Validation of the Dynamic Imaging Grade of Swallowing Toxicity for Amyotrophic Lateral Sclerosis

Introduction: Although dysphagia is prevalent in persons with amyotrophic lateral sclerosis (pALS) and is associated with morbidity and mortality, no validated outcomes currently exist for the gold standard videofluoroscopy (VF) exam. We therefore sought to psychometrically validate the Dynamic Imaging Grade of Swallowing Toxicity (DIGEST) scale in pALS. Methods: One hundred pALS attended a research evaluation and underwent a standardized VF and validated clinical outcomes of oral intake (FOIS), perceived swallowing impairment (EAT-10), and ALS disease progression (ALSFRS-Revised). Duplicate, independent, and blinded VF ratings were completed using the DIGEST and MBSImP scales. Weighted kappa, ANOVAs (Tukey's HSD, Welch's correction), and Chi-square analyses were performed to determine intra- and inter-rater reliability, criterion validity, and construct validity of the DIGEST scale for use in pALS. Results: The mean age was 64.4(SD = 10.4), 50% were male, and the average ALS duration was 28.2 months (SD = 22.2). Excellent intra-rater (kappa = 0.92-1.0) and inter-rater (kappa = 0.94) reliability were noted for DIGEST ratings. DIGEST grades significantly discriminated pharyngeal pathophysiology (MBSImP, F(3,96) = 24.7, p < 0.0001), perceived dysphagia (EAT-10, F(3,40) = 20.8, p < 0.0001), oral intake (FOIS, X-2:25.4, df = 3, p < 0.0001), ALS bulbar disease progression (ALSFRS-bulbar, F(3,93) = 20.8, p < 0.0001) with main effects noted for all analyses. Post hoc pairwise comparisons noted differences across all DIGEST grades with the exception of DIGEST 2 versus 3 (moderate vs. severe dysphagia), p > 0.05. Conclusions: These data confirm that the DIGEST scale is a reliable and valid VF outcome for use in pALS to distinguish normal versus impaired swallowing and mild versus moderate or severe dysphagia for use in clinical practice and as a clinical trial endpoint marker.