Abscess

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Overview
An abscess is a collection of pus that has accumulated in a cavity formed by the tissue on the basis of an infectious process (usually caused by bacteria or parasites) or other foreign materials (e.g. splinters or bullet wounds). It is a defensive reaction of the tissue to prevent the spread of infectious materials to other parts of the body.

The organisms or foreign materials kill the local cells, resulting in the release of toxins. The toxins trigger an inflammatory response, which draws large numbers of white blood cells to the area and increases the regional blood flow.

The final structure of the abscess is an abscess wall, or capsule, that is formed by the adjacent healthy cells in an attempt to keep  the pus from infecting neighboring structures. However, such encapsulation tends to prevent immune cells from attacking bacteria in the pus, or from reaching the causative organism or foreign object.

Abscesses must be differentiated from empyemas, which are accumulations of pus in a preexisting rather than a newly formed anatomical cavity.

Manifestations
The cardinal symptoms and signs of any kind of inflammatory process are redness, heat, swelling, pain and loss of function. Abscesses may occur in any kind of solid tissue but most frequently on skin surface (where they may be superficial pustules (boils) or deep skin abscesses), in the lungs, brain, teeth, kidneys and tonsils. Major complications are spreading of the abscess material to adjacent or remote tissues and extensive regional tissue death (gangrene). Abscesses in most parts of the body rarely heal themselves, so prompt medical attention is indicated at the first suspicion of an abscess.

Treatment
Wound abscesses do not generally need to be treated with antibiotics, but they will require surgical intervention, debridement and curretage.

Incision and drainage
The abscess should be inspected to identify if foreign objects are a cause, requiring surgical removal. If foreign objects are not the cause, a doctor will incise and drain the abscess and prescribe painkillers and possibly antibiotics.

Surgical drainage of the abscess (e.g. lancing) is usually indicated once the abscess has developed from a harder serous inflammation to a softer pus stage. This is expressed in the Latin medical aphorism Ubi pus, ibi evacua.

In critical areas where surgery presents a high risk, surgery may be delayed or used as a last resort. The drainage of a lung abscess may be performed by positioning the patient in a way that enables the contents to be discharged via the respiratory tract. Warm compresses and elevation of the limb may be beneficial for skin abscess.

Primary closure
Primary closure has been successful when combined with curettage and antibiotics or with curettage alone. However, another randomized controlled trial found primary closure led to 35% failing to heal primarily and primary closure longer median number of days to closure (8.9 versus 7.8).

In anorectal abscesses, primary closure healed faster, but 25% of abscesses healed by secondary healing and recurrence was higher.

Antibiotics
As Staphylococcus aureus bacteria is a common cause, an anti-staphylococcus antibiotic such as flucloxacillin or dicloxacillin is used. With the emergence of community-acquired methicillin-resistant staphylococcus aureus MRSA, these traditional antibiotics may be ineffective; alternative antibiotics effective against community-acquired MRSA often include clindamycin, trimethoprim-sulfamethoxazole, and doxycycline. (However, if cellulitis rather than abscess, consideration should be given to possibility of strep species as cause that are still sensitive to traditional anti-staphylococcus agents such as dicloxacillin or cephalexin.) It is important to note that antibiotic therapy alone without surgical drainage of the abscess is seldom effective due to antibiotics often being unable to get into the abscess and their ineffectiveness at low pH levels.

Recurrent infections
Recurrent abscesses are often caused by community-acquired MRSA. While resistant to most beta lactam antibiotics commonly used for skin infections, it remains sensitive to alternative antibiotics, ie clindamycin (Cleocin), trimethoprim-sulfamethoxazole (Bactrim), and doxycycline (unlike hospital-acquired MRSA that may only be sensitive to vancomycin IV).

To prevent recurrent infections due to Staphylococcus, consider the following measures:
 * Topical mupirocin applied to the nares . In this randomized controlled trial, patients used nasal mupirocin twice daily 5 days a month for 1 year.
 * Chlorhexidine baths, In a randomized controlled trial, nasal recolonization with S. aureus occurred at 12 weeks in 24% of nursing home residents receiving mupirocin ointment alone (6/25) and in 15% of residents receiving mupirocin ointment plus chlorhexidine baths daily for the first three days of mupirocin treatment (4/27). Although these results did not reach statistical significance, the baths are an easy treatment.

Magnesium Sulphate Paste
Historically abscesses as well as boils and many other collections of pus have been treated via application of magnesium sulfate paste. This works by drawing the infected pus to the surface of the skin before rupturing and leaking out, after this the body will usually repair the old infected cavity. Magnesium sulphate is therefore best applied at night with a sterile dressing covering it, the rupture itself is not painful but the drawing up may be uncomfortable. Magnesium sulphate paste is considered a "home remedy" and is not necessarily an effective or accepted medical treatment.

Perianal abscess
Perianal abscesses can be seen in patients with for example inflammatory bowel disease (such as Crohn's disease) or diabetes. Often the abscess will start as an internal wound caused by ulceration or hard stool. This wound typically becomes infected as a result of the normal presence of feces in the rectal area, and then develops into an abscess. This often presents itself as a lump of tissue near the anus which grows larger and more painful with the passage of time.

Like other abscesses, perianal abscesses may require prompt medical treatment, such as an incision and debridement or lancing.