Cellulitis overview

# Overview
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.

# Pathophysiology
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.

# Causes
The most common causative microbes of cellulitis are Streptococci and Staphylococcus aureus.  Another causative microbe is the bacteria Pasturella multocida.
- Staphylococcus 

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

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

# Natural History, Complications and Prognosis
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.

# Diagnosis

## History and Symptoms
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.

## Physical Examination
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.

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

### CT
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.

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

# Treatment

## Medical Therapy
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.

## Primary Prevention
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.