Processing speed test: Results from a Japanese normative sample of healthy participants compared with a US normative sample

Background: The Processing Speed Test (PST), a validated iPad & REG;-based cognitive screening test for MS, has been applied to the cognitive assessment of Japanese MS patients using US normative data.Methods: To develop PST normative data from Japanese healthy volunteers and compare the PST score distribution between Japanese and US healthy volunteers, 254 healthy Japanese-speaking volunteers were enrolled and stratified by age (20-65 years). Potential participants with a Mini-Mental State Examination score < 27 were excluded. PST raw scores (total correct) were from the Japan cohort and compared with age-restricted US normative data and propensity score-matched data created by matching sex, age, and educational level from a published study of 428 healthy participants. PST score distributions and standardized z-scores were compared using t-test and Kolmogorov-Smirnov test statistics.Results: The mean age of the Japan cohort was 44.1 years. The PST scores of Japanese volunteers were significantly different from those of the age-restricted (mean & PLUSMN; SD 61.8 & PLUSMN; 10.1 vs 53.7 & PLUSMN; 10.8; p < 0.001) and the propensity score-matched US cohort (62.1 & PLUSMN; 10.1 vs 53.3 & PLUSMN; 10.6; p < 0.001).Conclusion: Regression analyses centered on US normative data could underestimate disease severity in Japanese MS patients, suggesting that separate normative data should be considered for each population sample.