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.