A Divorce Between Psoriatic Arthritis and Rheumatoid Arthritis

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At a dinner symposium hosted by Novartis at the annual meeting, a panel of experts explained the irreconcilable differences between psoriatic arthritis (PsA) and rheumatoid arthritis (RA). The presentation, titled “PsA: Is It Time to Divorce from RA? Identifying Clinical Signs and Symptoms, and Gaining New Insights into Pathophysiology and Management,” highlighted the many important distinctions between PsA and RA—despite the fact that they can have similar presentation and have historically been treated the same.

Philip J. Mease, MD, of the University of Washington School of Medicine in Seattle, introduced the topic, stressing that PsA and RA are distinct diseases. PsA often goes undiagnosed, he said, but early diagnosis is important to outcomes.

Distinguishing PsA from RA
Grace C. Wright, MD, PhD, president of the Association of Women in Rheumatology, said, “The divorce actually happened a long time ago, we just have to get with the program.”

PsA is part of the spondyloarthritis group of diseases, and she outlined its specific clinical hallmarks, in comparison with RA:

  • PsA involves the axial skeleton and distal interphalangeal joints, as opposed to the metacarpophalangeal joints and wrist joints in RA.
  • PsA can be mono-, oligo-, or polyarticular, as opposed RA, which is polyarticular.
  • PsA joints are often asymmetrical, whereas RA joints are mostly symmetrical.
  • PsA leads to enthesitis, but RA does not.
  • Dactylitis is a hallmark of PsA, but it is rare in RA.
  • Patients with PsA do not have a high titer rheumatology factor, as opposed to those with RA.
  • PsA often leads to nail lesions, as opposed to RA.
  • PsA involves psoriasis, which can appear before other signs and symptoms; RA does not.

“When we look at PsA, we are not just looking at joints,” Dr. Wright said, adding that innate and adaptive immune responses contribute to the pathogenesis of both PsA and RA, but RA joints are enriched with a range of inflammatory cytokines. In PsA, there is inflammatory activation at multiple sites, and PsA joints are enriched with interleukin-17-producing cells. Therefore, “Even if they look the same at presentation, we have to look at the activation to understand and treat.”

If left untreated, PsA can have a significant impact on patients’ functional status and quality of life, she said. Because of some of the disease manifestations, patients often are seen by their primary care physicians and specialists such as dermatologists long before they are referred to rheumatology.

PsA’s Impact on Patients
Dr. Mease focused his presentation on PsA’s effects on patients’ lives. Peripheral arthritis can lead to irreversible deformities, pain, stiffness, and loss of function, he said, and the damage is progressive in most patients.

Enthesitis, he continued, also has a significant impact on patients, who report diffuse aches and pains and often present with a swollen joint or digit but have endured months or years of pain and tenderness. Importantly, he said, the presence of enthesitis is a biomarker of increased disease severity and poorer functional status. Its true prevalence is underestimated, because it may mimic mechanical stress injury or tendonitis, and quantification by physical examination is difficult due to the location of the sites. Dactylitis is also a marker of disease severity, Dr. Mease said—if it is present, it is associated with greater disease burden.

Spine disease is present in 50% of patients with PsA, he continued, but presentation is variable. Patients with this manifestation have poorer physical function and health-related quality of life (HRQOL) than patients with more peripheral involvement. However, about 20% of patients with evidence of axial involvement may not be symptomatic, he said.

Regarding the skin, even a moderate amount of psoriatic skin involvement is associated with greater disease burden, greater reported pain, fatigue, impairment, discomfort, and self-consciousness. Therefore, it is very important to acknowledge the skin with patients and evaluate its involvement. In fact, psoriasis often develops into PsA. Nail disease is also important, for similar reasons, but it is difficult to treat. Like the skin, nail psoriasis is closely associated with PsA development.

Assessment of PsA
Dr. Mease discussed PsA assessment tools but stressed that “one size does not fit all.”

For clinical trials, he said researchers should assess every item in the inner circle of the OMERACT (Outcome Measures in Rheumatology): musculoskeletal disease activity (including peripheral joints, enthesitis, dactylitis, and spine symptoms), skin diseases activity, and pain. Global assessment, physical function, HRQOL, fatigue, and systemic inflammation.

He said the American College of Rheumatology 20 Criteria tend to be the primary endpoint in PsA studies and has served researchers reasonably well in deciphering between treatment and placebo, but new composite measures are being developed to better elucidate disease severity and treatment effectiveness. They are being used more commonly in trials but not quite ready for use in clinical practice, he added.

Finally, Dr. Mease said, “No patient who comes to see you with this disease will be like another patient with the same disease. Take into account the different disease domains for individualized diagnosis and management,” referring attendees to guidelines created by the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (otherwise known as GRAPPA).

Practical Use of Imaging
Clinical examination may not provide an accurate or complete picture of PsA, said presenter Catherine J. Bakewell, MD, RhMSUS, of Intermountain Medical Group in Salt Lake City, Utah. She offered many images from her practice to demonstrate how imaging can help with diagnosis, proper prognosis, and better disease management.

The main modalities to visualize disease activity in PsA are radiography, ultrasound, and magnetic resonance imaging (MRI). Although radiography is fast, inexpensive, and reproducible, it cannot help researchers or clinicians visualize soft tissue or active inflammation, Dr. Bakewell said. MRI can show peripheral arthritis, enthesitis, dactylitis, and nail effects, and it is effective in detecting early disease. However, it cannot detect axial disease and is expensive. Therefore, she recommends ultrasound, which can detect all of those manifestations, including joints during movement, at a low cost.

In the future, researchers and clinicians may find themselves using new imaging modalities—even artificial intelligence—to diagnose, assess, manage, and monitor patients with PsA.

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