Dysphagia is one of the most critical problems in patients with progressive neuromuscular diseases. However, clinically useful and practical scales to evaluate dysphagia are limited. Therefore, the aim of this study was to develop such a scale. An 8-stage Neuromuscular Disease Swallowing Status Scale (NdSSS) was developed and tested for its inter- and intrarater reliabilities, concurrent validity, and responsiveness. The NdSSS was used to evaluate 134 patients with Duchenne muscular dystrophy (DMD) and 84 patients with amyotrophic lateral sclerosis (ALS). Inter- and intrarater reliabilities were examined with weighted kappa statistics. Concurrent validity was assessed by correlating the NdSSS with the existing scales [Functional Oral Intake Scale (FOIS), Functional Intake LEVEL Scales (FILS), and ALS Functional Rating Scale-Revised Swallow (ALSFRS-R Sw)], using Spearman's correlation coefficients. Responsiveness was determined with the standardized response mean (SRM). For inter- and intrarater reliabilities, the weighted kappas were 0.95 and 1.00, respectively, for DMD; and 0.98 and 0.98, respectively, for ALS. The NdSSS showed strong correlations with the FOIS (rs = 0.87 for DMD, rs = 0.93 for ALS, p < 0.001), FILS (rs = 0.89 for DMD, rs = 0.92 for ALS, p < 0.001), and ALSFRS-R SW (rs = 0.93, p < 0.001). SRMs were 0.65 for DMD and 1.21 for ALS. The SRM was higher in DMD patients for the NdSSS than for the other scales, while it was similar in ALS patients and the other scales. Our originally developed NdSSS demonstrated sufficient reliability, validity, and responsiveness in patients with DMD and ALS. It is also useful in evaluating dysphagia in patients with progressive neuromuscular diseases.
Keywords: Amyotrophic lateral sclerosis; Instrument; Muscular dystrophy; Psychometric properties; Swallowing disorders.