Identifying the minimum clinically significant difference in acute pain in the elderly

Study objective: To identify the minimum clinically significant difference in pain in elderly emergency department (ED) patients. Methods: This was an observational, prospective study of a convenience sample of patients aged 65 years or older with acute pain. Patients rated their pain on an 11-point numeric rating scale (NRS) on entering the study and every 30 minutes for 2 hours. The arithmetic minimum clinically significant difference was defined as the mean difference between current and preceding NRS scores when the subject described his or her pain as "a little less pain" or "a little more pain." The proportional minimum clinically significant difference was change in NRS in a 30-minute interval divided by the NRS at the beginning of the interval. We used generalized estimating equations to adjust for nonindependence of pain scores and to test trend over time. Results: One hundred ninety-five patients were enrolled (mean age 74 years; 73% women; 51% Hispanic; 33% black). The arithmetic minimum clinically significant difference averaged over all periods was 1.5 (95% confidence interval 1.3 to 1.6), the proportional minimum clinically significant difference was 25% (95% confidence interval 20% to 29%). The arithmetic minimum clinically significant difference unexpectedly decreased over time: 2.1 from baseline to 30 minutes, 1.4 from 30 to 60 minutes, 1.3 from 60 to 90 minutes, and 1.0 from 90 to 120 minutes (P<.001). In contrast, the proportional differences were more stable: 27% from baseline to 30 minutes, 22% from 30 to 60 minutes, 22% from 60 to 90 minutes, and 28% from 90 to 120 minutes (P=.89). Conclusion: The arithmetic minimum clinically significant difference in older ED patients was 1.5 NRS units and decreased over time, whereas the proportional change was 25% and more stable.