The definition of remission in psoriatic arthritis: can this be accurate without assessment of multiple domains?
Authors: Philip S Helliwell, Laura C Coates
Journal: Annals of the Rheumatic Diseases (2015)

The definition of remission in psoriatic arthritis: can this be accurate without assessment of multiple domains?We read with great interest the recent publication by Schoels et al 1 outlining response criteria and disease state cut-offs for the disease activity in psoriatic arthritis (DAPSA) score.The DAPSA is simple and quick to perform in clinic, making it feasible for use in clinical practice, but we remain concerned about these new definitions: first, we have major concerns about the limitations of just assessing the joints in such a heterogeneous condition; second, the development of these cut-offs was done entirely based on physician opinion, without any inclusion of patients' views; finally, there is a concern about response criteria developed almost exclusively within randomised controlled trial (RCT) datasets, which are not representative of the psoriatic arthritis (PsA) population as a whole.As stated in the paper, the DAPSA includes a number of key outcomes designated by the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis/Outcomes in Rheumatology Clinical Trials group, but does not cover them all.Currently, the key outcome measures recommended are peripheral joint disease, psoriasis, pain, global disease activity, function and quality of life. 2 The DAPSA covers just three of these.This is particularly concerning when developing definitions of remission for potential use in a treat-to-target strategy.Even in the expert survey where patients were classified into disease states, doctors were only given information included in the DAPSA.There was no information on entheseal, axial or skin involvement, which could radically affect expert's classification.In the discussion, the authors state that the exclusion of other musculoskeletal manifestations is a limitation, but that this is 'reasonable' 'given the relatively low frequency of entheseal involvement'. 1Most RCTs in PsA report enthesitis present in 25%-79% 3 4 of their patients, depending on entheseal indices used, and similarly high rates (79%) are seen in early PsA as seen in the Tight Control of Psoriatic Arthritis (TICOPA) study. 5ur principal concern is the development of definitions of disease state, particularly the definition of remission.Remission is a definite term implying absence of disease, 6 which is not accurate using these cut-offs as mild active joint disease could be present within the score of 4, and other aspects of the disease could be missed entirely with such a limited assessment.If this definition is used in a treat-to-target strategy, it could lead to dangerous undertreatment of patients due to misclassification.The authors suggest that other manifestations should be assessed separately, but in that case, and given the statistical advantage of composite measures, surely these outcome measures should be combined to create a definition of remission.There is always a difficult balance between comprehensive assessment of a variable disease and feasibility of outcome measures particularly in clinical practice.However, if the authors suggest that additional measures should be used for other disease manifestations then essentially they are advocating a composite disease activity measure, such as the Composite Psoriatic Disease Activity Index (CPDAI) or Psoriatic arthritis Disease Activity Score (PASDAS), which combines individual measures. 7 8The suggested combination with other outcome measures also reduces the feasibility of such a measure as the DAPSA as it still requires assessment (appropriately given the heterogeneity of the disease) of multiple domains, which will increase assessment time in clinic.