Pre-diagnostic ALSFRS-R slope provides limited incremental information about the variability in subsequent functional decline in amyotrophic lateral sclerosis: a population-based study.

backgroundThe pre-diagnostic ALSFRS-R slope is frequently used in a clinical trial design and clinical practice under the implicit assumption that it reflects subsequent functional decline. We assessed the association between the pre-diagnostic ALSFRS-R slope and subsequent functional decline.

methodsThe Piemonte and Valle d'Aosta ALS Registry (PARALS) was used as the primary cohort. The associations between pre- and post-diagnostic slopes at 6, 12, and 18 months were examined using correlation coefficients and multivariable linear regression. Linear and quadratic mixed-effects models used all ALSFRS-R assessments obtained during the first 18 months to evaluate longitudinal trajectories and quantify the incremental contribution of the pre-diagnostic slope. All analyses were replicated in the Emilia Romagna Registry for ALS (ERRALS).

resultsA total of 2,222 patients from PARALS and 1,543 from ERRALS were included. In PARALS, the pre-diagnostic ALSFRS-R slope showed only a modest monotonic association with post-diagnostic functional decline (Spearman's ρ = 0.19-0.30) and explained 6.1% of its variance at 6 months, with this proportion decreasing thereafter. Quadratic mixed-effects models estimated that, at 12 months, the difference in ALSFRS-R change between patients in the highest and lowest pre-diagnostic slope quartiles was 2.04 points in PARALS (95% CI 1.25-2.83) and 2.47 points in ERRALS (95% CI 1.07-3.86). However, the linear and quadratic interactions together increased the marginal R

conclusionsThe pre-diagnostic ALSFRS-R slope identifies meaningful average differences in subsequent decline between patient groups but provides limited information for predicting individual trajectories.