Ultrasound of Arthritis: Gout, Psoriatic, Degenerative, Seronegative - HD

Introduction

Hello, my name is John Jacobson.
I'm a musculoskeletal radiologist at the University of Michigan.
My talk, which I'll be lecturing on, is ultrasound of arthritis, gout, psoriatic, degenerative and seronegative.
Disclosures include, I'm a consultant for BioClinica and I receive book royalties from Elsevier, or the images in this lecture are copyrighted by Elsevier.

Approach to Arthritis

My approach to arthritis by any imaging method includes trying to decide if the arthritis is degenerative or inflammatory.
This is a key distinction in an algorithm of deciding what type of arthritis is present.
The hallmark of a degenerative process is the presence of osteophytes with minimal, if any, synovial proliferation.
In contrast, inflammatory arthritis is characterized by synovial proliferation with possible erosions.
Some types of inflammatory arthritis include what's called enthesitis, which is inflammation of an enthesis.
The enthesis is the bone attachment of a ligament or a tendon.
What is critical is to correlate the imaging findings of ultrasound with radiographs and also with laboratory values.
Radiographs are important not only to look at the appearance of bone changes, to differentiate osteophytes from erosions, but also to look at the distribution of the ultrasound findings, which helps us to determine the differential diagnosis.

Introductory Comments on Synovitis

A few introductory comments first about synovium.
When we're looking for synovitis with ultrasound or MR for that matter, we are screening synovial locations, which include joint recesses, bursae, and tendon sheaths.
Typically synovitis is hypoechoic compared to the adjacent subcutaneous fat.
Although some synovitis cases may be more isoechoic or even hyperechoic to the subcutaneous tissues.
Hyperemia is a very important asset to evaluate with ultrasound.
This will represent the activity of the inflammation and color or power Doppler imaging.
Remember that if an arthritis patient is being treated even with just non-steroidal anti-inflammatory drugs, that this can cause a decrease in the amount of hyperemia.

Rheumatoid Arthritis Examples

Here's the case of rheumatoid arthritis, looking in the sagittal plane of the dorsum of the wrist, here's the characteristic appearance of synovitis where we see hypoechoic of the radiocarpal and midcarpal joints with internal flow indicating inflammation or synovitis.
Here are two companion cases of rheumatoid arthritis with different echogenicity of synovitis.
Here in the hip joint, we can see that the synovitis is nearly isoechoic to the subcutaneous fat.
Where here is a more characteristic hypoechoic appearance.
Many people are moving away from the term synovitis in that this case here could actually represent a chronic burned out synovial proliferation rather than a true synovitis.
Usually the more acutely hyperemic active synovitis is an example here where more burned out treated synovial proliferation tends to be more hyperechoic.
Here are two companion cases of rheumatoid arthritis without and with flow on color Doppler imaging.
Again, patients who are being effectively treated can see a decrease in the flow and this can be one of the earliest signs that treatment is indeed effective.

Distinguishing Synovitis from Complex Fluid

Now when you're looking for synovitis in a joint recess or a bursa, many times it's difficult to distinguish between complex fluid and synovitis because both can produce distension of a space with complex echoes.
To make this distinction, if something is compressible with no internal flow or if the debris redistributes or moves, that implies complex fluid in contrast to a joint recess where it's distended, but non-compressible with internal hyperemia, which is more likely true synovitis.
On your left is a case of rheumatoid arthritis of the ankle.
What this shows this distension of the anterior ankle joint recess, much of the tissue here is hypoechoic approaching even isoechoic to the subcutaneous fat.
But note the more echoic area here with compression with the transducer, we see collapse of this area indicating that this is the fluid component and this is the synovial component.
And this person had synovial proliferation from rheumatoid arthritis and septic joint.
The needle was directed to this area to provide that diagnosis.
And your right is another example, but this is one where there is joint fluid.
The pitfall here is that if a joint recess is so markedly distended, it may not compress.
So be aware that a non-compressible joint could still contain fluid if significantly distended.

