Optimal Management of Rheumatic Disease During COVID-19 - Episode 6

Accurately Diagnosing Psoriatic Arthritis

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Philip J. Mease, MD: The most common reason for referral to us of a patient with psoriatic arthritis is from a dermatologist who has been seeing the patient for their psoriasis and has picked up that the patient has pain or swelling in a joint, swelling in a whole digit, or other pain complaints. For whatever reason, the dermatologist has asked the patient about it because they know the importance of screening for psoriatic arthritis or because the patient has just brought it up and said, “Hey, Doc, what do you think about this swollen digit?”

When we see the patient, 1 of the interesting things is that they will often remember that their symptoms have gone back for some time, and sometimes it’s enthesitis but not arthritis that the patient remembers. For example, a difficult Achilles tendon pain problem, plantar fascia, or even chest pain because of the enthesitis in the rib cage. Enthesitis and arthritis bring the patient to our attention. A more difficult area for us to evaluate is back pain. The patient may either have back pain at the initial presentation of psoriatic arthritis or develop it later on. Sorting it out from a degenerative arthritis is often difficult.

All these things are what bring the patient to us, but if we dive further we find other symptoms. Fatigue is a very prominent issue, and sometimes the comorbidities are obesity, hypertension, or hyperlipidemia. For those we have to get on the patient to make sure they’re attending to them with their primary care physicians.

These are the ways in which we see these patients, and they typically have multiple clinical domainsoccurring. I’ve already alluded to several, in addition to skin and nail disease, and all of them significantly impact them in terms of function and quality of life.

Of course, history and a physical are how we make the diagnosis. One of the interesting things to support that point is that in the PREPARE study that we published in 2013, where in nearly a 1000 patients attending psoriasis clinics were seen by a rheumatologist, and 30% were noted to have psoriatic arthritis. It turned out that just doing the history and physical could, essentially, correctly diagnose virtually every patient. We were allowed to do additional lab and imaging, but it was only rarely that we would need to have that in addition. So the history and physical are key.

The nature of joint pain: Is there stiffness involved? Is the joint pain persistent and not evanescent? The distribution of joints that are involved: Is there evidence of enthesitis at the heel or around the knee? Is there evidence of back pain? Does the patient have evidence on exam of swelling in their joints or swelling of a whole digit characteristic of dactylitis? Do they have evidence of nail disease, which was 1 of the common coexisting cutaneous aspects with psoriatic arthritis? This really helps establish it.

In terms of laboratory, unfortunately there is no biomarker, like rheumatoid factor or CCP, that can help us make the diagnosis. In only 30% to 40% of patients, even with active psoriatic arthritis, was their acute phase reactant of SED [sedimentation rate] rate or C-reactive protein elevated. If they’re elevated and we see them change with treatment, then this can be a useful biomarker. But in many patients, this is not present. Imaging can be helpful, especially in our clinic. Advanced imaging with ultrasound looks for evidence of synovitis, for example, or enthesitis using gray scale. Power Doppler can be very helpful in making the diagnosis and contrasting the disease with osteoarthritis or even gout, which can be in the differential diagnosis, as well as rheumatoid arthritis or spondylarthritis.

The CASPAR [Classification Criteria for Psoriatic Arthritis] criteria is a classification system. It’s not intended to be diagnostic, although some clinicians will use it in that way, including dermatologists. The CASPAR criteria were published in 2006. It was a 4- or 5-year effort. Our center [Swedish Medical Center in Seattle, Washington] was 1 of the participating centers, and it came up with the following elements. If a patient has, in your opinion, synovitis or arthritis that is inflammatory in nature or enthesitis or spondylitis that is inflammatory in nature, then that’s the stem of the criteria. If this is met, then you can apply the rest of the criteria. If the patient currently has psoriasis, that gives them 2 points toward the necessary 3 to be classified as PsA [psoriatic arthritis]. If they have a negative rheumatoid factor, that gives them another point. Although we found in the CASPAR study that about 5% of PsA patients had rheumatoid factor positivity, so its positivity does not rule it out. If they have some nail changes or a few other features that will give them the points. The most common way of classifying them is with current psoriasis and a negative rheumatoid factor, and that gives a specificity of 99% and sensitivity of 93%, which is very good for classification criteria. In this way we classify patients to bring them into trials, but these are also useful questions to ask and examine patients as we’re looking for evidence of psoriatic arthritis.

Transcript Edited for Clarity