Today, we're gonna talk about bacterial
skin and soft tissue infections.
As we do, let's start with a case.
This is a 37-year old man with a history of opioid use disorder
and injection drug use who presents with fever and arm pain.
He reports that he uses about 15 bags of heroine a day and often
"sterilizes" his needles by licking them before injecting.
3 days ago, he noted pain,
redness and swelling in his right forearm.
Overnight, he noted progression of the redness and he developed
fevers and chills leading him to present to the hospital.
He has no other past medical history.
He takes no medications,
no recent travel and no history of blood clots.
He does smoke about 10 cigarettes
a day but does not drink alcohol.
Family history is non-contributory.
And review of systems reveals no
dyspnea, no joint pain, and no nausea.
Moving on to the physical exam,
he is febrile to 38.5 degrees celsius.
Heart rate's 92, blood pressure's okay.
Head, neck exam: normal sclerae,
Cardiopulmonary exam is benign,
importantly, there's no murmurs.
His abdomen is soft, nontender and nondistended.
Examining his extremities, we see multiple
track marks in the antecubital fossa bilaterally.
There's an ill-defined 6x4 cm patch of erythema,
warmth induration, mild tenderness in the right foream
distal to the antecubital fossa with central
puncture wound and equivocal central fluctuants
There's a small amount of purulent fluid
expressed when applying pressure to that area.
There is on exam, an epitrochlear lymph node.
There's no proximal erythema or crepitus
He has no pain with elbow range of motion,
and there's no axillary lymphadenopathy.
In addition, you don't detect any palpable cords.
Shown here on the right, is a representative picture
of this patient absent the aforementioned track marks.
Okay, with that case presentation,
what's our most likely diagnosis?
Let's start with the top.
So erysipelas is usually caused by Strep. pyogenes.
And patients with this diagnosis tend to present more acutely
and may progress very rapidly over the span of 12-24 hours.
Our patient's story was really over 2-3 day period.
Importantly, erysipelas si non-purulent.
It only involves the upper layers of the
dermis and the superficial lymphatics
Our patient seems to have some evidence of purulence
by pushing on the area and some pus was coming out.
In addition, more often than not,
erysipelas is on the face, oftentimes in children.
And there's a clear demarcation between the involved
and uninvolved areas with a raised, advancing border.
There's not a subtle, blurred distinction between
the infected lesion and the non-infected skin.
So I think we can safely take erysipelas off of our list.
Next up is cellulitis.
And when you're thinking about cellulitis,
you should also be aware of certain risk factors.
The first of which is any break in the skin.
Our patient is using injection drugs so
he's frequently having breaks in the skin.
Another common one would be tinea pedis,
which you'll often see in diabetes.
Diabetes in its own right, even without tinea
pedis is a risk factor for getting cellulitis,
as is venous stasis due to the
interruption of lymphatic flow
and HIV because it's an immunocompromised state.
Our patient has some suspicion of a collection
or an abscess deep to the superficial findings,
which is something that we would definitely see with cellulitis
particularly if it's caused by community acquired MRSA.
Next up, speaking of severe
infections, is necrotizing fasciitis
Now patients with nec fasc, which is the
most severe skin and soft tissue infection,
will oftentimes have tenderness and pain
out of proportion to the exam initially.
Unfortunately, eventually as the disease
progresses and you have progressive necrosis,
they may actually have a diminished sensation to pain.
You're looking at edema beyond the borders of the erythema.
You may have crepitus due to the gas
gangrene and bullae may form as well.
Now for necrotizing fasciitis,
patients will almost always have some risk factor,
with diabetes, HIV or perhaps being
immunocompromised by immunosuppresant medications.
We're not getting that story from him so
I think we can safely x that one out too.
Septic thrombophlebitis needs to be
considered and needs to be excluded
in anyone with injection drug use who has
fevers, swelling and redness.
So I have to keep that one on our list for now.
And lastly, impetigo.
Let's talk about that one in a little bit more detail.
So impetigo is a bacterial infection most
often caused by staph and strep organisms,
and there's a good picture of it shown here.
Just like in this example, it's typically occuring
in patients who are ages 2 to 5 years old,
or in the elderly and certainly
in those who are immunocompromised
It starts off with just papules but then can
progress into vesicles with surrounding erythema
and ultimately these pustules with honey-crusted
adherent fluid when they open up and they rupture.
They're most likely to be on the face,
around the lips and the mouth or on the proximal limbs.
At times, especially if staph aureus is
involved, the lesions maybe bullous
and then they can ulcerate causing
something called an ecthyma.
These lesions are not itchy.
They may rapidly progress however to a deeper
infection with significant complications
like lymphangitis, furunculosis,
cellulitis which we've talked about before.
and even staphylococcal scalded skin syndrome
which is caused by an exfoliative toxin.
Post-streptococcal glomerulonephritis may be a late
manifestation, days to weeks after the initial infection.
For mild forms, like the one we're seeing here,
you can probably get by with just topical mupirocin
but for moderate or severe cases, you're gonna want to
use oral antibiotic directed against staph and strep.
And a good example of that would be
oral cephalexin or dicloxacillin.
So let's look again at the key aspects of this case.
So this is a 37-year old guy with opioid
use disorder and injection drug use.
That's gonna predispose him to any number
of different skin and soft tissue infections
but I'm most thinking about cellulitis.
The time course being about 3
days, also goes with cellulitis
rather than erysipelas which is
much more of a quick presentation.
Pain, redness, swelling - pretty typical for cellulitis.
Fevers and chills when we see that,
we worry about deeper infections and potentially bacteremia
And he does not have a history of blood clots which at least
is gonna steer us away a little bit from thrombophlebitis,
so I do think we're gonna need
some imaging just to be sure.
Looking at our physical exam, again for
some key features:
He is febrile, he does have an
ill-defined 6x4 cm patch
Again, if we were thinking about erysipelas,
there'd be a very well-demarcated border,
with a little bit of bullous changes.
There's mild tenderness in the right forearm which at
least tells us he doesn't have late necrotizing fasciitis.
He has equivocal central fluctuant which is most
likely associated with some deep tissue abscess.
An epitrochlear lymph node is comonly seen in patients who have
any skin and soft tissue infection if you go looking for it.
And importantly, there's no palpable
cords to suggest thrombophlebitis.
Here's some initial data to help us through.
So unsurprisingly, a white count of 13.1
BMP is fine -that's reasurring.
Liver function tests are okay.
Blood culture is reasonable to get if a fever is present but keep in
mind that it's useful in less than 10% of cases of cellulitis.
Wound culture can be helpful if the lesion is purulent
And I agree in this case, it's reasonable to consider an
ultrasound in light of his history of injection drug use.
In this case, our ultrasound says no "evidence of
thrombosis" we can take that off of our list
Soft tissue edema is present, that's no surprise
And we find a 1x1 cm fluid collection
deep to the central skin lesion.
Whenever you have a fluid collection
in the setting of cellulitis,
it's probably more likely to be
community acquired MRSA as the cause.
Incidentally, a d-dimer would not
be particulary useful in this case
With the setting of an infection, it's most likely to be positive
which could lead you down a path you don't want to go down.
So it looks like we can officially call this bacterial
purulent cellulitis likely from either staph or strep.