Bone Findings in Arthritis

Another introductory point has to do with looking at bone.
Remember the hallmark of arthritis differentiating degenerative from inflammatory is looking at synovitis in the soft tissues and also looking at the bone differentiating osteophytes from erosion.
It turns out that ultrasound is not very good when looking at erosions, although better than radiographs.
This study looking at the hand and wrist showed only 40% sensitivity and 29% false positive predictive value.
So ultrasound can show a lot of bone irregularity but is often very non-specific and a very time consuming process.
And that is why when looking for inflammatory arthritis, we emphasize the synovial search and de-emphasize the bone findings because of the poor sensitivity and false positive rate.
However, if you do see bone irregularity and there's adjacent synovitis, then you could say that the bone irregularity is truly due to an erosion.
So the synovitis adds specificity to the bone erosion.
And also keep in mind the importance again of looking at radiographs lab values and the distribution of findings.

Examples of Cortical Irregularity

Here are four different cases with four different diagnoses showing cortical irregularity.
The first is of the finger showing the collateral ligament with an erosion enthesitis edema and inflammation of the collateral ligament characteristic of psoriatic arthritis.
The next case at the thumb is osteoarthritis.
This is not an erosion, although it looks like one.
These are actually abnormal osteophytes.
The problem here is that this is the valley is in the problem, it's the peaks.
Here are the osteophytes.
The next case is one of rheumatoid arthritis where we indeed see bone erosions.
We see hypoechoic synovitis at the ulnar styloid.
Then lastly, the normal variant, the pseudo erosion at the second metacarpal head as shown here.
This looks like an erosion, but it's the characteristic site of this normal variant and there is no adjacent synovium.
These pseudo erosions not only occur in the second metacarpal head, but occur in other metacarpals as well as the metatarsals to a lesser extent.

Gout

So let's talk about three areas in this lecture now that we've covered the fundamental or introductory comments.
First, let's talk about gout.
So gout is crystal deposition of monosodium urate crystals.
These crystals can be deposited inside the joint where it can be in the synovium or the hyaline cartilage producing a joint process.
They also can be deposited around the joint or periarticular in the capsule tendon ligament or bursa where it can form a tophus.
And if it adjacent to the bone can produce an erosion uncommonly, a tophus can be deposited directly into bone.

Intraarticular Gout

So let's look at the intraarticular variety of gout.
So these crystals within the joint can cause a joint effusion.
Although nonspecific, we often see tiny little white dots within the fluid called microtophi.
Also these little calcifications, these crystals floating in the joint can cover the hyaline cartilage called cartilage icing, which produces the double contour sign.
More in that in just a moment, intraarticular involvement of gout can also produce non-specific synovitis adjacent erosions.
And we know that the great toe is the most common site for gout, but I wanna emphasize the knee.
Is it also a very common site that we should not forget?
Here are two cases of a gout of the ankle joint non-specific findings.
Here we see hypoechoic anechoic fluid, the normal hyaline cartilage interface, and here we see more hypoechoic synovitis.
Both of these could be from infection, it could be from rheumatoid arthritis, but these turned out to be gout.
Here's another example.
At the first MTP joint where we see distension of the joint recess, what we see here is that this was non-compressible with internal flow.
So rather than being complex fluid, this is synovium, although non-specific, we're starting to see tiny little white dots, which would emphasize maybe this is due to gout.
Also note the first MTP joint the most common site of gout.
So putting these two signs together, findings together, this would let us to believe that this non-specific synovitis could be from gout.

