Impaired Limb Proprioception in Adults With Spasmodic Dysphonia

Abstract

Objectives Focal dystonia of the head, neck are associated with a loss of kinaesthetic acuity at muscles distant from the dystonic sites. That is, while the motor deficits in focal dystonia are confined, the associated somatosensory deficits are generalized. This is the first systematic study to examine, if patients diagnosed with spasmodic dystonia (SD) show somatosensory impairments similar in scope to other forms of focal dystonia. Methods Proprioceptive acuity (ability to discriminate between two stimuli) for forearm position and motion sense was assessed in 14 spasmodic dystonia subjects and 28 age-matched controls using a passive motion apparatus. Psychophysical thresholds, uncertainty area and a proprioceptive acuity index were computed based on the subjects’ verbal responses. Results The main findings are: First, the SD group showed significantly elevated thresholds and uncertainty areas for forearm position sense when compared to the control group. Second, 9 out of 14 dystonia subjects (64%) exhibited an acuity index for position sense above the control group maximum. Three SD subjects had a motion sense acuity index above the control group maximum. Conclusion The results indicate that impaired limb proprioception is a common feature of SD. Like other forms of focal dystonia, spasmodic dystonia does affect the somatosensation of non-dystonic muscle systems. That is, SD is associated with a generalized somatosensory deficit.

Laryngeal vibration as a non-invasive neuromodulation therapy for spasmodic dysphonia

“…Recent work from our group demonstrated upper limb proprioceptive deficits in SD 12 . Moreover, studies on the effects of sensory stimulation of the larynx have indicated a reduced inhibition of laryngeal muscle responses to sensory stimulation, i.e., a reduced suppression of motor responses to laryngeal sensory stimulation 5 .…”

“…Abnormal kinaesthetic function has been reported in non-dystonic limbs and muscle systems in SD 12 and other forms of focal dystonia such as blepharospasm and cervical dystonia 10 . This implies that a more generalized somatosensory deficit underlies or is associated with the focal motor dysfunction in dystonia.…”

“…The underlying neural mechanism of SD is not entirely understood, but it is known to involve structural and functional alterations in the basal ganglia–thalamo-cortical circuitry, the brainstem, and the cerebellum 4–8 . Several forms of focal dystonia, including cervical dystonia (CD), blepharospasm, and spasmodic dysphonia present with somatosensory system abnormalities even in non-dystonic muscles 9–12 . This suggests that while the motor symptoms of dystonia are focal, the corresponding somatosensory impairments are general.…”

Atypical somatosensory-motor cortical response during vowel vocalization in spasmodic dysphonia

“…Previous work by our team had shown a generalized proprioceptive deficit in musician's dystonia (Konczak et al, 2013) and in SD (Konczak et al, 2015). This raises the question if one can identify atypical patterns of somatosensory activation and/or abnormal interaction between somatosensory and motor cortical areas that underlie the observed proprioceptive and motor dysfunction in spasmodic dysphonia.…”

Actual and Illusory Perception in Parkinson's Disease and Dystonia: A Narrative Review

“…Furthermore, the perception of arm movement during tonic vibration reflex or during illusory movements induced by vibration in an immobilized arm has been found to be abnormal ( 26 , 27 ) (Table 1 ). Interestingly, proprioceptive acuity has been found to be decreased even in non-dystonic muscles, e.g., in the limb muscles of patients affected by spasmodic dystonia ( 33 ). These sensory abnormalities may impair the process of sensorimotor integration in dystonia.…”