Spanish adaptation of the Primary Lateral Sclerosis Functional Rating Scale (PLSFRS).

Objective: Primary Lateral Sclerosis (PLS) is a progressive neurodegenerative disease with no current therapy. So far, the lack of a specific evaluation instrument has been a barrier for clinical trials. The Primary Lateral Sclerosis Functional Rating Scale (PLSFRS) is a novel tool designed to specifically assess disease progression and functional impairment in patients with PLS. We sought to translate and validate the PLSFRS to the Spanish language. Methods: We back-translated the PLSFRS scale to Spanish and assessed a cohort of 10 PLS patients by two independent raters. Both inter- and intrarater reliability were evaluated, with assessments conducted through both in-person and over-the-phone interviews. Results: The PLSFRS demonstrated excellent inter- and intrarater reliability for the total score (ICC = 0.90-1.00) and for most subdomains (ICC > 0.90). Agreement between in-clinic and over-the-phone assessments was similarly strong. Squared weighted kappa coefficients for individual items indicated substantial to almost perfect agreement. Bland-Altman analysis revealed no significant systematic bias, with mean differences close to zero and acceptable limits of agreement. Conclusion: This study demonstrates high reliability for the Spanish version of the PLSFRS scale.