VIDEO: Diagnostic challenges in psoriatic arthritis

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There are several diagnostic challenges in psoriatic arthritis. I would say that it ranges from identifying the presence of an inflammatory disease to differentiating that inflammatory disease from other inflammatory arthritis. So, you know, oftentimes the context in which somebody is coming in to see us is a patient with psoriasis who now has joint pain. And to my mind, oftentimes the first challenge is sorting out is this indeed an inflammatory arthritis, or is this something either mechanical or osteoarthritis or something else going on that's driving this pain? So for example, we know that in psoriasis, there's a higher rate of obesity. So we do see higher rates of things like osteoarthritis in this population, and it's not at all unusual for a patient to be sent over for evaluation for possible PSA and find that, in fact, there's no inflammatory arthritis to speak of. It's more of an osteoarthritic component. So there's that kind of initial diagnostic challenge.

On top of that and making things even more challenging is the presence of enthesitis and psoriatic arthritis. And I would say probably this is the bearer of diagnosing these patients, particularly because enthesitis can be challenging to pick up clinically and even on imaging. So we know that patients with psoriatic arthritis present with enthesitis, inflammation at tendon insertion sites, often that occurs in the heels, and it presents, for the most part, with pain in that region. And so if I have enthesitis at the elbow, obviously I'm going to have pain around the insertion side of the elbow. There's a few reasons this is a challenge, though. For one, a lot of these sites of enthesitis coincide with sites of common mechanical injuries.

So for example, the plantar fascia, the plantar fascia insertion in the heel is a very common cause of enthesitis, but unfortunately, it's also an exceedingly common cause of mechanical injuries, especially in runners. And so the patient with psoriasis who presents with heel pain on the plantar aspect of the foot, differentiating between is this vanilla plantar fasciitis, or is this enthesitis in the setting of psoriatic arthritis can be extremely challenging. That's all the more challenging when you see other sites, such as lateral epicondyle or medial epicondyle insertion, or in particular, if you're getting into enthesis along the back, if you're getting into kind of axial sites of enthesitis, this gets to be more and more challenging. These can be mistaken not only for kind of mechanical injury, but even for fibromyalgia tender points in patients that have polyenthesitis phenotype. Often these can look a lot like a fibromyalgia patient with widespread areas of tenderness, which you might think are tender points, but may, in fact, be insertion sites throughout the axial skeleton. That's kind of enthesitis that's the inflammatory arthritis.

And then back involvement, just like in axial spondyloarthritis, can also be difficult to pick out. So patients with back involvement, especially if they're older, may present non-specifically. They may not necessarily manifest with inflammatory back pain like we would typically think about in axial spondyloarthritis. And in fact, what we see is that in patients with psoriasis and suspected psoriatic arthritis, the typical criteria we think of for inflammatory back pain is less reliable. Because the rate of spondylitis and sacroiliitis are considerably higher in this population, the sensitivity of the inflammatory back pain questionnaire is not nearly as high as it would be for a non-selected population when you're thinking about axial spondyloarthritis. And so a high index of suspicion is really needed to identify axial involvement or sacroiliitis in patient with psoriasis that present with back pain.

So all of this is a substantial challenge, and I haven't even gotten to differentiating it from other inflammatory arthritides. This morning, in the clinic, I had a patient who had sort of severe psoriasis, and by the way, high positive RF and CCP. And a question arises, is this inflammatory arthritis as he's experiencing RA, or is it PSA? And differentiating those two can sometimes be a real challenge, especially in people with more of a polyarthritic phenotype as opposed to monoarthritis, oligoarthritis, axial involvement, et cetera, and really requires attention to the other presenting features. So for example, does the patient have enthesitis? Does the patient have dactylitis? And when that occurs, you can rest a little bit more on your laurels that you probably have a diagnosis of psoriatic arthritis. But when it's just pure inflammatory arthritis, it can be a little bit more challenging to pick out. So, yeah, there are a lot of diagnostic challenges in this condition.

Even when you're quite sure that this is psoriatic arthritis, we still struggle sometimes with monitoring of disease activity. Is the patient who has psoriatic arthritis currently on a biologic. Their peripheral arthritis is controlled, but they have back involvement. Is that back pain because of their psoriatic arthritis? Or is this a superimposed mechanical injury? So you know, even once the diagnosis is made, monitoring of disease activity can be challenging.