Diagnosis of Psoriatic Arthritis



Anthony M. Turkiewicz, MD:John, in your clinical practice, are there any tools that you use to diagnose? There are obviously physical exam findings, histologies, and imaging.

As we go over clinical trial data about the CASPAR [Classification Criteria for Psoriatic Arthritis] criteria, what role does that play in the clinical setting outside clinical trials in your diagnosis algorithm?

John Tesser, MD: Let me put this in the context of what we do in a drug study with patients. I go into an exam room with my coordinator to do the psoriatic arthritis measurements, and I come out exhausted. I must do a full joint count. I must check all the entheses to do an enthesitis index. I must do a PASI [Psoriasis Area and Severity Index] score by identifying all the lesions in the general area and all the aspects of the skin, with the erythema and desquamation. Then I have to do the NAPSI [Nail Psoriasis Severity Index], which looks at all the nails and the pits, onycholysis, and desquamation, and the grumbling. You get the picture.

That’s what we do in a clinical trial. But when I’m seeing a patient in the clinic, I’m examining all the joints, unlike Steve who just can’t bear to think about doing something like that. I’m checking all the enthesitis areas.

Interestingly, after you’ve done this for many years, you can do this very quickly, but you do have to remember to pinch the Achilles tendons. Because if you don’t pinch them, you won’t actually elicit the tenderness that a lot of patients have and that they don’t realize that they have. You have to look at the toes, the fingers, and the skin. You can do this reasonably quickly, but you don’t measure it.

As far as blood work, we look at acute phase reactants with SED [sedimentation] rate and CRPs[C-reactive proteins]. We measure an HLA-B27 realizing that it doesn’t add that much in terms of the diagnosis. If it’s there and there’s a clinical suspicion for the disease, it supports the diagnosis. And if it’s not there, you know, not think about the diagnosis anymore.

Imaging is important, and certainly getting x-rays of hands and feet you can pick up subtle or major issues related to erosions, but also particularly new bone formation. Because that element right there distinguishes the radiological features of PsA vs RA [rheumatoid arthritis]. In RA you never see a bone formation. Consequently, that helps to make a distinction. That is 1 of the criteria for CASPAR in terms of diagnostic criteria.

But before I get to those, 1 last thing I want to say about imaging is that we have employed ultrasound in a systematic way. And ultrasound of the hands, and particularly the feet, is helpful. For our ultrasonographer, a person who reads the images, we have a technologist who does them. He picks up amazing things, and particularly for the tenosynovitis, and particularly in the feet and the Achilles tendon. That is invaluable because you don’t know what we’re missing when we’re doing a clinical exam.

That brings me to the discussion about the CASPAR criteria. Let’s remember these are classification criteria, they’re not diagnostic criteria. The only diagnostic criteria we have in rheumatology are the Jones criteria for rheumatic fever.

The CASPAR criteria are interesting because it’s a weight-based composite score, and you weigh different components. The element that is the most critical and the most important is that before you apply the criteria, the patient must have, on examination, an element of inflammatory musculoskeletal issue. That’s either synovitis, enthesitis, or dactylitis. If they don’t have that, at some point during your examination, or if you’ve seen them over a period of time, you can’t utilize the criteria. That’s the stopping point.

If they have it, then you start looking at whether they have skin involvement. Right then and there, psoriasis to get a couple of points. If they have enthesitis, they get a point; nail disease, a negative rheumatoid factor; and new bone formation on an x-ray.

Then you add up the points. If they have 3 points or more, they have met the criteria for the CASPAR classification. Now what’s the importance of that? That person would be able to go into a clinical trial. If someone doesn’t meet the criteria, that doesn’t mean they don’t have a disease, as Hillary [Norton] pointed out. It can be very tricky, very subtle, and therefore, you can make a clinical diagnosis on the basis of what you have in front of you, but you may not be as sure about it if they don’t have many of these clinical clues.

These criteria, classification criteria, like any classification criteria, act as a guideline. They act as something against which you take the elements and you can apply them to any patient you see, then at the end of the day you make your clinical judgment as to what’s going on.

Anthony M. Turkiewicz, MD: With the CASPAR criteria, as you point out, sometimes it’s not recognized or mentioned. But as you point out, there are joint-, entheseal-, and spine-based inflammatory processes. One of those must be ongoing to be part of the CASPAR criteria. As you said, the diagnostic strategy pointed out what you do in a clinical trial is helpful. You walk out exhausted doing these trials, but over time—even outside clinical trials—there are things you can do in a fairly regimented fashion.

Transcript Edited for Clarity

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