Multidimensional Measurements of Dysarthria in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is a heterogeneous neuromuscular disorder characterized by progressive muscle weakness and myotonia. Dysarthria is a known symptom of DM1, but literature is lacking about the patient's own perception in relationship to dysarthria characteristics and severity.

The aim of the study was to describe the acoustic speech characteristics of dysarthria in patients with DM1, examine the perceptually determined dysarthria severity through speech and language therapy assessment, gather subjective evaluations of speech and intelligibility from patients and relatives and examine the relationship between these outcomes.

The speech of 22 adult patients with DM1 (nine females) was acoustically assessed during spontaneous speech, reading, and maximum performance tasks and analysed using the Praat-software. Dysarthria severity was rated on a severity scale from 0 (no dysarthria) - 5 (very severe dysarthria/anarthria). Patients and relatives rated the speech with a short questionnaire and a visual analogue scale (VAS).

Acoustic analysis showed a deviant speech rate (SR), articulation rate (AR), maximum phonation volume (MPV), and fundamental frequency range compared to normative values. Perceptually, the dysarthria severity scores varied between 1 (minimal dysarthria) and 4 (severe dysarthria). In more severe dysarthria, SR, AR, and MPV decreased. Patients were sufficiently satisfied about their speech, with no relationship to dysarthria severity. However, the scores of relatives decreased when perceptual dysarthria severity increased.

As dysarthria severity increased, speech quality and intelligibility declined, particularly when assessed by speech therapists and relatives. Patients with DM1 generally reported minimal conversational restrictions due to dysarthria. Multidimensional measurements may improve the understanding of speech impairment in DM1. Self-awareness should be a topic in speech therapy interventions.

What is already known on this subject Dysarthria is a common symptom in myotonic dystrophy type 1 (DM1). Research has focused on articulatory accuracy and SR. Cognitive decline in patients with DM1 is known to reduce illness insight in approximately half of the cases. However, its impact on self-awareness of dysarthria, and how this compares to perceptions of relatives and speech therapists, had not been investigated prior to this study. The combination of acoustic and perceptual speech measures with patients' own perspectives provides new knowledge of speech monitoring in DM1. What this study adds to existing knowledge This is the first study to investigate speech in patients with DM1 using both acoustic and perceptual analyses, while simultaneously examining the relationship with patients' self-awareness of their speech impairments. The results of this study show a relationship between increasing perceptual dysarthria severity and decreasing acoustic speech performance. Patients often rate their own speech more optimistically than relatives and speech therapists, which suggests a possible role of neuropsychological impairment in reduced self-awareness of speech deficits in DM1, warranting further research. What are the potential or actual clinical implications of this study? The integration of acoustic and perceptual speech assessment allows an objective and accurate diagnosis of dysarthria in DM1. Speech therapy should focus on improving speech clarity and intelligibility by developing exercises for articulatory precision and respiratory control. The discrepancy between how patients perceive their own speech and the opinion of clinicians and relatives suggests that speech therapists may need to focus on raising awareness of the dysarthria and actively involve relatives in the therapeutic process.