The impact of diagnostic criteria on the detection of nocturnal hypoventilation in adult amyotrophic lateral sclerosis patients

Background Nocturnal hypoventilation (NH) is an early manifestation of respiratory muscle weakness in amyotrophic lateral sclerosis (ALS) and plays a key role in determining the optimal timing for non-invasive ventilation (NIV). However, several diagnostic definitions of NH have been proposed, and their impact on NH prevalence remains unclear. Methods In this cross-sectional study, 56 non-ventilated ALS patients underwent home-based overnight monitoring with transcutaneous carbon dioxide (TcCO 2 ) and pulse oximetry. NH prevalence was assessed using seven definitions derived from daytime arterial blood gases, nocturnal oximetry, and TcCO 2 parameters. Agreement between definitions was evaluated using Cohen’s and Light’s kappa coefficients. Results NH prevalence varied widely depending on the definition used, ranging from approximately 5% with daytime arterial criteria to 36.7% using peak TcCO 2 ≥49 mmHg. Overall concordance among definitions was low (Light’s κ=0.27), indicating that current NH definitions are not interchangeable. Conclusions Currently used definitions of NH in ALS show substantial heterogeneity and identify different patient subsets. These findings highlight the need for ALS-specific consensus definitions of NH.