Innovations, challenges in PsA diagnosis
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Later diagnosis of psoriatic arthritis can considerably alter disease trajectory, but the disease’s subtle presentation poses a challenge to clinicians diagnosing it, according to Christopher Ritchlin, MD, MPH, professor and chief of allergy, immunology and rheumatology and director of the clinical immunology research unit at University of Rochester Medical Center.
“There have been studies showing that a delay of as little as 6 months in diagnosis can have a significant impact on the outcomes in terms of the severity of the disease and involvement of skin and joints, so early diagnosis has been shown to be very important and instrumental in improving outcomes,” Ritchlin said.
PsA occurs in about 30% of patients with psoriasis and increases its burden, with patients experiencing decreased quality of life, increased cardiovascular risk and higher health care costs. Still, an estimated 15% of dermatology patients with psoriasis have undiagnosed PsA.
Over the past 10 years, a more thorough understanding of PsA has helped clinicians in their diagnosis of the disease.
“I would say that the greater realization of the heterogeneous manifestations of psoriatic arthritis have helped clinicians to really look for these various subtle changes in patients when they do their history and examination,” Ritchlin said.
Clinically, PsA can present as distal (which presents alone in 5% of cases), oligoarticular, polyarticular, mutilans and axial/spondylitis.
“The realization that axial disease — meaning involvement in the back — is seen in up to 40% of patients is leading clinicians to really look for axial disease, both in their physical exam and imaging,” he said. “I would say that also the realization that there are a variety of forms of psoriasis that can be involved with arthritis has helped in the diagnosis.”
Tools in diagnosis
To assist in the diagnosis of spondyloarthritis conditions like PsA, clinicians have implemented imaging technologies such as radiography, ultrasonography and MRI.
“Ultrasound has been an imaging modality which we use frequently in our clinic, which is very helpful in identifying and confirming the presence of erosive disease in [patients’] joints, enthesitis, dactylitis,” Ritchlin said.
“It gives you a lot of information about joint inflammation, erosions, enthesitis, dactylitis, [and] has become a principal imaging modality in our practice,” he said. “We also do radiographs, but really ultrasound has added so many new dimensions to let us see the soft tissues and the bone and the entheses.”
Ritchlin noted that MRI is typically used in diagnosis of axial diseases, as it helps clinicians identify inflammation and bone marrow edema in patients with inflammatory back pain and in patients whose axial involvement is unclear.
“Axial [disease] is a real challenge, you can't palpate a joint or see swelling or put an MRI probe on a joint in order to tell you that that's inflamed,” he said. “The story is one of inflammatory back pain, but not all patients with inflammatory back pain have sacroiliitis.”
MRI can also help in diagnosing PsA in the distal interphalangeal joints, which could be mistaken for osteoarthritis, Ritchlin said.
“I would say that both of these imaging modalities have added new dimensions that can help us improve our diagnostic accuracy, and even in some cases provide some longitudinal evaluation,” he said.
And despite a lack of known PsA biomarkers, the biomarker human leukocyte antigen (HLA) B27 can assist in PsA diagnosis. Another SpA disease, ankylosing spondylitis, is more likely to develop in patients with severe sacroiliitis who are HLA B27 positive, so earlier diagnosis may be possible in these patients by detecting the marker. Looking for this biomarker may help identify PsA as well, Ritchlin said.
“Only a minority of patients who are HLA B27 positive have axial disease, but it gives you some insight,” he said.
Gaps in diagnosis, care
Despite advances in diagnosis, there are still obstacles in the way of appropriate care for patients with PsA.
“I think the disparities that we see in the rest of our health care system spill over into psoriatic disease,” Ritchlin said. “So, we know that patients that are in poor areas or in inner-city regions that their care may not be up to the kinds of care that we see in other communities.
“Then, of course, there's also the question of being able to provide biologic agents for patients that don't have the insurance coverage that will allow them to be able to take these medications, and this is a huge problem,” he said. “It's a huge problem in the working poor, it's a huge problem in our Medicare population, where they have trouble getting coverage for biologics, and this is an area that really needs attention in order to improve outcomes for patients with psoriatic disease.”
Another disparity in diagnosis arises with patients who have darker skin, who can have different disease presentations in the skin than PsA patients with lighter skin, Ritchlin said.
“I attended a conference recently where a dermatologist gave a really great talk showing pictures of how psoriasis can appear in dark-skinned patients,” he said. “And this is something we really need to get out to our clinicians, both in dermatology and rheumatology and in private practice, so they're able to identify the various forms of psoriasis in patients of color.”
Future of diagnosis
Researchers are investigating current diagnostic tools with the hope of creating more concrete criteria for being at risk for PsA, thus enabling earlier detection.
“I think that some of the studies we've been doing showing that patients that are at higher risk for developing psoriatic arthritis will have psoriasis and have ultrasound abnormalities, that may be a population that we can say is a higher risk to develop PsA,” Ritchlin said.
However, the main diagnostic method of interest is biomarkers.
“We’re all after the holy grail, which are biomarkers that we can measure in the sera, because it's easy to obtain that with a blood draw,” Ritchlin said.
Funded by a grant from the National Psoriasis Foundation, researchers are pursuing PsA biomarker development through several approaches, such as single-cell RNA-seq, metabolomic profiles, proteomics and spatial transcriptomics.
“I expect within the next 5 years, that we're going to see some of those emerge as really great opportunities to provide biomarkers we've not had before for diagnosis,” Ritchlin said.
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