Examining the Speech Intelligibility of Individuals With Oromandibular Dystonia Receiving Botulinum Toxin: A Series of Cases

Oromandibular dystonia is a focal dystonia affecting the facial, lingual, and labial musculature. Oromandibular dystonia can result in a hyperkinetic dysarthria with associated reductions in speech intelligibility. Botulinum toxin A injections are the gold standard in the therapeutic management of oromandibular dystonia. Unfortunately, there is a sparse empirical literature that has examined changes to speech intelligibility in individuals receiving botulinum toxin A therapy. In this preliminary study, we measured the speech intelligibility of 10 individuals with oromandibular dystonia at two time points over the course of a therapeutic botulinum toxin A injection cycle. Intelligibility was assessed using the Sentence Intelligibility Test and a conversational speech task. Four listeners rated sentence intelligibility and conversational intelligibility via visual analogue scaling. Changes to speech intelligibility over the course of the botulinum toxin A treatment cycle were analyzed using a series of cases. The speech intelligibility of one individual with lingual oromandibular dystonia demonstrated significant increases to speech intelligibility over the course of the treatment cycle. The remaining nine participants demonstrated relative stability in speech intelligibility scores over the course of the treatment cycle. It appears that for jaw opening, jaw closing, and mixed presentations of oromandibular dystonia, botulinum toxin A injections did not significantly reduce or improve speech intelligibility. Our preliminary results provide a rationale for examining speech intelligibility and the response to botulinum toxin A based on the type and location of oromandibular dystonia in larger scale study.