Double Contour Sign

So I mentioned the double contour sign.
This is where the tiny calcifications or the crystals that are in the joint are deposited and laying on top of the hyaline cartilage.
And what's been shown is that this finding disappears when the serum is less than six mg per dl.
Here, taking from the literature Dr. Wakefield's article showing the normal hyaline cartilage in the trochlea of the knee.
Here we see tiny white dot laying on top of the hyaline cartilage, which is the double contour sign in contrast to calcification within the cartilage term chondrocalcinosis in CPPD or pseudogout.
So these little crystals laying on top of the hyaline cartilage is what we're looking for to indicate gout.
Here are two companion cases.
Here are the MTP joint and the ankle joint showing these crystals laying on top of the hypoechoic hyaline cartilage.
Now it's important to distinguish this from the normal cartilage interface sign.
As you know if the sound beam hits the cartilage at 90 degrees, you'll see a thin white line at the interface of the cartilage.
We make the distinction between the double contour sign and the cartilage interface sign in two manners.
First of all, when we're looking at the interface down the slope of the bone or obliquely, you should not see the cartilage interface sign that only occurs at 90 degrees.
That is in contrast to the double contour sign where these little white crystals here, it's still reflecting the sound beam.
So we see this in spite of this being down the slope of the curve.
The second way to make this distinction from the cartilage interface sign is that this is not a smooth white line, but we see dots or irregular areas.
So that's another sign that this is the double contour sign.

Periarticular Gout and Tophi

As I mentioned, you can also have these crystals deposited not in the joint but also around the joint.
Often the form of a tophus, these can produce erosions that have overhanging edges seen on radiographs.
They can be deposited within tendons and ligaments as well and even into bursa.
So let's look at these different appearances of gouty tophi.
So ultrasound is a very specific feature of these tophi where it appears as a wet clump of sugar with a hypoechoic halo or rim.
MR is very sensitive for tophi as it is for many abnormalities in the musculoskeletal system, but is very non-specific.
So here's an example of a tophus by ultrasound.
We see this cloud-like area, it looks like a cumulus nimbus cloud, although hyperechoic.
There are still other brighter dots within it, which are the tophi and microtophi within the larger tophus.
Note the halo around this involving the tibialis anterior tendon.
Here's a case with MR correlation.
The MR shows edema and enhancement completely nonspecific.
If there's a soft tissue ulcer, this would be infection, this could be a tumor if it were some other bone.
But if we look at the ultrasound of the same case, we now see the classic appearance of the tophus cloud-like and emanating from the joint and the erosion.
So the appearance of an ultrasound is classic.
The location of the first MTP joint, putting that together is now pathognomonic.
So the foot is the most common site for gout.
As I mentioned, the first MTP joint, classically it's the medial and dorsal aspect of the distal first metatarsal where we tend to see erosions in a tophus.
You can see other sites involved as well, the other MTP joints and also the midfoot.
So keep that in mind as when looking for tophi and it can involve various tendons about the ankle and foot as well.
So here's another example involving the first MTP joint as they start the cine clip, you can appreciate the synovium, which is somewhat hyperechoic and these white dots of the microtophi.
With this large tophus sitting in this crater representing the erosion at the medial aspect of the distal first metatarsal head.
Here's a case if we look at the MRI first, it looks like tendinosis or maybe injury to the tibialis posterior tendon.
It's really non-specific.
There's no clue that this could represent gout other than perhaps noting the full extent of this abnormality.
It's really quite extensive, which would be uncommon for tendinosis or a tear.
You can look at the ultrasound.
We now see the classic appearance of the tophus with this cloudy appearance and these echoes.
So the ultrasound really adds specificity to the MR imaging findings.

