Cellulitis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Cellulitis is a skin infection that causes inflammation of the connective tissue underlying the skin. Cellulitis can be caused by the infection of normal skin flora or by exogenous bacteria, and often occurs in places where the skin has previously been broken: cracks in the skin, cuts, blisters, burns, insect bites, surgical wounds, or sites of intravenous catheter insertion. Cellulitis mainly affects the top layer of skin, but it may also affect the tissues underlying the skin. Skin on the face or lower legs is most commonly affected, although cellulitis can occur on any part of the body. This inflammation can disseminate throughout the body if it spreads to the lymph nodes and bloodstream. When the deeper layers of the skin are involved, the condition is known as fascitis. If it involves the musculature, it is known as myositis. A particularly serious condition is orbital cellulitis, in which bacteria infect the eye or tissues around it.

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

Microorganisms gain initial access into the layers of the skin through the discontinuities and cuts in the skin. The body responds to these microbes as foreign bodies and their detection sets off an inflammatory response. The inflammatory response leads to redness, swelling, pain and itching of the area involved.^[1]

The most common causative microbes of cellulitis are Streptococci and Staphylococcus aureus. Another causative microbe is the bacteria Pasturella multocida.^[1]

• Staphylococcus ^[1]

Cellulitis should be distinguished from thrombophlebitis, contact dermatitis, insect stings, drug reactions, and arthritis.^[2]

The elderly, patients with impaired circulation to and drainage from the extremities, and those with weakened immune systems are especially vulnerable to contracting cellulitis.^{[3][4] [5]}

Cellulitis can be complicated by the development of sepsis, osteomyelitis, lymphangitis, endocarditis, meningitis, and gangrene. The prognosis of cellulitis is good provided the patient starts on an antibiotic treatment regimen.

Cellulitis is most often a clinical diagnosis, and local cultures do not always identify the causative organism. Blood cultures are usually positive only if the patient develops generalized sepsis. Conditions that may resemble cellulitis include deep vein thrombosis, and stasis dermatitis.

Cellulitis is mainly a clinical diagnosis based upon a patient’s history, symptoms, and physical examination. Physical exam indications such as warmness of the affected area, erythema, and swelling of nearby nodes can confirm the diagnosis.

With changing trends in medicine, recommended lab investigations are changing. Blood cultures and blood counts are the mainstay for the treatment and prognosis of cellulitis. Other blood tests such as ESR and CRP assist in prognosis. Levels of ESR and CRP taken at a patient’s admission may predict the severity and duration of hospitalization.

Imaging may be considered when bone involvement in suspected and if a foreign body in-situ is one of the differentials.

In cases of deep abscess or occult abscess, and in cases of orbital cellulitis, a CT scan can be quite useful in differentiating pre or post septal.

Soft tissue involvement is seen in cases of untreated or in rapidly spreading progressing cellulitis. MRI can be of great value in such cases.

Ultrasound can be used in cases of occult abscesses. It useful in aspiration of pus in children and reduces hospital stay.

Typically a combination of intravenous and oral antibiotics are administered for the treatment of cellulitis. Empiric broad spectrum antibiotics are started and subsequently modified according to culture reports. Bed rest and elevation of the affected limbs are recommended to accompany the antibiotic treatment. In patients with edema of the extremities, compressive stockings may aid in treating the fluid accumulation. Small abscesses surrounding the affected tissue can be treated with a simple incision and drainage of the fluid. It is advised to drink plenty of fluids during your treatment and recovery.

Good hygiene and good wound care lower the risk of cellulitis. Any wounds 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 any concern about retained foreign bodies. Diabetics should be advised routine self foot inspection.

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• There is limited information about the historical perspective of cellulitis.

• There is limited information about the historical perspective of cellulitis.

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Cellulitis can be classified according to the Dundee classification.

In 2011, Marwick et al modified the previously used Eron classification to stratify patients according to severity^[1]. The criteria for severity were based on systemic signs of sepsis along with taking into account their Standardized Early Warning Score (SEWS) and patient comorbidities. The SEWS is a form of an early warning system, where the physician calculates a score using the patient’s clinical observations, with the score of 4 indicating the most severe presentation^[2]. The SEWS was found to be lacking and patients were either undertreated or overtreated^[3]. New tools are being developed to accurately stratify patients according to risk^[4].

