Psychometric assessment of the Persian version of the patient determined disease steps scale in patients with multiple sclerosis and neuromyelitis optica spectrum disorder

Background: The purpose of this study was to evaluate the validity and reliability of the Persian version of Patient Determined Disease Steps (PDDS) in both patients with multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD). Methods: One hundred and forty-five patients were enrolled between May and September 2020 by consecutive sampling. Participants were asked to complete timed 25-foot walk (T25FW), 12-item Multiple Sclerosis Walking Scale (MSWS-12), and Multiple Sclerosis Quality of Life-54 (MSQOL-54). Patients also completed Timed Up and Go (TUG) and six-minute walk (6MW) tests. Construct validity was assessed by calculating correlation between PDDS and ambulatory and demographic items. The intra-class correlation coefficient (ICC) was used to evaluate reliability. Results: One hundred and eleven patients with MS and 34 with NMOSD with disease duration of 7.6 ± 5.8 years were enrolled. Twenty-seven percent were men and mean Expanded Disability Status Scale (EDSS) was 1.8 ± 1.8. There was a significant positive correlation between EDSS and PDSS (rho = 0.64, P < 0.001) which was evident in MS subgroups and NMOSD [secondary progressive MS (SPMS): rho = 0.64, P < 0.001; relapsing-remitting MS (RRMS): rho = 0.47, P < 0.001; NMOSD: rho = 0.52, P = 0.001]. PDDS had also significant positive correlation with TUG, T25FW, and MSWS-12. PDDS had also significant negative correlation with 6MW test. PDDS had weak correlation with demographic variables. The ICC was calculated as 0.99 for PDDS. Conclusion: The Persian version of PDDS provides valid and reliable instrument to assess MS/NMOSD-related disability.