How do changes in pain severity levels correspond to changes in health status and function in patients with painful diabetic peripheral neuropathy?

The current analysis compares changes in pain with changes in function and health status in individuals with painful diabetic peripheral neuropathy (DPN). The post hoc analysis is based on a 12week, multinational, placebo-controlled trial of pregabalin in which 401 patients were randomized to treatment. Study measures included the Brief Pain Inventory short-form (BPI-sf), EQ-5D and other patient-reported outcomes. Cutpoints were derived on the BPI-sf 0-10 average pain numeric rating scale NRS to classify pain grades of "mild" (1-3), moderate (4-6) and severe (7-10), adjusting for geographical regions where data were collected. Two different metrics were used to classify the importance of change in pain severity from baseline to 12weeks: changes in pain severity grades (defined by cutpoint categories) and percent reduction in the NRS (categories ranging from 0-9% to 50%). An improvement in one pain grade or a 30% reduction in the NRS served as determinants of a clinically important difference. Patients with a one-grade reduction in pain severity, either from "severe-to-moderate" or "moderate-to-mild," had a 3-point improvement the BPI-sf Pain Interference Index (PII; a composite measure of function); a reduction from "severe-to-mild" pain corresponded to a 6-point improvement in the PII. Similarly, a reduction in the NRS of 30% and 50% corresponded to a 3-point and a 5-point improvement in the PII, respectively. Changes in pain were also associated with changes in health status. Results suggest that patients whose pain is not reduced to a mild level of severity can still experience clinically important changes in function and health status.