Okay we're gonna jump now
into the topic of septic arthritis.
Here's the case:
A 48-year old marketing consultant presents
with fevers and right knee pain and swelling
for the past 2 days.
Denies any recent trauma or obvious triggers.
No recent travels, no recent sexual activity
nor any recent gastrointestinal infections.
He does report that he binge drinks and
occasionally uses cocaine intravenously
on the weekends when hanging
out with his childhood friends.
He's gone hiking several
times in the past few weeks.
A lot of different historical
information there that may guide us
when we're starting to
generate a differential diagnosis.
He smokes about 10 cigarettes per day,
he's divorced and not currently sexually active.
Family history, he has an uncle
with inflammatory bowel disease.
We'll see if that's
relevant or not.
And review of systems: no nausea, no vomiting,
no diarrhea, no abdominal pain or hematochezia.
He does report however some malaise, and some fatigue.
So whenever reading a history and
physical presented to you on a board question,
it's gonna be really important to figure out why the authors
of the questions are including or excluding certain features
And in this case, there's a lot of excess
information here for us to go through.
First, let's pick out the four
most important variables.
So it looks like this is a fairly acute presentation,
it's only been there for about the past 2 days.
Pattern of joint involvement.
We're dealing with a
It's just the right knee and that's gonna help us
when we're thinking about our differential diagnosis.
Thirdly, is there joint inflammation?
This is a hot, swollen, tender knee - that's the
textbook definition of what an inflamed joint looks like.
So yes, we have joint inflammation.
And fourthly, is there evidence
of systemic involvement?
Not a hundred percent clear
but the patient is reporting fevers.
We have some malaise, some fatigue, so it looks like there
probably is some sort of systemic process going on here.
Highlight in bold are several
other useful pieces of information
and on the next slide we'll talk about
why those particular pieces are relevant.
So again, absence of GI infections, the presence
of intravenous cocaine use, the binge drinking,
recent hiking, lack of sexual activity, and
family history of inflammatory bowel disease
and again, those review
of systems pieces as well.
So let's head into our differential diagnosis.
Non-gonococcal septic arthritis, Lyme disease,
Gout, gonoccocal septic arthritis and reactive arthritis.
Now the bad news is that all five of these could
be characterized by acute monoarticular arthritis
with fevers and
Some are certainly more inclined to
have oligoarticular or polyarticular symptoms
but they can all start
off with a single joint.
So we're gonna need some more
information and hopefully those details
that we put in bold on the last
slide will help guide us through.
So what are the features that will
distinguish amongst these diagnoses?
Okay, non-gonococcal septic arthritis.
The knee is the most common
joint involved and typically it's MRSA
or methicillin-resistant Staph.
aureus that's gonna be the pathogen.
Because that's the most common pathogen,
we think about what factors would lead somebody
to become bacteremic and end
up with bacteria in their joints.
So, injection drug use - he is using cocaine
intravenously, that's gonna be a risk factor.
Similarly, prior surgery, any procedure
that involves breaking the skin,
rheumatoid arthritis or gout.
Those things can all contribute to an
increased risk of a non-gonococcal septic arthritis.
So we have to leave that
one on our list for sure.
Turns out the knee is also the most
common afflicted joint in Lyme disease.
So we've got to leave
this one there as well.
His recent walk in the woods could
certainly have exposed him to ticks.
What's missing though is the absence of a headache
and he doesn't have any of that classic "bulls eye" rash
or erythema chronicum migrans that
we would look for with Lyme disease
but nonetheless, not every
patient presents with that.
So we'll have to keep
that on the list as well.
Well, the most common joint for gout is the 1st MTP
- that is the metatarsophalangeal joint of the big toe.
More common than the knee but
absolutely, people can get gout in the knee.
He is relatively young for gout.
We're not giving the information that he's
obese and they gave us a lot of other information,
but he does drink alcohol.
He does not have CKD and men are
more common than women to develop gout.
So we've got some things going for
and some thing's going against gout
We'll have to keep
that on the list.
Fourth, gonococcal septic arthritis.
This is usually characterized
by migratory polyarthralgias
so multiple joints being painful and not
necessarily having big, hot swollen joints.
More often do involve the small to medium-sized
joints - the finger joints, the wrists, the ankles,
and classically for gonococcal septic arthritis, or disseminated
gonoccocal infection is another term that we would use,
patients may have some pustules or vesicles
on their palms or on the soles of their feet.
We'd expect the patient of course since we're
talking about gonorrhea to have recent sexual activity,
more common amongst young
group, men and women for that reason,
and for whatever reason, it
is more common in women.
It doesn't seem like we have a lot
going for gonococcal septic arthritis.
The last piece we'll look for is tenosynovitis which is
inflammation of the synovial sheaths around tendons.
