Spondyloarthritis: Challenges in Diagnosis

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Philip J. Mease, MD, distinguishes the clinical features of spondyloarthritis, such as psoriasis, psoriatic arthritis, and inflammatory back pain, the challenges of each, and the diagnostic tools used.

Philip J. Mease, MD: It turns out that we have a perfect biomarker for the diagnosis of psoriatic arthritis, and that is psoriasis in the skin. In the great majority of patients with psoriatic arthritis, psoriasis will appear first—often as long as 10 years before the arthritis appears. And so it’s very important for dermatologists and their clinical staff to be aware that psoriatic arthritis can occur in their patients with psoriasis, and to be asking questions when they come into the clinic. Do you have any joint pain? Do you have any pain where ligaments are inserting into bone? That sort of thing. We’ve developed some simple questionnaires that dermatologists can employ in their practices in order to ascertain whether some of their patients may be beginning to develop psoriatic arthritis. That’s really the key thing from a population level identification of the disease.

Why is this important? Because we know that there are studies that have been done where we’ve ascertained if there’s a delay of diagnosis. In one study in Dublin, it was a delayed diagnosis of 6 months from onset of symptoms. In another study in Toronto, it was a delay of 2 years from onset of symptoms. Then there were the consequences of a delay in diagnosis. More damage, more functional disability, and more problematic features of psoriatic arthritis occurred in patients who had a delay of diagnosis. So, we are spending a lot of time trying to sensitize dermatologists and primary care clinicians about the importance of realizing that psoriatic arthritis can occur in patients with psoriasis.

It’s all the more important because sometimes some of the features are hard to distinguish from other forms of arthritis. For example, I already mentioned that in the case of osteoarthritis it can prominently present to the distal interphalangeal joints. In the case of degenerative arthritis of the spine, which is very common in the population, it may be hard to distinguish between run-of-the-mill back pain problems and the potential that this is the onset of psoriatic arthritis. So, these are some of the features that may be part of the presentation of a disease that are important to sensitize clinicians to understand it.

One of the problems of diagnosing both psoriatic arthritis and ankylosing spondylitis is the issue of back pain. Back pain is a very common problem in humans. It’s one of the more common issues that we face during our lifetime, usually because of degenerative spine disease, disk problems—mechanical back pain as it’s called—or sometimes as a condition of a fibromyalgia. These are very common in the population. Psoriatic arthritis and ankylosing spondylitis are less common.

And so the first thought that many clinicians have when they hear a patient describing back pain is, “Oh, this is run-of-the-mill back pain or fibromyalgia.” They don’t even think about the possibility that it could be an inflammatory spondylitis, which is the presenting manifestation in patients with ankylosing spondylitis typically, and sometimes a prominent manifestation of psoriatic arthritis. So, first of all, we have to be aware of this as a potential reason for back pain, and then be sensitive to what the features are that help define inflammatory back pain. The fact that the pain gets worse with rest and gets better with activity, that’s a key distinguishing feature from degenerative spine disease. Or sometimes an individual will describe that they wake up in the middle of the night because of back pain and have to get up and walk around to relieve it. That’s very characteristic of inflammatory back pain.

The other feature is that it typically starts out in the younger years. So, if you’ve got back pain that starts out before the age of 40 and it’s persistent, then that increases the likelihood that it could be an inflammatory spondylitis. Both for ankylosing spondylitis and psoriatic arthritis, these are some of the key features that we need to be sensitive about in identifying the possibility that it’s immunologic disease.

As we begin to talk about laboratory and imaging, and diagnosing and monitoring psoriatic arthritis, one comment that I’ll make is that really the best way of diagnosing the disease is through history and a physical. Studies have shown that one can be very accurate just using simple historical questions and physical exam techniques. But if that doesn’t really help you adequately in assuring the diagnosis, then we do use laboratory imaging to support our diagnosis. So, for example, we might use CRP (C-reactive protein) or sedimentation rate. And if those are elevated, those can help us understand that inflammation process may be present.

We’ll sometimes test for autoantibodies to potentially rule out other conditions. For example, if a person has very high levels of rheumatoid factor antibody or CCP (cyclic citrullinated peptide) antibody, this may point toward rheumatoid arthritis being the diagnosis. Having said that, we know that some people with psoriatic arthritis may have a positive rheumatoid factor or CCP. So, this is not an absolute.

In terms of imaging, there are a number of approaches that we can take. There are characteristic changes in peripheral joint x-rays that can be seen, although this may be a late finding. MRI and ultrasound are much more sensitive in picking up changes suggesting synovitis and enthesitis in peripheral areas like the hand, wrist, and so forth. And in the spine, if we are suspicious of spondylitis being present in the psoriatic patient, then we use MRI imaging—especially in the sacroiliac (SI) joints—to look for evidence of bone edema adjacent to the SI joints, or narrowing or erosive changes of the SI joints. And also we can look at the spine itself to look for evidence of bone edema characteristic of an inflammatory disease.

Ultrasound is becoming a more and more commonly used technique in rheumatology practice. We can actually employ it right there in the exam room. We can look at multiple joint areas or enthesis areas. It does take the skill-trained person to know how to interpret the ultrasound. But it can be very helpful, not only for diagnosis of the condition, but also for monitoring whether or not we are adequately controlling the inflammation, as can, for example, following CRP in the 40% or 50% of patients with psoriatic arthritis who may have elevated CRP at the onset of their disease before we really have adequately treated it. And then we monitor the CRP over time.