Progression in psoriatic arthritis: role of time varying clinical indicators.

Objective: We have shown that the presence of 5 or more effusions and high medication use at first clinic visit predicted clinical progression in patients with psoriatic arthritis (PsA), while a low erythrocyte sedimentation rate (ESR) was "protective." These clinical indicators will change over the course of a patient's disease. We investigated whether there is additional prognostic information available through monitoring these indicators at each clinic visit.

Methods: A total of 365 patients with at least 2 followup visits at the PsA Clinic who did not have 10 or more damaged joints at first visit were included. Clinical assessments including the number of actively inflamed and damaged joints were carried out every 6-12 mo according to a standard protocol. The analysis used a generalized linear model that relates the number of damaged joints that developed between consecutive clinic visits to the information available at the first of the 2 visits, and in which the information was added to a baseline model including the first visit variables previously shown to be important.

Results: Single factor analysis suggested that the addition of functional class, number of actively inflamed joints, and Lansbury index provide prognostic information for subsequent damage. The final multivariate model includes time varying information on the number of actively inflamed joints, functional class, and current damage, as well as first visit information on prior medication as predictive of progression of damage, plus male sex and a low ESR at first visit as "protective."

Conclusion: Time varying predictors for damage are important and should be monitored longitudinally in patients with PsA.