Hitting the Target in Psoriatic Arthritis: Which Outcome Measures Are Best?

Experts are still debating the utility of a unidimensional composite score compared with a multidimensional score for the assessment of disease activity in psoriatic arthritis.

Initially developed for use in patients with diabetes and other chronic diseases, treat-to-target strategies now represent the standard of care in several rheumatic and nonrheumatic diseases. A treat-to-target approach for patients with psoriatic arthritis (PsA) was first recommended by the European League Against Rheumatism in 2015, based on results from the Tight Control of Psoriatic Arthritis (TICOPA) trial (ClinicalTrials.gov identifier: NCT01106079).1,2 In the trial, patients with PsA who received algorithm-determined treatment adjustments based on monthly assessments with an objective assessment of the minimal disease activity (MDA) criteria had significantly improved joint outcomes compared with patients who received standard care.2

However, the ideal instrument to use for the continuous assessment of disease activity in PsA has still not been definitively determined. This is partly because of a disagreement about whether to use a multidimensional approach, in which measures of multiple domains of disease activity are combined into a single composite score, or a unidimensional approach, in which each of the domains is scored separately.3,4

New consensus-based recom­mendations for physicians on the use of com­posite measures and treatment targets in PsA were recently issued by the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) and endorsed by the Outcome Measures in Rheumatology (OMERACT) group, using evidence on composite measures and potential treatment targets and surveys from healthcare professional members of GRAPPA and patients with PsA.5 GRAPPA/OMERACT reached a unanimous consensus that remission is the ideal conceptual target of treatment, as determined by the stringent very low disease activity criteria. MDA was chosen as an alternative target. The very low disease activity designation requires that 7 of the MDA criteria be achieved (tender joint count, ≤1; swollen joint count, ≤1; Psoriasis Activity and Severity Index, ≤1; tender entheseal points, ≤1; patient global disease activity visual analogue scale, ≤20 mm; patient pain visual analogue scale, ≤15 mm; and health assessment questionnaire, ≤0.5), whereas MDA requires 5 of the 7 criteria.2,5 MDA and very low disease activity are state measures that cannot be used to follow patients throughout their disease.

Although a number of continuous composite measures of disease activity were evaluated, GRAPPA/OMERACT did not reach a consensus on which to use. The PsA disease activity score received the highest number of votes for use in randomized controlled trials, whereas an average of scores on 3 visual analog scales comprising patient’s assessment of skin disease, patient’s global assessment of disease activity, and physician’s global assessment of disease activity received the highest number of votes for use in clinical practice.5 The report noted that “the majority of respondents thought that a single composite measure was more clinically useful than individual assessment of each domain, and they believed that such composites should include measures of arthritis, enthesitis, and dactylitis, markers of inflammation, and scores on patient’s global assessments.”

Another task force of rheumatologists, dermatologists, patients, and a healthcare professional convened in 2017 to update professional recommendations issued in 2012 on treat-to-target strategies for spondyloarthritis.6 Five overarching principles and 11 recommendations were issued, including a recommendation for clinical remission/inactive disease of musculoskeletal and extra-articular manifestations as a treatment target, with low or minimal disease activity as an alternative. They also issued a recommendation that “validated measures of musculoskeletal disease activity and assessment of cutaneous and/or other relevant extra-articular manifestations should be used in clinical practice to define the target and to guide treatment decisions.”

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Recommended measurements of disease activity for guiding the adjustment of therapy in a treat-to-target approach were Disease Activity index for Psoriatic Arthritis, a unidimensional measure that focuses on joint involvement, and MDA, although this position was not supported by all task force members.6 The authors noted that the question of whether unidimensional composite scores or multidimensional scores were best suited to assess disease activity in PsA was heavily debated. “Importantly, it was generally agreed that all manifestations of PsA needed to be assessed and that for each of the domains validated measures existed, but there was disagreement whether to bring them together into one score or evaluate them separately,” they wrote.

“PsA has many different manifestations,” Josef Smolen, MD, professor of internal medicine and chairman of the Department of Rheumatology, Vienna General Hospital, University of Vienna, and chairman of the 2nd Department of Medicine, Center for Rheumatic Diseases, Hietzing Hospital, Vienna, Austria, told Rheumatology Advisor. Dr Smolen was coauthor of the GRAPPA/OMERACT recommendations and lead author of the 2017 task force recommendations. “For each [manifestation], such as arthritis, skin involvement, or enthesitis, there are validated scores. Each of them is associated with different susceptibility genes. It is unknown whether they all have the same pathogenesis. If you use a unidimensional approach [by using] a validated score for each of the domains, you know exactly which of them is active and which one is not active. If you bring all the scores together into a single summary score, a multidimensional approach, you don’t know this. Therefore, you may have an excellent therapeutic response of the skin and little response of the joints, or vice versa.”

Dr Smolen pointed out that in the GRAPPA treatment recommendations approach, each domain is determined by a separate treatment algorithm. “So even by GRAPPA’s own therapeutic algorithms, multidimensionality is not favored.”

“Of course rheumatologists should choose the way they assess patients; therefore, they should not be forced to use multidimensional scores,” Dr Smolen stated. “On the other hand, they should use a score developed for PsA and validated in PsA.”


  1. Gossec L, Smolen JS, Ramiro S, et al. European League Against Rheumatism (EULAR) recommendations for the management of psoriatic arthritis with pharmacological therapies: 2015 update. Ann Rheum Dis. 2016;75(3):499-510.
  2. Coates LC, Moverley AR, McParland L, et al. Effect of tight control of inflammation in early psoriatic arthritis (TICOPA): a UK multicentre, open-label, randomised controlled trial. Lancet Lond Engl. 2015;386(10012):2489-2498.
  3. Helliwell PS, Coates LC. The definition of remission in psoriatic arthritis: can this be accurate without assessment of multiple domains?Ann Rheum Dis. 2015;74(12):e66.
  4. Schoels MM, Aletaha D, Smolen JS. Defining remission and treatment success using the DAPSA score: response to letter by Helliwell and Coates. Ann Rheum Dis. 2015;74(12):e67.
  5. Coates LC, FitzGerald O, Merola JF, et al. Group for research and assessment of psoriasis and psoriatic arthritis/Ootcome measures in rheumatology consensus-based recommendations and research agenda for use of composite measures and treatment targets in psoriatic arthritis. Arthritis Rheumatol (Hoboken). 2018;70(3):345-355.
  6. Smolen JS, Schöls M, Braun J, et al. Treating axial spondyloarthritis and peripheral spondyloarthritis, especially psoriatic arthritis, to target: 2017 update of recommendations by an international task force. Ann Rheum Dis. 2018;77(1):3-17.