To assess the reliability of slow vital capacity (SVC) measured at home (hSVC) compared to SVC measured in the clinic (cSVC) in a phase 2 trial evaluating reldesemtiv in amyotrophic lateral sclerosis (ALS).

SVC is used to evaluate ventilatory function in ALS patients. However, frequent in-clinic visits can prove challenging. A portable spirometer allows SVC to be measured at home, thereby reducing the burden of clinical trial participation. In an ongoing Phase 2 clinical study, FORTITUDE-ALS, we evaluate SVC measured both at home and in the clinic

In FORTITUDE-ALS, patients are trained to use portable spirometers to measure hSVC weekly in addition to performing cSVC at specified time points. Results of cSVC are paired with hSVC conducted within a 7-day window. The Pearson correlation coefficient and differences between the two SVCs were calculated. The difference between the two measures was analyzed using a paired t-test.

As of October 15, 2018, 238/322 (73.9%) dosed patients in FORTITUDE-ALS performed hSVC measurements that could be paired with clinic values; the Pearson correlation coefficient was 0.94 (p<0.0001). The mean difference between results of hSVC and cSVC is 0.153 liters (standard deviation, 0.3607; p<0.0001).

Home SVC measurements by ALS patients appear highly correlated to, but significantly different from, those performed in the clinic.  Home measurements could permit more frequent monitoring of ALS ventilatory function allowing for more timely clinical decisions, including when to initiate non-invasive ventilation. However, the significant discrepancy between hSVC and cSVC may raise concerns regarding the advisability of decreasing the frequency of in-clinic trial visits by substituting hSVC for cSVC. More comprehensive evaluation of the utility of this outcome measure and results from a site survey regarding potential obstacles to compliance will be presented after the study is completed.