Role of clinical and biochemical inflammation in structural progression of patients with psoriatic arthritis

Objective To determine the contribution of clinical and biochemical inflammation to structural progression of patients with psoriatic arthritis (PsA). Methods We analysed patients from the Infliximab Multinational Psoriatic Arthritis Controlled Trial 2 trial (infliximab vs placebo). We obtained total modified Sharp/van-der-Heijde Scores from baseline and year one images, and swollen joint counts (SJC) and levels of C reactive protein (CRP) throughout the second half of year 1 (5 measurements) from 74 placebo-treated patients. We computed radiographic progression, time-averaged SJC (taSJC) and CRP (taCRP) values and assessed their impact on structural progression by logistic regression analysis. We further categorised patients as 'active' (+) or 'inactive' (-) based on their taSJC (cut-off point: 2/66 joints) and taCRP (cut-off point: 0.5 mg/dL) and compared radiographic progression across three groups (double inactive, single active, double active). Results ORs for progression were 1.24 (95 % CI 1.04 to 1.47; p=0.016) for taSJC and 6.08 (95 % CI 1.12 to 33.03; p=0.036) for taCRP. When predictors were dichotomised (+ vs -), differences were maintained between taSJC+ and taSJC- patients (1.05 +/- 3.21 and 0.56 +/- 2.30, respectively), as well as for taCRP+ vs taCRP- patients (1.14 +/- 3.23 and 0.05 +/- 2.37, respectively). Progression was intermediate in the presence of abnormalities of one but not the other inflammatory variable, indicating increasing radiographic progression with increasing inflammation (p=0.05). Conclusion In patients with PsA, both clinical and biochemical inflammation have an impact on structural progression. Overall, progression is smallest in the absence of both clinical and biochemical inflammation, higher when either clinical or biochemical inflammation is present and highest with both clinical and biochemical inflammation.