Is Enthesitis Unique to Psoriatic Arthritis?

Psound Bytes Transcript: Episode 194

Release date: May 9, 2023

“Welcome to this episode of Psound Bytes, a podcast series produced by the National Psoriasis Foundation, the nation’s leading organization for individuals living with psoriasis and psoriatic arthritis. In each episode someone who lives with psoriatic disease, a loved one or an expert will share insights with you on living well. If you like what you hear today, please subscribe to our podcast and join us every month at Psound Bytes for more insights on understanding, managing, and thriving with psoriasis and psoriatic arthritis.”

Shiva: My name is Shiva Mozaffarian and welcome to Psound Bytes! Joining me today for a discussion about the diagnosis of psoriatic arthritis, diagnostic biomarkers, and one of its hallmark symptoms enthesitis, is rheumatologist Dr. Lihi Eder. Dr. Eder is an Associate Professor of Medicine and the Canada Research Chair in Inflammatory Rheumatic Diseases Tier 2 at the Institute of Medical Science, University of Toronto. Dr. Eder’s research is focused on identification of novel methods including imaging modalities and laboratory biomarkers to improve early detection that hopefully allows appropriate intervention to stop the development of psoriatic arthritis. Dr. Eder is a past recipient of an NPF Discovery Grant for her work in the use of ultrasound and MRI to identify and characterize psoriatic arthritis. Welcome Dr. Eder and thank you for joining Psound Bytes™. Let’s first talk about the current diagnostic criteria for psoriatic arthritis such as CASPAR (or the Classification Criteria for Psoriatic Arthritis). How effective is the current criteria for diagnosing psoriatic arthritis?

Dr. Eder: So, the CASPAR criteria were developed to include people with psoriatic arthritis in clinical trials or in research. So they were not meant to be used for diagnostic purposes. But there's been several studies that looked into how sensitive these criteria are in identifying people with early psoriatic arthritis and they show that they are quite good. So they are quite sensitive, which is reassuring. So essentially anyone that has psoriasis that do not have rheumatoid arthritis and have typical features of psoriatic arthritis like arthritis or enthesitis or inflammation in the spine that is called sacroiliitis, they could meet the CASPAR criteria. So overall there is a very good performance of these criteria in the diagnosis. But I should mention though that there are some individuals that can have psoriatic arthritis, but they don't meet the CASPAR criteria. It doesn't mean that the fact that they don't meet CASPAR criteria, that they don't have psoriatic arthritis. So, this is really up to the rheumatologist that is managing their disease to make a decision whether they have this condition or not.

Shiva: So you mentioned enthesitis which is one of the domains of psoriatic arthritis. What are the remaining domains that factor into the diagnosis of psoriatic arthritis?

Dr. Eder: So the other domains or the basically, these are manifestations of the disease. They include the psoriasis, so the skin disease. They include psoriatic nail lesions which is the pitting or the onycholysis which is the separation of the nail from the nail bed. You mentioned the enthesitis, which is inflammation of the tendon insertion to the bone. Other features include arthritis, which is inflammation in the joint, dactylitis, which is swelling of the finger, or the toe like sausage, and the last manifestation is spondylitis or sacroiliitis, which is inflammation in the spine. So overall, these six manifestations of skin and musculoskeletal diseases comprise the disease of psoriatic arthritis, which makes it very heterogeneous, meaning every individual can have different combinations of these six domains which makes it more complex to manage and we as rheumatologist need to consider each and every one of these six domains when we manage this disease.

Shiva:And Dr. Eder what is the function of the synovial enthesis relationship? And how does this relationship factor into the dysregulation of the immune system?

Dr. Eder: So this is an excellent question and there's been some work that suggested that enthesitis or some people call it synovio-entheseal complex is the first site where inflammation starts in psoriatic arthritis. So, the enthesis which is based on the synovio-entheseal complex theory, it's not just that insertion point. It's actually functioning as an organ, so the enthesis is meant to move the joint or move the bone. For example, the Achilles tendon is an example of an enthesitis, and this area is subjected to a lot of biomechanical stress. Whenever we jump or run or do any exercise, the enthesis is handling all these stress on the bone and the joint. So in some individual that can lead to some micro injuries. Some injuries when they do a lot of these exercises and if they are predisposed psoriatic arthritis, caring some genes this could lead to having more chronic inflammation. So, these injuries can trigger inflammation that becomes more chronic, and it's been suggested that from the enthesis the inflammation can then spread into the joint. So, to the synovium which is close to that enthesis. So this is what differentiates psoriatic arthritis from rheumatoid arthritis, where the hypothesis is that the inflammation is starting inside the joint as opposed to psoriatic arthritis, where the inflammation would start at the enthesis which is outside of the joint. This is maybe one of the reasons that some of the biologic medications that work for psoriatic arthritis do not work for rheumatoid and vice versa some that work for rheumatoid don't work for psoriatic arthritis, and it is also explaining some of the differences that we see in the manifestations. We talked about the domains so enthesitis, for example, is not something that we find in rheumatoid arthritis. This is unique to psoriatic arthritis and to related conditions like spondyloarthritis, ankylosing spondylitis and so on.