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aditya Govindavarjhulla, M.B.B.S.

Cellulitis results from the activation of the body’s inflammatory response to bacterial exposure. In the absence of an appropriate immune response to the initial bacterial invasion, the infection can spread systemically through the bloodstream. Certain risk factors predispose an individual to develop cellulitis which includes the breaking of the skin, previous unresolved skin infections, and immunosuppression.

Through breaks and discontinuities in the skin barrier, microorganisms have a portal of entry into the layers of the skin. The body responds to these microbes as foreign bodies and their detection initiates an inflammatory response. This response leads to redness, swelling, pain, and itching of the area involved. A local infection leads to inflammation of the area involved. With a competent immune system, the spread of the infection is limited. If the immune system fails to curb the initial infection, the infection may become systemic by spreading into adjacent areas. If the infection spreads to the bloodstream, it is called Bacteremia.

Group A streptococcus and staphylococcus ^[1] are the most common causative agents of cellulitis. These bacteria are part of the normal flora of the skin but they will cause infection if the skin is broken. Predisposing conditions for cellulitis include insect bites, animal bites, pruritic skin rash, recent surgery, athlete’s foot, dry skin, eczema, burns and boils. Another cause may be Hemophilus influenza, especially in cases of facial infections.Closing </ref> missing for <ref> tag

In rare cases, the infection causing cellulitis can spread to the deep layer of tissue called the fascial lining. Necrotizing fasciitis, also called “flesh-eating disease” by the media, is an example of a deep-layer infection. It represents an extreme medical emergency requiring surgical consultation.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Group A streptococcus and [[staphylococcus]are the most common causative agents of cellulitis. These bacteria are part of the normal flora living on the skin.

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

• Group A streptococcus ^[1]
• Staphylococcus ^[1]

Less common causes of cellulitis include:

• Gram-negative aerobic bacilli ^[2]

The causative pathogen of cellulitis varies with the anatomical location and the patient’s medical and exposure history.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Aditya Govindavarjhulla, M.B.B.S.

Cellulitis should be distinguished from thrombophlebitis, contact dermatitis, insect stings, drug reactions, and arthritis.

Cellulitis must be differentiated from other causes of lower limb edema like chronic venous insufficiency, acute deep venous thrombosis, lipedema, myxedema, lymphatic filariasis and causes of generalized edema.

Cellulitis can be promptly diagnosed with an appropriate history and physical exam. Administration of an antibiotic therapy will initiate resolution of the condition in 2-3 days. Differentials have to be thought of only when resolution is not seen. Non- resolution of cellulitis can be due to infection by resistant strains of the bacterium involved.

There are many dermatological conditions which manifest in manner similar to cellulitis. Careful evaluation of each case, based on accurate history and physical examinations, is very important. Differentials are as follows:

• Erysipelas is a skin infection caused by Streptococcus pyogenes, similar to cellulitis, but it affects superficial layers of the skin. It has more demarcated edges than cellulitis.

• Erysipeloid is a skin infection which is mostly occupational in nature. It is most commonly seen in people involved in the poultry and meat industry. It is characterized by local lesions, diffuse lesions and systemic forms.

• Deep vein thrombosis is a condition in which a blood clot is formed in the deep veins. It can be differentiated from cellulitis by the presence of tenderness along the clotted vein. Duplex ultrasonography would reveal the clot in the vein.

• Necrotizing fasciitis looks like cellulitis at the onset of the disease but it is much more serious. Large amounts of pain, necrosis, and bullae are noticeable. It often requires surgical exploration.

There are a few conditions which can be misdiagnosed as cellulitis such as thrombophlebitis, contact dermatitis, insect stings, drug reactions, arthritis.^[9]

• Contact dermatitis is an inflammation of the skin in response to direct exposure to an allergic or irritating substance. This inflammation is usually present with papular erythematous indistinct margins. The extent of distribution is often limited to the area of exposure.

• Insect bites cause a local reaction leading to the development of erythema, tenderness, pruritus and edema. In severe reactions, it can involve adjacent joints. In very severe cases, insect bites can lead to anaphylaxis.

