PsA is Not RA. So Why Use Those Criteria?

Acosta Felquer ML, Ferreyra Garrott L, Marin J, et al., Remission criteria and activity indices in psoriatic arthritis. Clin Rheumatol. 2014 May 13. [Online First ] doi:10.1007.s10067-104-262-sy.

While there are measures of disease activity specific to psoriatic arthritis (PsA), there are no standardized remission criteria for PsA. So gauges of activity and remission used in rheumatoid arthritis are often applied to PsA. But none really paint an accurate picture of PsA patients, according to Argentinean researchers.

A cross-sectional study of 55 consecutive patients comparing PsA-specific outcome measures with those used in RA show a wide variance in PsA patients judged to be in remission – as well as those who fit into the categories of low, medium or high disease activity.

In particular, the Disease Activity in 28 Joints (DAS28) of tender and swollen joints appears to be less stringent than other measures in assessing PsA. The Composite Psoriatic Disease Activity Index (CPDAI) showed the poorest correlation with other criteria, although the differences were not statistically significant.

The study assessed patients, most of them men in their 50s who’d had PsA for almost six years, using the CPDAI, the Psoriatic Arthritis Screening and Evaluation (PASE), and the Disease Activity Index for Psoriatic Arthritis (DAPSA), and three RA-centric indices, including the DAS28.

Judging by the Clinical Disease Activity Index (CDAI) and the American College of Rheumatology and European League Against Rheumatism (ACR/EULAR) remission criteria, only 9% of the study patients were in remission, compared to 33% of patients according to the DAS28.The  Simplified Disease Activity Index (SDAI) found the fewest patients in remission (4%) and the PsA-specific CPDAI found none, although it found 78%. The CPDAI found 78% of patients to have low disease activity.

The researchers point out that these indices are largely measures of joint inflammation, while they ignore components of PsA such as skin lesions, entheses, dactylitis, axial, and nail problems and the fact that arthritis and psoriasis may flare at different times.

If clinicians are going to take a treat-to target approach in PsA, the authors conclude, there’s urgent need for remission criteria for PsA.