Relative effects of forced vital capacity and ALSFRS-R on survival in ALS

Amyotrophic lateral sclerosis (ALS) is a degenerative neuromuscular disease with marked clinical heterogeneity. This heterogeneity can be partly captured by clinical measures, such as the forced vital capacity (FVC) and ALS Functional Rating Scale-Revised (ALSFRS-R). We aimed to further characterize the performance of these clinical measures, including their independence and additivity, in predicting mortality.

We leveraged the Pooled Resource Open-Access ALS Clinical Trials (PRO-ACT ALS) database, which includes data from 23 clinical trials (n = 2050). The primary exposures were baseline FVC and ALSFRS-R. The primary outcome was 1-y mortality. We performed correlation analyses, survival analyses and assessed classification performance using receiver operator characteristic (ROC) curves.

FVC and ALSFRS-R were weakly correlated (r = 0.31, p < .001). A 1-SD increase in FVC (hazard ratio [HR]: 0.66; 95% confidence interval [CI]: 0.59-0.74) and ALSFRS-R (HR: 0.75; 95% CI: 0.68-0.82) were associated with reduced risk of 1-y mortality. ROC analyses showed optimal predictive cutoffs at 80% for FVC (area under the curve [AUC]: 0.69) and 38 for ALSFRS-R (AUC: 0.67). After stratifying patients based on these cutoffs, we found a marked reduction (HR: 0.25; 95% CI: 0.19-0.33) in incident mortality for patients in the high FVC and high ALSFRS-R group relative to the low FVC and low ALSFRS-R group.

ALSFRS-R and FVC are comparable predictors of survival that are only weakly correlated. When considered together, they synergistically predict survival. As such, consideration of both measures should be a routine part of prognostication in care of patients with ALS.