cleaning the wound site if present (with debridement of dead tissue if necessary) and treatment with oral antibiotics, except in severe cases, which may require admission and intravenous (IV) therapy. Flucloxacillin monotherapy (to cover staphylococcal infection) is often sufficient in mild cellulitis, but in more moderate cases or where streptococcal infection is suspected then usually combined with oral phenoxymethylpenicillin or intravenous benzylpenicillin, or ampicillin/amoxicillin (e.g. co-amoxiclav in the UK). Pain relief is also often prescribed, but excessive pain should always be considered relevant, as it is a symptom of necrotising fasciitis, which requires emergency surgical attention.

Prevention

Any wound should be cleaned and dressed appropriately. Changing bandages daily or when they become wet or dirty will reduce the risk of contracting cellulitis. Medical advice should be sought for any wounds which are deep, dirty or if there is concern about retained foreign bodies.

Cellulitis in horses

Horses may acquire cellulitis, usually secondary to a wound (which can be extremely small and superficial) or to a deep-tissue infection, such as an abscess or infected bone, tendon sheath, or joint. Cellulitis from a superficial wound will usually create less lameness (grade 1-2 out of 5) than that caused by septic arthritis (grade 4-5 lameness). The horse will exhibit inflammatory edema, producing a hot, painful swelling. this swelling differs from stocking up in that the horse will not display symmetrical swelling in 2 or four legs, but only in one leg.

This swelling begins near the source of infection, but will eventually continue down the leg. In some cases, the swelling will also travel upward. Treatment includes cleaning the wound and caring for it properly, the administration of NSAIDs, such as phenylbutazone, cold hosing, applying a sweat wrap or a poultice, and mild exercise. Veterinarians may also prescribe antibiotics. Recovery is usually quick and the prognosis is very good if the cellulitis is secondary to skin infection.

References

• Cellulitis Overview (with picture).
• King, Christine, BVSc, MACVSc, and Mansmann, Richard, VDM, PhD. "Equine Lameness." Equine Research, Inc. 1997. Pages 548-549.
• MFMER. 'Cellulitis'. 3 July 2002. Mayo Foundation for Medical Education and Research. 30 Oct. 2003 [1].
• NLM. 'Group A streptococcal infections'. 2002. National Library of Medicine. 30 Oct. 2003 [2].
• Pankey, George A. "Approach to rashes and infections of the skin and subcutaneous tissues." Textbook of internal medicine. 2nd ed. 2 vols. Philadelphia: J. B. Lippincott Company, 1992.