About cellulitis and erysipelas which act as areal skin infections. Cellulitis is a bacterial skin infection of the dermis and the subcutaneous tissue, the normal presentation of cellulitis is an infection in the lower limb such as near the tibia for example a good differential for cellulitis is another bacterial skin infection called erysipelas which is actually known as superficial cellulitis because it is an infection of the superficial dermal layer so let's just learn about erysipelas first. But first of all recap the anatomy of the skin.
The skin anatomy: The skin layers two main one's epidermis and the dermis below
the dermis if you are your subcutaneous tissue also known as the hypodermis which
is what actually makes up your superficial fascia below the superficial fascia
is a deep fascia a layer of connective tissue which surrounds organs such as
your muscle here. Erysipelas is an infection involving this area here which is
the superficial dermis again it is a superficial dermal infection, the main
causative agent is usually Group A streptococcus which is also known as strep
pyogenes, it is essentially a cocci a gram-positive coccus, the clinical
presentation of erysipelas classic one is an example of a patient coming in
with sort of a swelling inflamed butterfly appearing rash which is a good
differential for systemic lupus erythematosus besides from this the patient can
present with systemic features such as fevers, chills, Rygel's, as well as lymphatic involvement era syphilis, can also present in the lower limbs such as
in around the tibia for example and it has the Cardinal features of
inflammation which are very important.
These are warmth erythema which is redness tenderness as well as swelling so if we were to look at every sip list again in this skin diagram we could see that the whole skin area is markedly raised and it forms distinct borders and this is because you have inflammation of the superficial dermis which pushes everything up and in this area you also have your lymph vessels and it's valves coming all the way up to the superficial dermis and that is why you commonly get lymphatic involvement now that was erysipelas. Let's compare that to cellulitis the classic presentation of cellulitis as I mentioned is in the lower limbs such as around your tibia and this is classically in patients with risk factors such as diabetes. The other common presentation is in children around the eye this is called periorbital cellulitis and like erysipelas cellulitis has cardinal features of inflammation, you have warmth, you have erythema, you have tenderness and you have swelling.
So let's take a closer look at
cellulitis and see what happens in the skin itself cellulitis is a bacterial
infection involving the dermis more specifically the deep dermis and the
subcutaneous tissue and because it is a deeper infection a deep dermal infection
and subcutaneous tissue, the appearance of the skin is only a little bit of
swelling it's only slightly raised and you have more of indistinct water
clinically what you can do is in the area of infection you can use a marker and
draw around it and date it the next day you can see whether the infection is
getting worse and this is also an excellent way to see if antibiotic treatment is
working or not, the main causative agent of cellulitis is Staphylococcus
species such as staph aureus as well as beta-hemolytic streptococcus such as Group A streptococcus.
Let us now briefly look at the pathophysiology
of both erysipelas and cellulitis basically, you have bacteria who possess
verlan factors such as you to know you exfoliate of toxins and whatnot and these
verlan factors will allow the bacteria to penetrate and invade the skin
layers at the same time the patient has their own risk factors which will
increase their risk of developing cellulitis and so both the bacteria factors
and the patients risk factors will allow for inflammation to take place in the
dermis or the subcutaneous tissue area so what are these patient risk factors. Well, these risk factors include having a history of cellulitis tinea pedis are inter
digitalis which is basically a fungal infection in your toe webs allowing
basically axis of bacteria into the dermis area also if you have trauma
pre-existing skin conditions such as dermatitis also increases the risk other
risk factors include lymphedema, obesity, diabetes as well as venous insufficiency.
Cellulitis and erysipelas can be difficult
to distinguish however both are diagnosed clinically investigations that can be
performed include culture of wound foci so a focus within the wound can be
cultured however this is not often found an x-ray of the area of the limb can
also be done if you suspect complications such as osteomyelitis. Finally, you
can also culture the tinea into digitalis and you can also perform blood
cultures if you suspect sepsis and bacteremia also if you suspect the patient
has an abscess a contained infection or you can order an ultrasound. The
management of cellulitis and erysipelas is actually the same because the main causative
organisms of both are gram-positive bacteria such as staph aureus and Group A
streptococcus remember these guys gram-positive bacteria have an outer
thick peptidoglycan layer and then they have a plasma membrane below it and
then inside the cell they have proteins such as ribosomes.
Well, the management of erysipelas
and cellulitis are antibiotics first-line penicillins such as clocks
Esalen and flucloxacillin, the mechanism of action is that they inhibit cell
wall synthesis bacterial cell wall synthesis if the patient is hypersensitive
to penicillins so they have some form of reaction you can give cephalosporins
which are also beta-lactams and work the exact same way as penicillins they
inhibit cell wall synthesis of the bacteria however if the patient is
anaphylactic to penicillin so you probably don't want to use another beta-lactam and so no alternative is a drug such as clindamycin. Clindamycin works
by inhibiting protein synthesis and thus by disrupting protein synthesis you
essentially cause stasis of bacterial function complications of cellulitis and
erysipelas are a lot some common ones include sepsis as well as chronic edema.
Chronic edema occurs if you can
imagine if you have inflammation of the deeper skin layers you're essentially
increasing pressure and thus you don't allow the V. The veins return blood
to the heart and so its backflow is causing chronic edema.
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