Clinical outcomes measurement: Use of BPI interference measures for assessing change in impact of pain

Abstract

To evaluate changes in the impact of pain among osteoarthritis (OA) patients, the Brief Pain Inventory (BPI; Cleeland, 1985), a well-validated measure of cancer pain, was investigated. Specifically, the seven-item pain-related interference with functioning subscale and sleep-interference item were examined using data from two clinical trials of pain medications. Study 1 included patient-reported “number of night awakenings with pain” and “quality of sleep,” in addition to the BPI; Study 2 included the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC; Bellamy, Buchanan, & Goldsmith, 1988). Intraclass correlations of 0.75 and 0.63 for the Interference subscale for Study 1 (N=133) and 2 (N=107), respectively, and 0.56 and 0.52 for the sleep-interference item denoted adequate test-retest reliability. Moderate-to-large Guyatt's statistics (0.46 to 1.14) provided strong evidence of responsiveness and demonstrated that the treatment effects, as assessed by the two measures of pain impact, were considerably larger in the treatment than placebo arms. Correlations further confirmed the validity of the two measures. In Study 1, “night awakenings with pain” was positively correlated with the BPI score (r=0.36 to 0.47, p<0.0001) and sleep item (r=0.55 to 0.57, p<0.0001) and both correlated negatively with “quality of sleep” (r=–0.72 to –0.53, p<0.0001). In Study 2, a single WOMAC item — pain experienced “at night while in bed” — correlated higher with the sleep-interference item (r=0.55 to 0.86, p<0 .0001) than with the BPI interference score (r=0.42 to 0.68, p<0.0001), confirming that pain “at night while in bed” is more closely connected to the extent that pain disrupts sleep than other activities. This study supplements previous validation efforts and experience with the BPI, confirming the ability of its Interference subscale and sleep-interference as useful measures of response to pain treatment in OA patients. The support of Purdue Pharma L.P. is gratefully acknowledged.