What Should Be the Primary Target of “Treat to Target” in Psoriatic Arthritis?

Objective. Recommendations regarding “treat to target” in psoriatic arthritis (PsA) have stated that the target should be remission or inactive disease. Potential definitions include very low disease activity (VLDA), PsA Disease Activity Score (PASDAS) near remission, Disease Activity Index for PsA (DAPSA) or clinical DAPSA (cDAPSA) remission. Our aim was to investigate the proportion of patients who fulfill these definitions and how much residual active disease remained.

Methods. This analysis used 2 datasets: first, trial data from the Tight Control of PsA (TICOPA) study, which included 206 patients with recent-onset (< 2 yrs) PsA receiving standard and biological disease-modifying antirheumatic drugs (DMARD); and second, an observational clinical dataset from Italy of patients receiving biological DMARD. Proportions achieving each of the 4 potential targets were calculated in each dataset and comparisons between treatment groups were performed in the TICOPA dataset. Levels of residual disease were established for key clinical domains of PsA.

Results. All measures could differentiate the TICOPA trial treatment groups (p < 0.03). Lower proportions of patients fulfilled the VLDA criteria compared to DAPSA or cDAPSA remission. PASDAS results were different between the cohorts. Residual active disease was low across all definitions although higher levels were seen in DAPSA and cDAPSA compared to VLDA, particularly for psoriasis. In all measures, the proportion with elevated C-reactive protein was similar and low.

Conclusion. VLDA appears the most stringent measure. It ensures that significant active arthritis, enthesitis, and psoriasis are not present, in contrast with DAPSA and PASDAS, in which composite scores can “hide” active disease in some domains.