Measuring Disease Activity in Psoriatic Arthritis

Psoriatic arthritis (PsA) affects an estimated 0.3% to 1.0% of the general population, and up to 42% of people with psoriasis.¹ Effective treatment requires adequate assessment of the various aspects of this multifaceted, widely variable disease. However, there is no consensus regarding which of the several available validated tools should be used to measure disease activity in clinical practice.

The Challenges

“There are several issues: Physicians do not routinely perform objective disease assessments regularly in any of our diseases, and whether this is due to time considerations, lack of training in the measurements, or absence of reimbursement is unclear,” explained Allan Gibofsky, MD, professor of medicine at Weill Medical College of Cornell University and attending rheumatologist and codirector of the Clinic for Inflammatory Arthritis at Hospital for Special Surgery in New York City.

In addition, there are no simple measures for joint activity in PsA, especially for axial disease, he told Rheumatology Advisor. Despite key differences between PsA and rheumatoid arthritis (RA), measures of disease activity for RA, such as the Disease Activity Score 28 (DAS28), have been commonly used in patients with PsA.²

The Goal

“It is first helpful to remind ourselves of what should be measured to adequately identify the clinical spectrum of PsA,” wrote William Tillett, MBChB, PhD, MRCP, a rheumatologist at the Royal National Hospital for Rheumatic Diseases, Upper Borough Walls, Bath, United Kingdom, who authored an editorial that appeared in the March 2017 issue of the Journal of Rheumatology.³ “It is well established that PsA is a heterogeneous disease affecting multiple disease domains including joints, entheses, spine, nails, eyes, and axial skeleton.”

In addition, there are various phenotypes of PsA, such as polyarthritis, asymmetrical oligoarthritis, mutilans, spondyloarthritis, and predominant distal interphalangeal arthritis, that patients may transition between over the course of the disease. These features of the disease can make assessment difficult.

Nonetheless, accurate assessment is important to define treatment targets and achieve optimal patient outcomes. “The routine use of validated disease activity measures, and validating or changing therapy based on the results of the disease activity score, coupled with a disease management plan, achieves better outcomes than a disease management plan alone,” according to Dr Gibofsky. “The treat-to-target strategy has become more commonplace in RA management, and should be used in PsA as well.”

Validated Tools

The International Group for Research in Psoriasis and Psoriatic Arthritis (GRAPPA) and the Outcome Measures in Rheumatology Clinical Trials (OMERACT) have identified tools that are appropriate for measuring PsA disease activity in clinical practice and trials.⁴ “Ideally, any composite measure should retain the ability to be broken down into its disparate domains…so that the effects of each of these individual aspects of the disease and their potential for differential treatment response can be assessed,” wrote the authors of a 2014 study that compared the “real-world” performance of frequently used measures of PsA disease activity.²

Common tools include the Composite Psoriatic Arthritis Disease Activity Index, the Psoriatic Arthritis Disease Activity Score, minimal disease activity, and the Disease Activity Index for Psoriatic Arthritis.

Although these measures have demonstrated strong concurrent validity and include many health domains, their complexity and the time required to administer them render them impractical for routine clinical use. Although the Disease Activity Index for Psoriatic Arthritis is relatively simple to compute, it does not include a skin assessment because this component failed to reach statistical significance in the studies in which the Disease Activity Index for Psoriatic Arthritis was developed.⁵

The GRAPPA further recommends that clinical assessments for PsA should ideally include patient-reported measures. The Psoriatic Arthritis Impact of Disease 12-item domain of health questionnaire is an innovative, recently developed patient-reported outcome. It consists of 12 physical and psychological domains, each with a different weight; pain, fatigue, and skin problems are considered to carry greater weight than other domains.

Responses to questions are based on a numerical rating scale from 0 to 10, and the final score also falls between 0 and 10, with a higher score indicative of worse activity. The Psoriatic Arthritis Impact of Disease 12-item domain of health questionnaire was validated in previous research, and a new study determined that it is appropriate for routine clinical use.⁶ The “main aim of a patient-derived [patient-reported outcome] in PsA is to identify the full burden on all the multifaceted disease domains of health,” wrote the authors.

Addressing Issues

To address other potential challenges, such as those pertaining to issues of time investment, training, and reimbursement, Dr Gibofsky suggests that various stakeholders including healthcare organizations, payers, and researchers consider the following actions:

 

• Demonstrate how routine and systematic measurement with a valid disease activity score will enhance clinical outcome, not just in cohorts but also in individual patients.
• Provide hands-on workshops and continuing medical education seminars to educate physicians and their supporting staff on the appropriate use of these measures.
• Treat the administration of these measures as a “procedure,” and reimburse for them.

Future research in this area should focus on the validation of additional disease activity measures that are easy to perform and can be administered routinely by the clinician. “Measures done as primary outcomes in clinical trials are not easily adaptable nor as meaningful in clinical practice,” Dr Gibofsky noted.

Summary and Clinical Applicability

Using disease activity scores for targeted treatment in PsA improves outcomes and should be used more often in routine clinical practice. Several validated tools are available, including newer ones that are easier and faster to administer and compute. 

References

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