Physiologic deficits in the orofacial system underlying dysarthria in amyotrophic lateral sclerosis

The purpose of this study was to delineate some of the physiological deficits in the orofacial musculature of patients with dysarthria associated with amyotrophic lateral sclerosis (ALS) and to relate the physiologic deficits to perceived severity of dysarthria. Strain gauge force transducers placed on the lower lip, jaw, and tongue tip were used to measure maximum strength and maximum rate of repeated contractions. Diadochokinetic rates for repeated /pe/ and and /te/ were also determined. Fourteen ALS patients and 15 normal subjects were tested. It was found that the ALS patients with dysarthria were impaired in all tasks compared to the normal subjects, and that some measures revealed impairment even in those ALS patients who were not yet dysarthric. Bulbar ALS patients were generally more severely affected than the corticobulbar or spinal ALS patients, and the tongue was generally the most affected structure in all ALS groups. Perceived severity of dysarthria was more highly correlated with the measures of repeated contraction rate than with the measures of strength, suggesting that more severe dysarthria may be largely due to slower movement of the orofacial structures until substantial muscle strength has been lost.