Longitudinal Objective Assessment of Speech in Multiple Sclerosis

Background Remote objective tests may supplement in-clinic examination to better inform treatment decisions. Previous cross-sectional studies presented objective speech metrics as potential markers of Multiple Sclerosis (MS) disease progression. Objective To examine the short-term stability and long-term sensitivity of speech metrics to MS progression. Methods We prospectively recorded speech from people with MS at baseline, six, twelve weeks, and at ten months or longer after baseline (1y+). Only people with a definite diagnosis of MS and without other potential causes of dysarthria were included. Speech tasks comprehended 1) a sustained vowel /a/, 2) saying the days of the week, 3) repeating the non-word pa-ta-ka multiple times as fast as possible, 4) reading the Grandfather Passage, and 5) telling a personal story. We selected speech metrics of interest according to their association with MS presence, correlation with general disability, and short-term metric stability in the absence of disease progression. Selected speech metrics were analysed for short- versus long-term changes in the whole MS cohort and in the clinically stable versus progression subgroups at 1y+. Results Sixty-nine people with MS participated (76.8% female, age mean 47.5±11.1 SD, EDSS median 3.5, interquartile range 3.5). Twenty-six unique speech metrics satisfied the suitability criteria. On average, reading rate improved 3.5% for all people with MS and 6.5% for slow readers with MS from baseline to the six-week, driven by a reduction in pauses. At 1y+, participants showed a 3.1% average reduction in vocalization time during the reading task, which was similar in the progression (n=29) and non-progression (n=40) groups and thus unrelated to disease progression. Both findings are in the opposite direction of what would be generally expected for deterioration in speech performance and might be attributable to familiarity and training effects. Other speech metrics showed either negligible change or a similar variability between short-term and long-term differences. Conclusion Most individual long-term changes were small and within short-term variability intervals, irrespective of clinical disease progression. Familiarity and practice effects might have blunted the measurement of change. The present lack of longitudinal sensitivity of speech in MS contradicts previous cross-sectional findings and requires further investigation.