Development and validation of the Diabetic Peripheral Neuropathic Pain Impact (DPNPI) measure, a patient-reported outcome measure.

ABSTRACT

PURPOSE: Diabetic peripheral neuropathy (DPN) occurs in 26-47 % of diabetes patients and may have negative impacts on physical functioning, sleep, well-being, and quality of life. The Diabetic Peripheral Neuropathic Pain Impact measure (DPNPI) was developed to measure disease impacts and treatment effects. Presented are the DPNPI conceptual development and validation findings. METHODS: The DPNPI was developed following the FDA Guidance for Industry on patient-reported outcome (PRO) measures. Concept elicitation (CE) included literature review, clinical expert interviews, and patient interviews/focus groups. Qualitative data were analyzed following grounded theory principles, and draft items were cognitively debriefed. The measure underwent psychometric validation, and an a priori statistical analysis plan assessed the measurement model, reliability, and validity. Simultaneous analyses of item functioning were conducted using Rasch measurement theory (RMT). All tests were performed for the total score and each domain. RESULTS: Twenty-five patients and three clinical experts participated in CE which resulted in a 27-item validation ready measure. In the validation study (N = 124), nine draft items were dropped due to high missing data and/or high correlations between items. Factor analysis revealed three domains physical functioning/mobility, sleep, and daily activities. RMT confirmed adequate item fit and placement within domains. Internal consistency ranged from 0.91 to 0.96 and test-retest from 0.84 to 0.91. All prespecified hypotheses for convergent and discriminant validity were met. CONCLUSIONS: CE and psychometric results provide evidence that the final, 18-item DPNPI is a reliable and valid PRO measure of disease impacts and treatment for DPNP. Further validation work should include responsiveness assessment.