And again, we'll keep it on the list but it seems less
likely based on the information that we have thus far.
Next on our list, reactive arthritis.
So this is one of the axial spondyloarthritides and
it is characterized by lower extremity oligoarthritis.
So again, the knees, the ankles ,
not unlike what we have in our patient.
Such patients with the reactive arthritis have an
antecedent genitourinary or gastrointestinal infection.
Our history specifically said he did not
have any recent gastrointestinal infections.
The age is right though.
Typically, ages range from 20-40
and the other things we'll
be looking for are enthesitis.
That's basically inflammation of
the insertion of a tendon into a bone,
most commonly at the Achilles
tendon or perhaps at the elbow.
Eye symptoms - anterior
uveitis would be a concern.
Lower back pain,
urethritis, and dermatitis.
One of the classic things you might hear
when you're thinking about reactive arthritis is,
"can't see, can't pee,
can't climb a tree"
It rhymes - it's easy to remember.
And lastly, the typical HLA pattern for folks with reactive
arthritis as well as the other axial spondyloarthritides
would be an HLA-B27 haplotype
In our case, not a lot going for that but
we should really keep it in our list for now.
So let's look at the physical exam.
He is in fact febrile, temperature
is 37.9 degrees Celsius.
heart rate's 88, blood pressure's okay.
He is thin, fit-looking, again, that's gonna steer
us away from the gout question, no acute distress.
He has no scleral or conjunctival injections, so it's
good to see there's no eye involvement at this time.
And unsurprisingly, the right
knee is grossly swollen and hot.
There's no other joints involved.
No tenderness to palpation of the
Achilles tendon or the plantar fascia
And you know why they
specifically mentioned that.
It's again talking about reactive arthritis which is prone to
having enthesitis at insertion points of tendons into bone.
In the skin, perhaps presumably because
of his injection drug use with cocaine,
he has some track marks
in his left antecubital fossa.
There's no vesicles or papules
or erythema chronicum migrans.
no keratoderma blenorrhagicum
or circinate balanitis.
Now those last two very complicated Latin
terms are referring to some of the classic findings
that we might see with
reactive arthritis as well.
The lack of ECM steers
us away from gout.
And the absence of vesicles or papules is gonna
steer us away from disseminated gonoccocal infection
cause you'd see those
lesions on the hands.
Finally, we'd get an arthrocentesis,
and this is where the money is.
This will help us to really understand
what is happening.
We have yellow,
opaque synovial fluid.
The white cell count is 72,000 white blood cells
which is polymorphonuclear predominant, 82%
There's no crystals, the gram stain is
negative and the culture is pending.
So, let's interpret that
synovial fluid cell count.
This is a gradient from less than 2,000 to greater
than 80,000 white blood cells in the synovial fluid
and the higher up you go, the more
inflamed unsurprisingly the joint is.
So typical things like osteoarthritis with
a little bit of an acute synovitis and OA,
you really shouldn't have more than 2,000 white
blood cells, you might only have a few hundred.
As you move up to a rheumatologic
disease and an inflamed joint from
say lupus or rheumatoid arthritis, you
can have 2 to 20,000 white blood cells
Gout's gonna be considerably more, it's really
an abundant inflammatory response initially with
macrophages and monocytes but then there's
this recruitment of polymorphonuclear cells
so 20,000-80,000 cells
would be pretty typical.
And once you get above 80, you're
really thinking about septic arthritis.
Mind you, you don't need to have
80,000 cells to think septic arthritis.
Our patient has 72,000 so we should
absolutely be keeping this on our differential.
It's right in that ballpark between
gout and infectious arthritis.
One thing we can say is that with a count of 72,000 we
can safely take reactive arthritis and Lyme off of our list.
Okay so now, revisiting our differential diagnosis, we can
safely take Lyme disease and reactive arthritis off the list
based on the relatively elevated cell count.
And now let's look at the remaining three.
I mean, gout is possible but his relatively young
age, and most importantly the absence of any crystals
is gonna steer us away
from that diagnosis.
So I'm comfortable taking that one off.
Now we're left with non-gonoccocal
and gonococcal septic arthritis.
So, now how are we gonna distinguish
amongst these last two remaining diagnoses,
gonococcal septic arthritis?
Well, looking at the gonococcal one first, he
doesn't really have migratory polyarthralgias.
He's got mostly involvement of his knees,
he doesn't have the pustules or vesicles
and most importantly he completely
denies any recent sexual activity.
Things really aren't going for that diagnosis.
In contrast, for non-gonococcal,
he's using injection drugs.
He's got the track marks to prove it.
He's likely to have gotten Staph.
aureus into his bloodstream.
It's fairly elevated at this point and again
the knee is the most common joint involved.