Gout in the Knee

So other than the foot, the knee would be the second most common site of involvement with gout.
In fact, up to 30% of patients who are asymptomatic with hyperuricemia actually have tophi about the knee, not just fluid or synovitis, but they actually have tophi.
So it's important to keep this in mind when looking for gout.
Even if asymptomatic about the knee tophi tend to occur in two locations about the knee, the patellar tendon and the popliteus tendon.
They can even present as a mass clinically and appear like severe tendinosis.
They may also be deposited in the bursa in other spaces.
So here's an example of the double contour sign of the knee.
When bending the knee, we can see the trochlear cartilage and we see these white dots coming down the slope of the hyaline cartilage.
If we look at the medial compartment of the knee, we also see the double contour sign coating the hyaline cartilage of the femoral condyle.
Note that this is deposited and floating around between the interface of the medial meniscus and the hyaline cartilage.
This is not chondrocalcinosis, which would be within the meniscus or within the hyaline cartilage.
So again, these crystals are coating the surfaces of the cartilage of the hyaline cartilage and the fibrocartilage meniscus.
Here's a case of gout of the patellar tendon.
This could be perhaps mistaken for a mass or for diffuse tendinosis, but in fact an ultrasound.
We see this cloud-like area with partial shadowing, some increased density that's representing gout of the patellar tendon.
Here's a companion case looking at the popliteus, again, this is a very common site for gout.
It looks like severe tendinosis, but the question is why would you have tendinosis to this degree only involving the popliteus tendon with normal overlying fibular collateral ligament.
So if we look on ultrasound, we can see how this adds specificity to the MR diagnosis.
What we see here is this cloud-like area with an erosion in the popliteus as a groove.
So we might think about gout by the MR based on the extent of the abnormality and location, but ultrasound adds specificity note here in the radiograph, the slight increased density that we often see here in the setting of a tophus in the popliteus tendon.
Here's a tophus within the anserine bursa.
These tiny white dots represent microtophi that's filling this inflamed bursa.
Here's a more chronic case where we see some mineralization and calcification of the tophi, the pes anserine bursa, we see microtophi, larger tophi, some degree of shadowing.
Pes anserine bursa is a very common site for gout.
Here's a more non-specific case where we see hyperemia inflammation, bone erosion.
A differential here would include rheumatoid arthritis and infection and worried about the latter.
You would want to guide a needle into this and aspirate or perform a synovial biopsy.
Here's an example of gout involving the extensor tendon of the wrist.
And this is a peritendinitis with inflammation and these bright dots could represent tophi, but this is a more non-specific appearance.
But this is another case of gout.

Seronegative Spondyloarthropathies

Alright, let's move on to the seronegative spondyloarthropathy cases.
This is less commonly imaged and less common than let's say rheumatoid arthritis.
So let's compare and contrast to rheumatoid arthritis, which of course is the more common systemic inflammatory arthritis.
So like RA or rheumatoid arthritis.
This also involves synovial joints.
So when looking for seronegative spondyloarthropathy, we will indeed look at the synovial spaces.
We'll look at the bursa, the joint recesses, tendon sheaths and look for erosions.
You may also have involvement of cartilaginous joints, which would be unlike rheumatoid arthritis, but this is a big difference compared to rheumatoid arthritis.
Unlike RA. Here you can have inflammation of the tendon or ligament attachments or the enthesis causing an enthesitis.
On a radiograph you'll see some fluffy enthesophytes and erosions and hyperemia and you can have more diffuse bone proliferation about the extremity.
These are findings you do not see with the rheumatoid arthritis.
Another difference is distribution.
We know that rheumatoid arthritis involves the proximal parts of the hands and wrists and the feet.
Where these seronegative spondyloarthropathy cases have a more variable pattern.
It can be asymmetric, it can be just a single digit and other very variations of that.
So there are three seronegative spondyloarthropathies including psoriatic arthritis, reactive arthritis, and ankylosing spondylitis.
And the key to the differential is the distribution psoriatic arthritis.
When we look with ultrasound, we can see in the hand and the foot with reactive arthritis, usually younger males we tend to see in the lower extremity.
Ankylosing spondylitis is primarily the central skeleton.
So much less commonly do we see anything about the hands and the feet.

