Abstract
PurposeThe effects of neuromodulation are virtually unexplored in adductor laryngeal dystonia (AdLD), a disorder characterized by involuntary contraction of intrinsic laryngeal muscles. Recent findings indicated that intracortical inhibition is reduced in people with AdLD. Low-frequency repetitive transcranial magnetic stimulation (rTMS) induces prolonged intracortical inhibition, but the effects in AdLD are unexplored. This pilot and feasibility study aimed to examine the safety, feasibility, and effects of a single session 1 Hz rTMS over the laryngeal motor cortex (LMC) in people with AdLD and healthy individuals.MethodsThe stimulation location was individualized and determined through TMS-evoked responses in the thyroarytenoid muscles using fine-wire electrodes. 1200 pulses of 1 Hz rTMS were delivered to the left LMC in two groups: Control (n = 6) and AdLD (n = 7). Tolerance, adverse effects, intracortical inhibition, and voice recordings were collected immediately before and after rTMS. Voice quality was assessed with acoustic-based and auditory-perceptual measures.ResultsAll participants tolerated the procedures, with no unexpected adverse events or worsening of symptoms. No significant effects on intracortical inhibition were observed. In the AdLD group, there was a large-effect size after rTMS in vocal perturbation measures and a small-effect size in decreased phonatory breaks.ConclusionsOne rTMS session over the LMC is safe and feasible, and demonstrated trends of beneficial effects on voice quality and phonatory function in AdLD. These preliminary findings support further investigation to assess clinical benefits in a future randomized sham-controlled trial.ClinicalTrials.govNCT02957942, registered on November 8, 2016.
Highlights
Adductor laryngeal dystonia (AdLD) is the most common form of laryngeal dystonia, a rare disorder characterized by excessive contraction of intrinsic muscles in the larynx
Neck pain was reported by some participants (n = 5) which was likely related to discomfort associated with head positioning during transcranial magnetic stimulation (TMS)/repetitive transcranial magnetic stimulation (rTMS) procedures
These dissimilarities were due to the higher percentage of females with AdLD diagnosis and the challenge of recruiting healthy older individuals willing to undergo the experimental procedures involved in the study. This potential confound was minimized by adjusting the repeated measures analysis of variance (RMANOVA) for age. This pilot study explored the effects of rTMS targeting the laryngeal motor cortex (LMC) and the affected musculature in AdLD
Summary
Adductor laryngeal dystonia (AdLD) ( referred to as spasmodic dysphonia) is the most common form of laryngeal dystonia, a rare disorder characterized by excessive contraction of intrinsic muscles in the larynx. People affected by AdLD often have a strained voice quality and experience phonatory breaks during speech due to intermittent hyper-adduction of the vocal folds (Ludlow et al 2008) These symptoms impair effective communication, and can have a negative impact on many aspects of patients’ lives, such as occupation and social participation. Benefits of botulinum toxin injections are only short term and not universally effective (Ludlow et al 2008) Other treatment options such as voice and speech therapy may be less effective than botulinum toxin injections, and selective laryngeal adductor denervation–reinnervation surgery may be less effective and present greater risk to patients (Ludlow et al 2008, 2018; Simonyan et al 2021). Current priorities indicate the pressing need for novel interventions in laryngeal dystonia (Simonyan et al 2021)
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