Background: Myotonic dystrophy type 1 (DM1) is a slowly progressive multi-systemic disease with an autosomal-dominant inheritance caused by a mutation on chromosome 19 (19q13.3).
Aims: To explore speech characteristics in a group of individuals with the congenital and childhood-onset forms of DM1 in terms of intelligibility, speech-sound production, nasality and compensatory articulation. A further aim was to analyse whether speech characteristics were correlated to subforms of DM1 and if speech outcome could be related to muscle strength.
Methods & procedures: Fifty native Swedish speakers (7-29 years old) with the congenital and childhood-onset forms of DM1 and 13 healthy controls participated in the study. The intelligibility of spontaneous speech, speech-sound production - single-word and sentence repetition - including percentage consonants correct (PCC) and compensatory articulation, were evaluated by speech-language pathologists from video recordings. A nasometer and lip-force meter were used for objective evaluations of nasality and orofacial strength.
Outcomes & results: In severe (n = 9) and mild congenital DM1 (n = 13), all participants had impaired intelligibility to some degree, while this applied to 79% of those with childhood DM1 (n = 28). PCC for bilabials were 53.9% in severe congenital DM1, 57.4% in mild congenital DM1 and 85.3% in childhood DM1; the corresponding results for dentals were 69.3%, 59.2% and 87.3%. Bilabials were most often compensated for with interdental or labiodental articulation. Dentals were substituted with interdental articulation. Velars were seldom affected. The mean nasalance score was high in the study group compared with controls and with normative data and the majority had weak lips. Maximum lip force, as well as the mean nasalance score, correlated significantly with the intelligibility score.
Conclusions & implications: The deviant production of bilabial consonants, interdental articulation and hypernasal speech are characteristic features of dysarthria in congenital and childhood DM1. Dysarthria is more frequent and more severe in congenital DM1 compared with childhood DM1. Most individuals with congenital DM1 and childhood-onset DM1 will need speech therapy from a young age. For some children with incomprehensible speech or severe neurodevelopmental disorders, alternative and augmentative ways of communication will be part of the treatment.
Keywords: dysarthria; hypernasality; intelligibility; muscle weakness; myotonic dystrophy; speech.
© 2018 Royal College of Speech and Language Therapists.