Shiva: So, we know there are over 100 entheses in the body. What are the common locations where enthesitis occurs?

Dr. Eder: So yes, there are many, many entheses in the body, but not all of them are involved in psoriatic arthritis because enthesitis is really happening in unique type of enthesis that are fibrocartilaginous. So they are different type of entheses. Those that are associated or involved in psoriatic arthritis are those that I mentioned that are subjected to more biomechanical stress and has these fibrocartilage which is the component that helps to dissipate some of this stress. The most common locations are in the lower limbs around the knees and the ankles. I mentioned the Achilles tendon is a very common one. The plantar fascia is a common one and then the patellar tendon insertions around the knee are also very common. And then there are some other entheses in the upper extremities like in the lateral collateral ligament, which is sometimes called tennis elbow. This is causing pain in the lateral or in the side of the elbow. These are the more common locations of enthesitis and one of the reasons is probably that these areas are more subjected to this biomechanical stress that is causing some injuries to these entheses, which becomes more chronic in PsA and causing pain.

Shiva: Sounds like mechanical stress is key.

Dr. Eder: Absolutely.

Shiva: So how would someone know it's enthesitis versus tendonitis or fibromyalgia? You've mentioned some of it already but what are the characteristics of enthesitis?

Dr. Eder: Yeah, that's an excellent question and it's quite challenging because the physical examination of enthesitis is really based on the rheumatologist applying some pressure on these points which are, if this is in the side of the elbow or the Achilles tendon, and if the patient is experiencing pain, and then this may be a sign of enthesitis. But this is very subjective, right? Because people that experience fibromyalgia, they have pain in many many other sites and many of these sites are close to tender or sites that are commonly tender in healthy individuals. So just by recording these tender points this can be quite confusing to know whether this is fibromyalgia or this is enthesitis and this is where imaging like ultrasound can be quite useful because ultrasound can show whether the tendon is involved or not. There are specific findings like thickening, like increased blood flow at the enthesis which are very typical of enthesitis and are not typical or not found in fibromyalgia. So, using ultrasound in the clinic is a way to get an immediate answer whether this is fibromyalgia or this is enthesitis. And I use ultrasound in my clinic and especially for the diagnosis of enthesitis. Could help me make decisions regarding whether someone needs intensifying their treatment or they need to manage their pain and their approaches are very, very different.

Shiva: So what percentage of people with psoriatic arthritis develop enthesitis, and does having enthesitis mean someone will have a more severe form of psoriatic arthritis that may impact quality of life?

Dr. Eder: So up to a third of the people with psoriatic arthritis will have what we call clinical enthesitis. So, they would have pain in their entheses which is called clinical enthesitis. Whether this is also associated with some ultrasound findings this has not been tested. But overall, between a third or up to half of the patients in clinical trials would have enthesitis. So a lot of the people. If we do detect enthesitis by ultrasound, it has been associated with some outcomes like higher risk of developing joint damage. So it is a marker of more severe disease. So that's why it's important to treat it early and to manage it as we do manage arthritis. So it's not just inflammation in the tendon, it's a marker of severity. People with enthesitis can have quite debilitating disease with difficulties in walking or exercising or performing daily activities so certainly important to treat and control.

Shiva: And what medications are used to treat psoriatic arthritis and enthesitis?

Dr. Eder: So the enthesitis component in psoriatic arthritis, there are different treatments and really depends on whether it's the only manifestation, whether it's alone or whether it's associated with other things like inflammation in the joints. If enthesitis is associated with inflammation in multiple joints, then we typically manage it along with the other manifestations. Medications can be either by tablets, or injectables, and typically we usually start with things like methotrexate, leflunomide and then if they don't work or people cannot tolerate them, then we move on to more advanced therapies like the biologics. Especially with the biologics, there's been more data to support that they do work quite well for enthesitis. All of the clinical trials showed across all of the existing biologic medications that they are better than placebo and to treat enthesitis. We don't know yet whether one biologic is better than the other for the management of enthesitis. This is something that is really hard to compare across studies especially because enthesitis is not assessed as the primary outcome of the study. So, at this point any biologic should be reasonable option to treat enthesitis. The more difficult situation is when enthesitis is the only manifestation because we have very little data. If there is only one or two sites, then typically either treatment with non-steroidal anti-inflammatory drugs like naproxen or ibuprofen is usually given as a first kind of line and with a full dose for a few weeks. Injections of corticosteroids can also be given, and this is something that in some areas, some tendons, something that we as rheumatologist don't like to do as much because there is at least a theoretical risk of fracture of tendons such as the Achilles tendon. But, in some situations in some areas this is less of a concern. So, injections work quite rapidly especially if done under ultrasound guidance, they are probably less painful and more accurate in putting the steroids in the right place and work quite well. So these are sort of the two options. One is systemic therapies in combination especially if there are other manifestations or more localized temporary treatments NSAIDS or injections.

