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Abstract
Introduction The PGA is a SLE outcome measurement reflecting the physician’s assessment of a patient’s disease activity. It is considered a ‘gold standard’ and contributes to responder indices for clinical trials, as well as to definitions of the low lupus disease activity state (LLDAS) and remission. Although a few studies have evaluated its sensitivity to change, no studies have assessed its minimal clinically important difference (MCID). Our objective was to determine the MCID of the PGA using prospective data collected in a single center.
Methods PGAs were scored prospectively by 3 physicians on consecutive patient visits; the difference between a visit PGA and the previous visit’s PGA was the ΔPGA. A disease flare visit was defined as a visit in which therapy was increased (initiation or increase of corticosteroid dose and/or DMARD or biologic agent). We constructed a receiver operating characteristics (ROC) curve to visualize the performance of the ΔPGA for predicting flare and determined the MCID of the PGA for flare using an anchored approach by calculating Youden’s index for the ΔPGA in 0.1 increments.
Results Data from 129 patient visits with ΔPGA and therapeutic decisions (therapy increase/flare or therapy decreased or no change/no flare) were available. The baseline PGA was between 0- 0.9 in 79 visits, 1.0-1.9 in 38 visits and between 2.0-3 in 12 visits. Flare occurred in 85 visits while no flare occurred in 44 visits with 43 (50.6%) of flares occurring with a baseline PGA between 0-0.9, 30 (35.3%) with a baseline PGA between 1-1.9 and 12 (14.1%) flares with a baseline between 2-3. The ROC curve for the performance of ΔPGA in predicting flare is shown in figure 1. The area under the curve was 0.774 (SE .034), p<0.001. A ΔPGA of 0.3 is associated with the highest Youden’s index.
Receiver Operating Characteristic (ROC) curve of ΔPGA for predicting flare. AUC = Area under the curve.
Conclusion Preliminary results from this small observational study suggest that the MCID for the PGA is 0.3. Larger studies evaluating the ΔPGA and flare, scored by multiple physicians are necessary.
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