Validation of a Swedish version of the National Institute of Health - Chronic Prostatitis Symptom Index.

Chronic primary prostate pain syndrome (PPPS), usually referred to as chronic prostatitis with chronic pelvic pain syndrome (CP/CPPS), affects approximately 10% of all men. The National Institute of Health-Chronic Prostatitis Symptom Index (NIH-CPSI) was developed for clinical assessment and research evaluation of this patient category. The objective of this study was to translate the NIH-CPSI into Swedish, including cross-cultural adaptation and testing it for validity and reliability.  Material and methods: Fifty men with chronic PPPS participated in the testing of a new Swedish questionnaire. The initial translation included forward and backward translation followed by a comprehensive review by an expert committee. The preliminary Swedish translation was tested for face validity and test-retest reliability. In all steps of the translation, both medical experts and laymen participated.  Results: The Swedish translation showed a high degree of consistency with the original version. A few cultural adaptations were jointly agreed upon. The questionnaire was assessed to be clear to understand and having good face validity. The test-retest reliability showed an intraclass correlation (ICC) of 0.89 (95% confidence interval [CI] = 0.82-0.94) which indicates good to excellent reliability. The standard error of measurement and minimal detectable change were 2.5 and 7.0 respectively. A Bland Altman plot showed no systematic difference between test-retest.  Conclusion: This study brings to health care providers and researchers a Swedish version of the internationally recognised NIH-CPSI questionnaire having good validity and reliability, a beneficial addition in the management of men suffering from chronic PPPS in Sweden.