Psychometric features of Neuropathic Pain Symptom Inventory in Iranian people with Parkinson's disease.

OBJECTIVE Neuropathic pain is a type of pain reported in people with Parkinson's disease. There are various scales to evaluate the characteristics of this kind of pain. The purpose of this study was to investigate the psychometric properties of the Neuropathic Pain Symptom Inventory (NPSI), a specific scale that measures neuropathic pain in Iranian people with Parkinson's disease. METHOD Four hundred forty-seven individuals with Parkinson's disease were recruited in the study. Acceptability, internal consistency (Cronbach's alpha), and test-retest reliability (intraclass correlation coefficient, ICC) of NPSI were calculated. Dimensionality was examined through exploratory factor analysis. For convergent validity, correlations of NPSI with Douleur Neuropathic 4, Brief Pain Inventory, King's Pain Parkinson disease Scale, and Visual Analog Scale-Pain were used. Discriminative validity and sensitivity to change between On- and Off- medication states were analyzed. RESULTS A marked floor effect was observed for this scale (64.2%). Cronbach's alpha and ICC were 0.90 and 0.87, respectively. Items of NPSI were placed in 4 factors. A moderate to the strong association (rs = 0.55 to 0.85) between NPSI and other scales was obtained. The results of discriminative validity and sensitivity to change indicate the ability of NPSI to show differences between medication states. CONCLUSION The results of this study suggest that NPSI has acceptable reliability, validity, and sensitivity to change, indicating that this scale is suitable for measuring neuropathic pain in Iranian people with Parkinson's disease.