Definitions of low disease activity or remission in patients with psoriatic arthritis that come from validated disease activity instruments identify different levels of residual disease despite having significant overlap. This level of variation between instruments can leave patients with residual disease that can affect their quality of life, researchers reported.
Treatment recommendations from the European League Against Rheumatism (EULAR) and the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) advise aiming “for remission or the lowest possible disease activity in all involved domains of the disease,” but they do not specify a target or instrument to be used to define either low disease activity or remission, wrote Laura Coates, MD, of the University of Oxford (England) and her coauthors. To look at the variation produced by existing instruments to measure those states, they applied a variety of scoring indices to a group of 250 psoriatic arthritis patients who were considered by their treating rheumatologist to have quiescent disease.
The investigators tested the Disease Activity Index for Psoriatic Arthritis (DAPSA), minimal disease activity (MDA) criteria, and the Psoriatic Arthritis Disease Activity Score (PASDAS) in the group of patients, who were required to have been on stable treatment for at least 6 months (Ann Rheum Dis. 2017 Oct 28. doi: 10.1136/annrheumdis-2017-211998).
The cut points they used to measure remission included a score of 4 or less for DAPSA and the clinical DAPSA (cDAPSA, which doesn’t use C-reactive protein [CRP]), and a state called very low disease activity (VLDA) in which all seven MDA domain cut points were met. “Near remission” on the PASDAS was a score of 1.9 or less.
Low or minimal disease activity was defined by DAPSA of 14 or less, cDAPSA of 13 or less, or meeting the cut points for a combination of different MDA domains, including one in which any five of the seven cut points are required to be met (“MDA 5/7”), one where both the tender and swollen joint count cut points are required to be met with any three of the remaining five cut points (“MDA joints”), one where the skin domain is required to be met along with four of any of the remaining six (“MDA skin”), and one where both the joint and skin domains need to be met with any two of the remaining four domains (“MDA joints and skin”).
Little is known about whether the disease activity composite scores of the DAPSA and PASDAS reflect the same clinical disease activity on the various MDA disease domain combinations, Dr. Coates and her associates said.
The results of the analysis showed that VLDA and PASDAS were the most stringent scores for remission and that the DAPSA and cDAPSA scores were the least stringent target for remission. For example, in the entire cohort, 107 (43.7%) patients fulfilled DAPSA remission, 113 (45.7%) were in cDAPSA remission, 56 (22.5%) met VLDA criteria, and 37 (19.5%) were in PASDAS “near remission.”
All patients who met VLDA criteria were in DAPSA/cDAPSA remission. Of those patients in DAPSA remission but not in VLDA, 43 of 56 patients did not fulfill one of seven domains, while nine did not fulfill two of seven domains. Domains not fulfilled were skin (n = 33), tender joints (n = 7), swollen joints (n = 1), enthesitis (n = 3), visual analog scale scores (n = 6), or Health Assessment Questionnaire (n = 9).
“Residual skin disease was highest in patients achieving DAPSA or cDAPSA remission … this resulted in a group of patients, seen as in a low disease activity state, with the remaining skin disease impacting their quality of life,” the investigators wrote. This analysis “highlights the need for multiple separate measures for different domains to be assessed if a multidimensional definition is not used to ensure that remission retains face validity for the patients.”
The addition of the inflammatory marker CRP in both remission and low disease activity measures (in DAPSA and PASDAS) did not have added value, suggesting that “the inclusion of CRP is unnecessary [since] a similar proportion of patients have a raised CRP in all definitions. … A target without an inflammatory marker will be more practical in clinical practice,” they said.
However, Dr. Coates and her colleagues stressed that the cut-off for acceptable disease activity is important because a stricter target may encourage the overtreatment of patients, which would result in increased side effects and costs.
“The ideal stringency of a target with assessment of residual disease in the various clinical domains of psoriatic arthritis should be a focus of research,” they wrote.
The original cohort of patients was supported with an unrestricted grant from Pfizer. Dr. Coates did not declare any conflicts, but several of her coauthors declared receiving speaker or consultancy fees from the pharmaceutical industry.