• Drug rashes are the cutaneous presentation of a drug reaction. The rashes are variable, ranging from a pinkish hue to an exanthem. The rash can be limited or widespread. Itching is the most common symptom. If fever, dehydration and involvement of membranous surfaces is present along with the rash, then other diagnoses have to be considered. Drug rashes present most commonly when taking drugs such as sulfa, anticonvulsant drugs, and insulin from animal sources.

• Arthritis presents as pain in the joints, but at times it can be severe enough to present as erythema. At times, septic arthritis can infect overlying skin and can cause cellulitis.

• Some autoimmune conditions may mimic symptoms of or actually cause cellulitis. Panniculitis, Familial Mediterranean Fever, and Hyper IgD syndrome can present erythema and other systemic symptoms.

• In leukemic patients, some times cancerous cells infiltrate the skin causing erythema, papules, and nodules. The cause of these symptoms has to be differentiated by immunostaining.

Cellulitis must be differentiated from other diseases that cause bone pain, edema, and erythema.

Cellulitis is most commonly seen in the middle-aged and older adult population with a higher incidence among males. Higher rates of disease have been observed in warmer months with an incidence of about 200 cases per 100,000 patient-years. ^{[1] [2] [3]}

• The incidenceof cellulitis is approximately 200 case per 100,000 individuals worldwide.

• Cellulitis commonly affects middle-aged and older adults.^[4]

• There is no racial predilection to cellulitis.

• Cellulitis affects men and women equally.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1], Associate Editor(s)-In-Chief: Aditya Govindavarjhulla, M.B.B.S.

The elderly, patients with impaired circulation to and drainage from the extremities, and those with weakened immune systems are especially vulnerable to contracting cellulitis.

Common risk factors for the development of the disease include:

The elderly and those with weakened immune systems are especially vulnerable to contracting cellulitis. ^[1]

Diabetics are more susceptible to cellulitis than the general population because of their impaired immune systems. Diabetics are especially prone to cellulitis in the feet because diabetes causes impaired blood circulation in the legs. This impaired circulation in the legs leads to the development of foot ulcers that commonly become infected. Cellulitis is also a common complication of obesity. ^{[2] [3]}

Immunosuppressive drugs, HIV, and other illnesses or infections that weaken the immune system are also factors that make infection more likely. In addition, chickenpox and shingles often result in broken blisters which can provide an entrance to the skin through which bacteria can enter.

People who previously have had cellulitis are at risk of another flare up. Patients with a previous history of bacteremia were also found to be at significantly higher risk of recurrent bacteremia. ^[4]

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

Skin disorders such as eczema and athlete’s foot can result in breaks in the skin that serves as routes for bacterial infection.

Other risk factors for the development of disease include:

Lymphedema, which causes swelling of the arms and legs, can also put an individual at risk for cellulitis. ^[5]

Cellulitis is extremely prevalent amongst dense populations sharing hygiene facilities and common living quarters.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aditya Govindavarjhulla, M.B.B.S.

Cellulitis can be complicated by the development of sepsis, osteomyelitis, lymphangitis, endocarditis, meningitis, and gangrene. The prognosis of cellulitis is good provided the patient starts on an antibiotic treatment regimen.

Cuts and wounds on the skin are the most common means of contracting cellulitis. Other conditions may also lead to the condition. Staphylococcus aureus and Group A Streptococci are the most common causative agents of infection. When the bacteria invades the skin, they release toxins which cause local erythema, pain, and induration. With a course of oral antibiotic treatment, cellulitis can be cured.^[1] Cellulitis spreads fairly fast, and if the disease is not treated it can lead to multiple serious complications.

Cellulitis can be complicated by the development of:

• Blood infection (sepsis)
• Bone infection (osteomyelitis)
• Inflammation of the lymph vessels (lymphangitis)
• Inflammation of the heart (endocarditis)
• Meningitis
• Shock
• Tissue death (gangrene)

Cellulitis usually subsides within 7-10 days of antibiotic use.^[2] Longer treatment may be needed if the cellulitis is more severe. This may occur if the patient has a chronic disease or their immune system is not working properly. People with fungal infections of the feet may have cellulitis that keeps recurring. The cracks in the skin from the fungal infection allow bacterial entry into the skin.

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