The Finnish version of The National Institutes Of Health Chronic Prostatitis Symptom Index correlates well with the visual pain scale:: translation and results of a modified linguistic validation study

OBJECTIVES To provide a fluent and easily comprehensible Finnish version of the National Institutes of Health Chronic Prostatitis Symptom Index (NIH-CPSI) and to study its linguistic validity and correlation with a visual pain scale (VAS). PATIENTS AND METHODS The double-back translation method with two interim modifications was used to produce the Finnish version of the NIH-CPSI. The validity was tested by presenting the questionnaire to 155 men with clinically confirmed chronic pelvic pain syndrome (CPPS) and 12 controls with no previous urological symptoms. Convergent validity of the NIH-CPSI was tested by determining the correlation between the Finnish NIH-CPSI and VAS. Patients' and urologists' opinions about the utility of the Finnish NIH-CPSI were also reviewed. RESULTS The total Finnish NIH-CPSI scores and the pain domain and voiding symptom domain scores differed significantly (P < 0.001) between the groups, suggesting good discriminant validity of the symptom index. The NIH-CPSI scores correlated well with the VAS (Pearson's correlation 0.76). The preciseness and comprehensibility of the questionnaire were consistently evaluated to be 'good' or 'excellent' both by patients and urologists. CONCLUSIONS The Finnish version of the NIH-CPSI is valid and easily comprehensible for measuring CPPS symptoms. In addition, it provides good discriminant and convergent validity in distinguishing CPPS symptoms and should be used as primary outcome measure in CPPS studies.