Psoriatic Arthritis Examples

So here's a case of psoriatic arthritis.
Now this is a non-specific case.
What we see is synovitis bone erosion, tenosynovitis around the extensor carpi ulnaris.
This could very well simply be rheumatoid arthritis.
So it is non-specific, but putting together the clinical picture, the distribution and radiographic findings, this was consistent with psoriatic arthritis.
There is a patient looking at the finger.
Now I normally don't scan the finger in every patient for arthritis, but as I mentioned, people with these seronegative spondyloarthropathies will tend to have a swollen digit and guide you to a location to search.
And what we see here is a thickened collateral ligament.
We have an erosion, some fuzzy periarticular studies and inflammation.
So the patient pointed at this area and we see the classic features of psoriatic arthritis.
Now here's another case showing the importance of radiography.
Here when I'm looking at the ultrasound, we see tremendous bone irregularity.
At first thought you may think, well these could be erosions, but the clue that these are not erosions is the extent of the bone marrow abnormality.
Because erosions typically occur where the joint is in touching the bone, meaning that there's contact with synovium.
If you have such diffuse involvement, even places that aren't touching a joint, that's a clue that there may be another cause for the bone irregularity.
And indeed, on the radiograph we see tremendous bone proliferation throughout every area of the carpus.
So these aren't erosions, this is simply bone proliferation.
Another hallmark of psoriatic arthritis.
Here we see an example of a seronegative arthritis of the elbow showing non-specific synovitis.
This could be infection, this could be RA, but I'm showing a companion case where we see complex fluid, which is septic joint that can look very similar.
We would hope that we'd see swirling here or this may redistribute with joint movement.
Unlike this, which would be non-compressible with or without hyperemia to suggest true synovitis.

Enthesitis

And here's a case of enthesitis.
At the distal triceps we see hypoechoic thickening, bone irregularity and hyperemia.
So you might ask, how can I differentiate this from tendinosis?
Well, first of all, hyperemia is less common in the site, but one of the keys is the bone irregularity.
If the bone irregularity is well-defined, that would imply degenerative process and need be tendinosis.
If the bone is fuzzy or irregular, that would imply in ankylosing spondylitis or a seronegative spondyloarthropathy.
Often that's difficult to determine on an ultrasound and that's why relying on radiograph can be very helpful.
The radiograph should show fuzzy periosseous and enthesitis where if it were degenerative it would be well-defined.

Osteoarthritis

And then finally we're gonna end this talk by talking about osteoarthritis.
Now we typically don't perform ultrasound for osteoarthritis because it's a classic clinical presentation and also the radiographs are usually diagnostic.
The term osteoarthritis refers to a degenerative joint disease, specifically involving a synovial articulation.
There may be some mild inflammation, but it's typically secondary to the cartilage wear that tends to be mechanical.
This usually occurs at specific joints after the age of 40 and specific times in our life.
So one of the first joints to wear out is the acromioclavicular joint.
And then after that, the thumb base and the great toe, usually over the age of 40 to 50.
Then the DIP joints, depending on how much we use our hands and then later on the knees in the hip after our bodies start to wear out after the age of 40.
So what we're looking for by ultrasound are osteophytes, although these are better seen on radiographs, but also joint effusion, which is completely non-specific.
You may see synovial proliferation minimal, if any.
You may see hyperemia, although not too frequently and you may see in particular loose bodies, also possibly shown on radiographs if calcified or ossified.

Osteoarthritis Examples

So here's a case of the thumb base showing osteophytes about the thumb base.
This is not an erosion, but again, these are osteophytes creating a pseudo erosion.
There is some mild hyperemia and synovitis here.
Now you might ask, why wouldn't this be rheumatoid arthritis?
Well, if this were the second metacarpal head in the correct clinical setting, this would be consistent with it.
But because this is a thumb base where we see osteoarthritis all the time and rarely see RA and putting together with the clinical findings and the radiographs, this is consistent and compatible with osteoarthritis.
Remember that when you have osteoarthritis at the thumb base specifically was called the trapeziometacarpal joint, the scaphotrapezium trapezoid compartment.
There's a high association with flexor carpi radialis tendinosis and tearing.
Here's an example of knee osteoarthritis of looking at the medial compartment where we have an extrusion of the meniscus.
We have hypoechoic area here with degeneration.
We have MCL edema and bone joint space narrowing and osteophytes.
Again, many of these findings are best seen on radiography, especially weight bearing radiography.