Shiva: Emerging diagnostic techniques which you have been at the forefront of and is the focus of your research is the use of imaging. Can you tell us more about how imaging is used to assess and diagnose enthesitis?

Dr. Eder: So, I mentioned that we want to diagnose people with psoriatic arthritis early. Enthesitis is quite difficult to pick up on physical exam and diagnose accurately, so this is where ultrasound is becoming a really important tool. We work now and I lead the group in GRAPPA who is developing a new diagnostic tool for psoriatic arthritis, specifically focusing on enthesitis and assessing enthesitis by ultrasound as a way to help us diagnose psoriatic arthritis early and start treating psoriatic arthritis early in order to prevent all of the long-term consequences of this condition. I do hope that we will have a new tool in the coming year.

Shiva: And what do you envision will be the future for use of such imaging?

Dr. Eder: So one really exciting advance in the field of ultrasound is the development of handheld ultrasound devices. The ultrasound, one of the limitations was that it's a big machine. You can't carry it from one room to the other. It can be quite expensive to purchase. So many rheumatologists were not adopting this technology because of the cost and because of the fact that they work in several clinics. You can't really carry it from one clinic to the other. And now, over the past several years, there has been huge advances in the technology of ultrasound and it became advanced in a way that it could be now put in a very small device that is the size of almost a cell phone which connects to an iPad. So this ultrasound can be carried into remote locations or outside of the clinic and also the cost of it is quite reasonable. So I think it brings a lot of opportunities to use ultrasound technology in the hands of people that were hesitant in adopting this technology in the past. People in the community that may not have the funds of people who work in a bigger academic centers and even trained allied health professionals such as a nurse practitioners in performing this and saving time for patients and helping with earlier diagnosis of psoriatic arthritis which we know that ultrasound could potentially help with.

Shiva: So how critical is it to diagnose and treat psoriatic arthritis in the early stages?

Dr. Eder: So, it is indeed very critical to diagnose and treat. So diagnosis is the first step because without an accurate diagnosis of psoriatic arthritis, we can’t treat appropriately. Not every person with psoriasis that has pain in their joints has psoriatic arthritis. They can have osteoarthritis, they can have fibromyalgia, they can have other things, and treating these other conditions with biologic treatment is not a good thing because these medications would have side effects and risks. So we need to diagnose early and diagnose accurately and without accurate diagnosis, we can’t treat people. There's been several studies that showed that diagnosing early and treating to target. So when we diagnose people and then see them on a regular and frequent visits and then when we treat to target, so we aim to reach remission or a minimal disease activity state. We evaluate very frequently and if they don't meet the targets then we switch or add treatment. Then it's been shown that this approach has a better long-term and short-term outcomes. So more people are able to reach remission and low disease activity states with this early diagnosis and treat to target approach. So overall I think both of them early diagnosis and frequent assessments by rheumatologists who are experienced in managing psoriatic arthritis are really critical for preventing long term complications such as development of joint damage and is associated with better outcomes of having the disease under control and with less influence on function and quality of life.

Shiva: Thank you Dr. Eder for such an interesting discussion about enthesitis and psoriatic arthritis. Do have any final comments you'd like to share with our listeners today?

Dr. Eder: Just thank you for having me and I'm happy to talk about psoriatic arthritis and my research to anyone who is willing to listen. I'm grateful to the National Psoriasis Foundation for supporting my research and thank you.

Shiva: Thank you again Dr. Eder for being here today. It's been such a pleasure exploring the function and relationship of enthesitis in psoriatic arthritis with you. May is Psoriatic Arthritis Action Month. For more information about the management of psoriatic arthritis and what you can do to help maintain your mobility contact our Patient Navigation Center by emailing or by calling (800) 723-9166, option 1 today. Finally thank you to our sponsors who provided support on behalf of this Psound Bytes™ episode through unrestricted educational grants from AbbVie, Bristol Myers Squibb, Janssen, and UCB.

We hope you enjoyed this episode of Psound Bytes for people with psoriasis and psoriatic arthritis. If you or someone you love has ever struggled with psoriatic disease, our hope is that through this series you’ll gain information to help you lead a healthier life and inspire you to look to the future. Please join us for another inspiring podcast. You can find this or all future episodes of Psound Bytes on Apple Podcasts, Spotify, iHeart Radio, Google Play, Gaana, and the National Psoriasis Foundation web page. To learn more about this topic or others please visit or contact us with your questions or comments by email at  

This transcript has been created by a computer and edited by an NPF Volunteer.

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