An investigation of factors associated with speech intelligibility in patients with amyotrophic lateral sclerosis: Integrating acoustic and lingual motor measures.

Speech intelligibility in amyotrophic lateral sclerosis (ALS) progressively declines, but contributing clinical factors may vary according to disease presentation and extent of bulbar involvement. This study examined factors associated with intelligibility in three ALS groups: spinal-onset, spinal-onset with bulbar involvement (spinal + bulbar), and bulbar-onset. Speech intelligibility (visual analogue scale), hypernasality, maximum tongue pressure, respiratory function (%VC and FEV1/FVC), and second formant (F2) transition measures (transition duration and excursion) were evaluated. Exploratory two- and three-dimensional visualisations were used to examine interrelationships among variables, and regression analyses were conducted in groups with sufficient sample size. In spinal-onset ALS, only hypernasality was associated with intelligibility. In bulbar-onset ALS, both tongue pressure and hypernasality were significantly associated with intelligibility, while preserved F2 excursion showed an additional trend towards better intelligibility. In the spinal + bulbar group, descriptive findings suggested that reduced tongue pressure and increased hypernasality were associated with lower intelligibility. These findings suggest that speech intelligibility in ALS is influenced by different combinations of bulbar-related impairments depending on clinical presentation and extent of bulbar involvement. In particular, tongue strength, velopharyngeal function, and residual tongue mobility may be relevant to intelligibility outcomes with bulbar involvement. Combined evaluation of these measures may help inform individualised clinical assessment and management.