What Rheumatologists Really Need for Ultrasound Is…

After I graduated from a Rheumatology fellowship, I was invited to stay on as junior faculty and several years thereafter the ACR (that acronym stands for American College of Rheumatology – I have no idea why most people who are into ultrasound always think it means something else…) developed an educational initiative aimed at bringing MSK US to every Rheumatology training program in the USA.

The ACR began to invite about 20 training programs per year to nominate one faculty member whose journey through the Ultrasound School of North American Rheumatologists (USSONAR) would be subsidized by the College. The idea was that each USSONAR graduate would then start an MSK US training program at his or her home institution, and since there are only about 120 Rheumatology training programs in the USA, the whole process would only take about 6 years. The rate of adoption among training programs was of course not 100%, and there are several key barriers to the development of an ultrasound training program, but at our institution it worked.

I’ve been doing point-of-care MSK ultrasound ever since I completed USSONAR and passed my certification exams, and our institution now has a required half-day MSK ultrasound clinic in which every Rheumatology fellow spends 6 months as part of their required curriculum. While MSK US certification is not required for graduation or to sit for boards, I’m proud to say that so far three of our Rheumatology graduates have opted to sit for the exam and are now ultrasound certified.

The program has been in place for about 7 years now, so it seems a good time to begin reflecting on my impressions of how MSK US fits into a Rheumatology practice, and more importantly some of the ways in which the current off-the-shelf technology doesn’t fully meet our specialty’s needs.

Clearly, MSK US is a major boon to Rheumatology in terms of needle guidance. Our half-day ultrasound clinic has made it possible for us to stop referring hip injections out to Interventional Radiology or Anesthesia-Pain, and I’m hoping that we will soon be able to bring sacroiliac joint injections back in-house as well. Diagnostically, the most common reason a patient is referred to the ultrasound clinic is for disambiguation of the borderline / nebulous case—that patient who endorses symptoms that sound like active inflammation but whose physical exam is benign. Our most common diagnostic referral is to answer the question of whether or not subclinical synovitis is present in the small joints of the hands, and that leads us to the first instance of current MSK US technology being less than a seamless integration into clinical practice and more of a square peg being jammed into a round hole.

The soft tissues associated with the small joints of the hands are at very shallow depths, usually under 1 cm in most patients. My very first ultrasound machine was a SonoSite M-MSK, and you adjusted the depth with a pair of pushbuttons. The standard procedure (and I would teach the fellows exactly this) was to start up the machine and then just start tapping the “less depth” button over and over.

Image of a finger joint with a ruler indicating the small height of the joint  is less than 2 centimeters.

“Just keep tapping,” I would tell the fellow. “Tap it like you’re playing Space Invaders, and just keep hitting it until the machine starts beeping in protest because the minimum depth has been reached.”

Even at that minimum setting, most ultrasound machines still show a depth of about 2 cm. I often joke with the fellows that this setting would be wonderful if we were trying to look clear through the patient’s hand and figure out what material the cushion on the exam table was made of!

Astute readers will also realize that no matter what the depth on the machine is set to, this puts the target structure (again, usually at a depth of 0.5–1 cm) closer to the probe face than the optimal focal zone distance on many probes—we are giving ourselves a case of technological hyperopia.

A stand-off pad will help keep the tissue at a better focal distance, but these pads can be cumbersome and will make the learning curve for any fellow even steeper than it already is by virtue of obscuring the tactile input, which is integral to the hands-on nature of point-of-care sonography. Ultrasound doesn’t feel like a natural extension of the physical exam with a stand-off pad in the way.

The real solution here is to switch to ultra-high-frequency ultrasound, something in the 50–70 MHz range, where the depth bar at the edge of the monitor is labeled in millimeters instead of centimeters. For small joints, I think this has to be the future of MSK ultrasound. This is why I was interested in the AIUM’s Community on High Frequency Clinical and Preclinical Imaging, and ultimately volunteered to serve among its leadership. Sadly, these UHF machines are expensive and they are often purpose-built for ultra-high-frequency only, meaning that a top of the line Rheumatologic MSK US clinic would need to own two machines, one UHF and one standard.  

This won’t fly in most places.

One of the main reasons why the ACR’s vision for an MSK US curriculum in every Rheumatology training program has not been fully realized is the expense involved in acquiring even one machine.

When we are looking at the hands of that patient whose clinical presentation is ambiguous—whose symptoms don’t seem to match their physical exam and in whom occult synovitis is suspected—we are looking for three telltale sonographic signs of the ravages of inflammation: hypertrophy of the synovium, the presence of a joint effusion, and hyperemia from the irritated joint lining struggling to summon blood flow to meet its elevated metabolic demands. The first two are often lumped together under the umbrella of “grayscale findings,” and the hyperemia is of course measured by Doppler.

The second hurdle for MSK US in the field of Rheumatology, then, is that of Doppler sensitivity. We are trying to examine and even semi-quantify the blood flow in capillaries, using equipment designed to measure the jets from regurgitant heart valves. Power Doppler is helpful here, due to its independence from the angle of insonation, but again we end up playing every trick in the book (starting with turning the wall filter off completely, if the machine even allows it) trying to squeeze every iota of signal out of the noise.

I always start the hand exam with a calibration image, in which I capture the blood flow in the pulp of a fingertip. Sometimes, especially in the midst of Chicago winters, you can’t even tell the Doppler is on at all. Currently, there’s nothing to do in that situation other than to comment in the report that Doppler calibration failed and thus the sensitivity of the study for detecting active synovitis (the very thing for which the study was ordered) is significantly compromised.

Taken together, it would seem that perhaps what we really need is for manufacturers to go beyond a blanket “MSK” setting in their machines and offer a true “Rheum” optimization package.

Dr. Mandelin is an academic rheumatologist, registered in MSK ultrasound (RhMSUS) by the American College of Rheumatology and certified in MSK ultrasound (RMSK) by the Alliance for Physician Certification & Advancement. He currently serves the AIUM as secretary of the High Frequency Clinical and Preclinical Imaging Community.

Where do you think MSK ultrasound is headed? Rheumatologists, where else does the technology not quite work in terms of your practice? Comment below or join in the conversation on Twitter, where my handle is @NU_Rheum_MSK_US.

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