Hey this is Dr. K from imedicalschool and today lets talk about cellulitis. We will

rev iew the causes of cellulitis, the differential diagnoses , as well as, the management of

cellulitis.

First we need to understand what exactly is cellulitis. Cellulitis is an infection that

involves the skin and soft tissues. The parts of the skin that are involved include the

Dermis,a s well as, the subcutaneous tissues. In addition to an infection of the tissue

an abscess amy be present. An abscess is a walled off collection of pus that are generally

resistant to antibiotics unless they are incised and drained. Now what organisms are commonly

responsible for cellulitis. Well remember that your skin is the first line of defense

for your body from outside pathogens. When you have breaks in your skin from cuts or

trauma bacteria are able to enter into the deeper layers of tissue. As a result the most

common organisms involved in cellulitis are really the organisms that are constantly present

on your skin. These organisms include beta hemolytic strep and staphylococcus aureus.

More recently methiccilin resistant staphylococcal aureus, otherwise known as MRSA has become

significantly more prevalent within the community and should especially be considered when an

abscess is present.

Now besides cellulitis are there other skin infections that can appear similar to cellulitis.

Well the first one we will talk about is erysipelas. Erysipelas is an superficial cellullitis that

has a defined raised border, which is key. Erysipelas is cause by the bacteria beta-hemolytic

strep. The reason it is important to differentiate erysipelas from cellulitis is that the antibiotics

used are slightly different because in erysipelas we are really trying to tagret beta-hemolytic

streptococcus. In add-on to erysipelas we should always be mindful of necrotizing infection.

Necrotizing infection lead to significant cell death. Many organisms can be responsible

but what is so scary about necortizing infections is that they can threaten the limb and if

severe enough can lead to limb amputation so it is always best to catch necrotizing

infections early when all they may need is some localized debridement.

Now what are the risk factors that may predispose individuals to cellulitis. If we know what

risk factors predispose people to cellulitis we will be better able to identify and possible

prevent cellulitis in these groups of patients. First off obesity is a known risk factor for

cellulitlits as it has many associated problems like increased venous congestion and gthe

development of a greater number of skin folds where bacteria can grow if not properly cleaned.

The presence of edema or prior radiation therapy increases your risk of cellulitis. Hospitalizations

increase your risk of celluliitis and can increase your risk of developing MRSA cellulitis.

If walk down the hospital hallway it is clear to see how many rooms are on contact isolation

because someone has an MRSA infection or their skin is colonized with MRSA. Of course intravenous

drug abuse predisposes people to cellulitis as they are breaking the skin barrier with

many times dirty needles and introducing bacteria into the deeper tissues. Finally the last

two risk factor include being diabetic and immunocompromised because both of these groups

are unable to mount an appropriate immune response. Diabetics are prone to cellulitis

because they can develop neuropathy or chronic numbness from their diabetes and they may

not be able to feel that minor cuts they receive are becoming infected. This is the reason

that all diabetics should do daily foot care to identify of any scrapes ro cuts are infected

on their feet. THis is one of the major reasons why many uncontrolled diabetics undergo leg

amputations which is really sad to see.

Now what are the keys to the physical exam? Well it is really important to identify the

areas affected by cellulitis. You really should take a marker and outline the edge of the

area affected. Drawing a border will help you and other health care providers to see

if the cellulitis is improving or worsening on their antibiotic therapy. In addition because

necrotizing infections are so severe it is important to try to identify necrotising fascists

early. On physical exam when you press on the affected area if you feel or here a crackling

or popping sensation this may represent subcutaneous gas produced by a bacteria in a necrotizing

infection. if this were present he patient would need urgent surgical evaluation. Most

of the time though subcutaneous gas will be better appreciated on X-ray or MRI. of the

affected area. In addition make sure to identify if the skin infection is plain old cellulitis

versus erysipelas with the demarcated raised borders. Other consideration would be to consider

if the patient has osteomyelitis. Osteomyelitis i an infection of the bone. As infection penetrate

the skin the can progress to deeper tissues, so they can affect muscles, tendons, and if

they get deep enough even bone. Usually a significant wound is present if a patient

is at risk for osteomyelitis. If a patient has osteomyelitis do not swab the skiing to

identify the bacteria involved because all the bugs on the skin flora will grow out but

rather have a bone culture performed to identify what is causing the osteomyelitis.

In terms of workup I would always start with a CBC with a differential to help identify

if a leukocytosis is present. In addition obtain an ESR and CRP. ESR is the erythrocyte

sedimentation rate and CRP is c-reactive protein. Bothe these labs are indicators of inflammation

within the body but are not specific to any particular cause for the inflammation. ESR

and CRP will not tell you what type of infection is occurring but may indicate to you the severity

of the infection based on how high these lab values are. In addition you could follow these

labs through treatment to see if there is a decrease in inflammation with antibiotic

treatment to figure out if your treatment is working. Generally I do not follow ESR

and CRP but in rare cases where for some reason it is difficult to tell if the cellulitis

is improving I may consider repeating the CRP and ESR several days after admission.

Given that we want to assess the severity of the skin infection it is important to obtain

blood cultures as the blood cultures will identify a bactaremia that means whether the

bacteria that is infecting the skin has been able to start growing in the blood, which

would indicate a severe infection and changes the course and rout of antibiotics that you

need. If a patient is bactaremic they must be treated with IV antibiotics and not oral

antibiotic.s. Also consider if imaging needs to be performed. Imaging studies can help

you identify necrotizing infections as well as osteomyelitis. IF you are suspecting osteomyelitis

make sure to obtain above culture.

In someone with cellulitis it is important to keep in mind a broad differential because

you do not want to miss any of the mimics of cellulitis and get the diagnosis wrong.

As i have mentioned previously make sure a patient does not have necrotizing fascitiis.

in addition a infection that can mimic cellullitis is called herpetic whitlow. Herpetic whitlow

is an infection by herpes zoster, the bug that causes chicken pox, of a inter. You will

see small vesicles with underlying red skin. Keep in mind this is a viral infection and

not a bacterial infection so antibiotics will not help this. A patient with herpetic whitlow

will likely need antiviral therapy. In addition make sure your patient does not have a hypersensitivity

reaction which means an allergy. Allergic responses can mimic a cellulitis picture.

Finally make sure the patient does not have a clot or DVT in the legs or arms. A blood

clot can present with swelling and redness of their underlying skin. A detailed history

and physical should point your clinical suspicion towards or away from cellulitis.

Now lets talk about the treatment of cellulitis. Cellulitis can be treated on an outpatient

basis if not severe. The key finding that dictates treatment is whether the cellulitis

is purulent, producing pus, or not. if the area affected is purulent there is a concern

for MRSA so think about using clindaymycin or TMP.Sx; if they are penicillin allergic

you could consider doxycycline. Linezolid is another outpatient agent that can be sussed

that would also cover MRSA. If the cellulitis is non purulent then consider cephalexin,

dicloxacillin, or clindamycin. THese antibiotics are mainly pointed at streptococcus.

Finally lets talk about inpatient treatment. In the Inpatient setting for patients that

are very sick I would consider starting with vancomycin as it will cover all your gram

positive organisms, as well as, MRSA. Now if someone has a chronic diabetic wound I

would consider adding antipseudomonal coverage so you could consider an antibiotic like piperacillin

tazobactam, otherwise known as Zosyn. always remember the key rule is to tailor antibiotics

based on the culture data to decrease the risk of bacteria developing resistance and

your patient from developing complications. Eventually you should be able to wean to oral

medications after significant improvement. Well that is a brief review of cellullitis.

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THis is Dr. K and I will see you next time.