Validation of a modified version of the Brief Pain Inventory for painful diabetic peripheral neuropathy

Neuropathic pain is the focus of current clinical research, clinical identification, and treatment. It is unique from nociceptive pain and requires evaluation of the relevance and utility of common pain measures created for other painful conditions. This study evaluated the psychometric properties of a modified Brief Pain Inventory (BPI) for patients with painful diabetic peripheral neuropathy (BPI-DPN). Participants were patients with painful DPN (n = 255) enrolled in a DPN Burden of Illness survey referred through 17 outpatient settings (primary care physicians, endocrinologists, neurologists, and anesthesiologists). Patients completed the BPI-DPN and self-report measures of health-related quality of life, mood sleep, and health care use. Construct, criterion and discriminant validity, and internal consistency reliability were evaluated. Principal axis factoring with oblimin rotation revealed two interpretable factors (eigenvalues > 1.0), consistent with most published BPI validation studies: a severity scale comprising the four BPI Severity items and an interference scale comprising the seven Interference items, which satisfied criteria for interpretability and model fit. Cronbach's alpha was high (0.94) for both scales. Mean pain Severity was highly correlated with Bodily Pain from the Medical Outcomes Study Short Form-12, version 2 (r(s) = 0.63, P < .001), the Pain/Discomfort item in the Euro-QoL (r(s) = 0.58, P < .001), and a verbal rating scale measure of pain severity (r(s) = 0.74, P < .001). Individual BPI-DPN Interference domains were moderately correlated (r(s)'s > 0.5, P < .001) with analogous measures, and the Sleep Interference item had a high, significant association with the three primary Medical Outcome Study-Sleep scale subscales (r(s)'s = 0.66-71, P < .001). Worst Pain and Interference ratings were significantly associated with hospital use and outpatient visits because of DPN. These results replicate, in a pure peripheral neuropathic pain condition, the BPI psychometric characteristics documented in populations with nociceptive or mixed pain conditions. The BPI-DPN is a promising instrument in the evaluation of painful DPN.