Objective: To describe patterns of systemic lupus (SLE) disease activity over time.
Methods: Disease activity was measured in a prospective cohort of 204 consecutive SLE patients followed up quarterly for 2.0-7.5 years (911 person-years of followup). Physician's global assessment (PGA) and modified SLE Disease Activity Index (M-SLEDAI; omitting serology) scores were plotted against time for each patient. Definitions for disease activity patterns were developed by consensus using these plots, and the proportion of total follow-up time represented by each pattern was calculated.
Results: Three patterns of SLE activity were apparent: relapsing-remitting (RR), chronic active (CA), and long quiescent (LQ). The CA pattern was the most frequent for both the PGA and M-SLEDAI, representing 58% and 40% of total person-years, respectively. The least common pattern was LQ (PGA 16%, M-SLEDAI 25%), while the RR pattern was intermediate in frequency (PGA 26%, M-SLEDAI 35%). Average disease activity during RR periods tended to be mild, while that during CA periods was more likely to be moderately severe. The most common discrepancy between instruments was that the PGA depicted CA when the M-SLEDAI showed an RR pattern. The M-SLEDAI did not appear to capture mild degrees of activity.
Conclusion: SLE activity was readily classified into 1 of 3 patterns: RR, CA, or LQ. The CA pattern was most common, suggesting that significant morbidity may arise from persistent disease activity. These findings may have important implications regarding the choice of outcome measures in SLE clinical trials, since comparison of flare rates may not account for chronic disease activity.