Summary

So just to summarize first, a few take home points.
The first being synovium, we reviewed where we look for synovitis, meaning synovial spaces, joint recesses, tendon sheaths and bursa.
It's typically hypoechoic and we need to assess for hyperemia.
To me, this is the great advantage of ultrasound and looking for inflammatory arthritis is looking for synovitis.
We can't see it on radiographs and we can see fairly well with ultrasound.
Erosions are a secondary sign of inflammatory arthritis, but there are a lot of difficulties here.
We're not sensitive or specific enough.
It takes a long time to actually look for these.
So basically this I deemphasize erosions and emphasize the synovium.
If I do see bone irregularity, I'm not gonna ignore it.
I'll rely on the synovitis and other findings on radiographs lab values to add specificity to the erosions,
We talked about enthesitis.
This in the setting of the seronegative spondyloarthropathies at ligament tendon attachments or looking for hypoechoic thickening of the structure with erosions and hyperemia because these can be anywhere in the body, usually the patient or the radiograph guides us to the specific part of the body to look for enthesitis.
And then I showed an example of bone proliferation.
Remember with the seronegative spondyloarthropathy that you could have bone proliferation anywhere around the bone, not just at the joint surfaces.
We did spend a lot of time on gout because ultrasound has some very characteristic features.
We mentioned the double contour sign, the classic appearance of the cloudy with a hypoechoic rim of a tophus.
And then more nonspecific findings.
And we highlighted the characteristic locations and distribution, the great toe, the medial aspect of the metatarsal, and also about the knee.
And we highlighted the tophi in the popliteus and the patellar tendons.

Search Patterns for Diagnosis

So three final slides.
The first, when I have a patient with inflammatory arthritis of the wrist and hand, how do I go into the room and efficiently and effectively make a diagnosis?
Well, in my mind, I'm trying to put the diagnosis into one of three categories based on history, clinical findings, laboratory findings, and radiographic findings.
I'm thinking either rheumatoid psoriatic or osteoarthritis.
If rheumatoid, I go to my synovial search pattern looking at the dorsal compartments of the radioulnar radiocarpal, midcarpal joints and the MCP PIP joints and looking at tendon sheaths.
If I see synovitis, I'll look deeper and try to look for erosions.
If I'm thinking psoriatic arthritis, I'm gonna start with a synovial search, but also include an enthesitis search based on the radiographic or clinical findings to guide me to specific tendon, a ligament attachments that wouldn't have been otherwise on my search pattern.
If I'm thinking osteoarthritis, which is usually the thumb base or the distal interphalangeal joints, we mainly rely on the radiographs.
But here we're looking for osteophytes, maybe some mild synovitis.
And keep in mind adjacent tendon problems.
When looking at the ankle foot, I'm also thinking rheumatoid psoriatic or reactive arthritis or osteoarthritis.
I'm adding gout into my search pattern.
So if I'm thinking RA, similar to the hand and wrist, I'm looking at the synovial spaces.
But I do wanna highlight one thing.
The fifth metatarsal head is a very common site for RA in the foot.
In fact, it's uncommon to have RA at the other joints without fifth.
The fifth MTP joint involvement for the psoriatic or reactive arthritis.
Again, synovial search pattern, adding the enthesis wherever the findings may be seen clinically or at radiographs.
For gout, we highlighted the first metatarsal head medially and also the osteoarthritis likes the first metatarsal.
So what's interesting about the ankle in the foot is that the first metatarsal is a very common target site for three of the four different entities of inflammatory arthritis and osteoarthritis.
And then finally, I want to emphasize one final time is that we really need to correlate with the history, the lab values, the radiographs, and look at the distribution to add specificity to often non-specific findings of inflammatory arthritis as seen by ultrasound.
Thank you very much for your attention.