Defining clinically meaningful thresholds for forced vital capacity in patients with neuromuscular disorders: Lessons learned from the COMET study in Pompe disease

Background Respiratory impairment in neuromuscular disorders (NMDs) is generally assessed using forced vital capacity (FVC). Any improvement in FVC trajectory will delay ventilatory support; however, the change required for patients to perceive a noticeable clinical benefit, the clinically meaningful threshold (CMT), has not been defined in NMDs.Objective To derive the within-person and between-group CMTs for FVC (% predicted) in patients with late-onset Pompe disease (LOPD).Methods This analysis leverages data from the Phase 3 COMET trial (NCT02782741, registered 25 May 2016), which assessed the efficacy of avalglucosidase alfa (AVA) versus alglucosidase alfa (ALG) on upright FVC (% predicted) in LOPD. Anchor- and distribution-based methods were used to estimate the within-person and between-group CMTs for FVC at Weeks 49 and 97.Results COMET enrolled 99 participants aged >= 18 years (52% male; mean age 48.0 years). The within-person CMT for absolute change in FVC expressed as % predicted was estimated as 3.0% [95% confidence interval (CI) 2.3, 3.8]. The proportion of patients with a meaningful increase in FVC was higher in the AVA versus ALG group across the CI of the estimated CMT (odds ratios: 2.3-2.6; nominal p-values: 0.026-0.058). The between-group CMT, needed to evaluate differences between treatment groups, was estimated as 2.1% predicted [95% CI 1.1, 3.1].Conclusions We identified a narrow range of within-person and between-group CMTs for upright FVC (% predicted) in LOPD. Post hoc application of these thresholds to COMET showed that a greater proportion of patients in the AVA group had clinically meaningful improvement in FVC versus ALG. These findings may aid in interpretation of data from studies in other NMDs.