Abstract
Objective: Understanding clinical variants of motor neuron diseases such as amyotrophic lateral sclerosis (ALS) is critical for discovering disease mechanisms and across-patient differences in therapeutic response. The current work describes two clinical subgroups of patients with ALS that, despite similar levels of bulbar motor involvement, have disparate clinical and functional speech presentations.Methods: Participants included 47 healthy control speakers and 126 speakers with ALS. Participants with ALS were stratified into three clinical subgroups (i.e., bulbar asymptomatic, bulbar symptomatic high speech function, and bulbar symptomatic low speech function) based on clinical metrics of bulbar motor impairment. Acoustic and lip kinematic analytics were derived from each participant's recordings of reading samples and a rapid syllable repetition task. Group differences were reported on clinical scales of ALS and bulbar motor severity and on multiple speech measures.Results: The high and low speech-function subgroups were found to be similar on many of the dependent measures explored. However, these two groups were differentiated on the basis of an acoustic measure used as a proxy for tongue movement.Conclusion: This study supports the hypothesis that high and low speech-function subgroups do not differ solely in overall severity, but rather, constitute two distinct bulbar motor phenotypes. The findings suggest that the low speech-function group exhibited more global involvement of the bulbar muscles than the high speech-function group that had relatively intact lingual function. This work has implications for clinical measures used to grade bulbar motor involvement, suggesting that a single bulbar measure is inadequate for capturing differences among phenotypes.
Highlights
Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease resulting in the progressive loss of limb, trunk, and head and neck motor function
The findings support the existence of distinct phenotypes that, despite presenting with similar levels of bulbar motor involvement, exhibited disparate clinical and functional speech presentations
Within the bulbar symptomatic group, we identified a potential stratification into two subgroups based on highly disparate clinical presentations of functional speech: a
Summary
Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease resulting in the progressive loss of limb, trunk, and head and neck (bulbar) motor function. The disease is characterized by significant across-patient heterogeneity in onset region, and pattern and rate of progression [1, 2]. Understanding this heterogeneity in bulbar presentation is critical for improved understanding of disease symptomatology, as well as causes and implications of variability in expression, pathophysiology, and therapeutic response [3,4,5,6]. Despite its complex and varied clinical manifestation [7], bulbar motor involvement in ALS has largely been considered a single variant, primarily graded on the severity of speech and swallowing symptoms [8]. The findings support the existence of distinct phenotypes that, despite presenting with similar levels of bulbar motor involvement, exhibited disparate clinical and functional speech presentations
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