Clinical outcomes measurement: Classification of mild, moderate and severe pain due to diabetic peripheral neuropathy based on levels of functional disability

Abstract

This study identified discrete categories of pain severity in a sample of patients with painful diabetic peripheral neuropathy (DPN), through derivation of cut-points on a 0-10 scale of pain severity (modified Brief Pain Inventory-DPN, m-BPI-DPN). Cut-points are important for characterizing patients and outcomes and address nonlinearity in patients’ interpretation of numeric pain severity scales. We adapted the method of Serlin and colleagues that established cut-points for cancer pain severity based on interference with function. Since neuropathic pain is a unique condition, replication is appropriate. Subjects were participants in a burden of illness survey (N=255). Average and Worst Pain (m-BPI-DPN) were 5.0(SD=2.5) and 5.6(SD=2.8). We considered all possible cut-points between 4 and 8. Optimal cut-points were those that created three pain severity categories producing maximum between-category differences on the seven m-BPI-DPN Interference items, using MANOVA. Cut-points of 4 and 7 optimally classified the sample, creating categories of <4, 4 to <7 and 7 and higher, (Hotelling Lawley trace F = 22.95 and 16.20 for Worst and Average Pain, p<.0001). Those reporting pain <4 characterized their pain over the past month as “mild” or “very mild,” those with pain 4 to <7 generally classified pain as “moderate,” and those >∓ 7 generally classified pain as “severe,” confirming the terms mild, moderate and severe for the cut-point-derived categories. Mean m-BPI-DPN Interference was 2.1(SD=2.1), 4.9(SD=1.9) and 7.4(SD=1.6) for the mild, moderate and severe pain categories. Patients in the three categories differed on patient-rated outcomes (the SF-12v2, HADS, MOS-Sleep, p=.001), medication satisfaction (p<.01), and on mean DPN-related healthcare visits over the past three months (p<.01): 2.26(SD=3.43), 3.38(SD=7.86) and 5.53(SD=7.04). This research shows that three categories of DPN pain severity can be identified based on interference with daily function, and these categories influence patient outcomes and medical utilization. Research was supported by Pfizer, Inc.