What does the ALSFRS-R really measure? A longitudinal and survival analysis of functional dimension subscores in amyotrophic lateral sclerosis

Abstract

Introduction: ALSFRS-R is the most widely used functional rating system in ALS patients. However, heterogeneity in ALSFRS-R progression renders analysis challenging. We have explored the characteristics of total ALSFRS-R, and ALSFRS-R sub-scores in longitudinal and survival models, to determine whether sub-score analysis enhances the precision of the instrument.

Methods: All cases with ALSFRS-R scores on the Irish ALS register were included. ALSFRS-R sub-scores were defined for bulbar, motor and respiratory domains. Longitudinal models were used to visualise fitted total and sub-score ALSFRS-R progression. In addition the prognostic value of convenience and computed ALSFRS-R slope and sub-score slopes were compared.

Results: 407 incident cases were identified with a complete ALSFRS-R measure. 233 (57%) patients were male, and 125 (31%) had bulbar-onset disease. ALSFRS-R bulbar and motor sub-score slopes provided better fit in prognostic models when combined over total ALSFRS-R slope. Longitudinal analysis revealed that the ALSFRS-R motor sub-score deteriorated earlier in spinal-onset disease over bulbar, while in bulbar-onset disease the ALSFRS-R bulbar sub-score deteriorated earlier, and faster than in spinal onset disease.

Discussion: Our analysis builds on previous knowledge of ALSFRS-R sub-scores. Decline in ALSFRS-R motor sub-scores in patients with spinal onset disease, and decline in ALSFRS-R bulbar sub-scores in patients with bulbar onset disease, may pre-date reported disease onset dates. Respiratory sub-scores were not prognostically informative after adjustment for bulbar and motor sub-scores. These results provide robust evidence that the ALSFRS-R should not be reported as a single combined score, but rather as domain specific sub-scores.