Sensory trick efficacy in cervical dystonia is linked to processing of neck proprioception

Abstract

Background: Muscle vibration activates muscle spindles and when applied over posterior neck muscles during stance modulates global body orientation. This is characterised by a tonic forward sway response that is reportedly diminished or absent in patients with idiopathic cervical dystonia. Objective: To investigating the impact of the sensory trick on vibration-induced postural responses. Methods: 20 patients with idiopathic cervical dystonia and a sensory trick, 15 patients without a trick, and 16 healthy controls were recruited. Neck muscle vibration was applied bilaterally over the upper trapezius under three different conditions: 1) Quiet standing; 2) standing while performing the trick (or trick-like movement in non-responders); 3) standing while elevating the flexed arm without touching any part of the body. Centre of pressure position and wholebody orientation in the sagittal plane were analysed. Results: Patients with a sensory trick responded similarly to healthy controls: neck muscle vibration led to an initial forward sway of the body that slowly increased during the prolonged vibration for all three conditions. This response was mainly mediated by ankle flexion. In patients without a trick, the initial sagittal sway was significantly reduced in all three conditions and the later slow increase was absent. Performance of the trick did not have an effect on any aspect of the response in either cervical dystonia group. Conclusions: The whole-body response to neck vibration in cervical dystonia differs depending on the effectiveness of the sensory trick to alleviate the dystonic neck posture. Variable pathophysiology of proprioceptive processing may be the common factor.

Neurobiological mechanisms associated with antipsychotic drug-induced dystonia

“…Perhaps consideration of the pathophysiology of focal dystonia such as task-specific focal dystonia (Altenmüller and Müller, 2013; Goldman, 2015; Hallett, 2011) and cervical dystonia (Brugger et al, 2019; Popa et al, 2018) can help to understand the mechanism of antipsychotic drug-induced dystonia. Both types of focal dystonia may also show transient improvement when applying so-called ‘sensory tricks’ (Mailankody and Pal, 2017), both types may respond to chemodenervation with intramuscular botulinum toxin injection in relevant muscles (Kaňovský and Rosales, 2011; Rosales and Dressler, 2010) and both are accompanied by altered proprioceptive functioning (Mailankody and Pal, 2017; Nevrlý et al, 2018).…”

“…This indicates that aberrant functioning within somatomotor circuits may be a common principal physiopathological mechanism. In some types of dystonia, dysfunction of the cerebral cortex (Altenmüller and Müller, 2013; Brugger et al, 2019; Hallett, 2011) or cerebellum (Popa et al, 2018; Prudente et al, 2014) may be most important, but in antipsychotic drug-induced dystonia this more likely to represent a malfunctioning of converging CSTC circuits within the basal ganglia. This is supported by the close relationship of drug-induced dystonia with a blockade of dopamine D2 receptors and the increased vulnerability to acute drug-induced dystonia after exposition to cocaine.…”

Sensorimotor Control in Dystonia

“…The impairment was also present when muscle vibration produced the illusion of movement alone, and was generalized to other muscle groups [20,21]. In cervical dystonia (CD), vibration of neck muscles produced smaller changes in posture and sway than in healthy controls [22], but postural responses could be rescued by the application of a sensory trick, which alleviates dystonic symptoms in some patients [23]. Other evidence suggests that the abnormal tonic vibration reflex is rescued by muscle fatigue in patients with CD [24] and may be a promising endophenotypic marker for idiopathic focal dystonia due to its heritability [25].…”

Oral splint ameliorates tic symptoms in patients with tourette syndrome

“…Interestingly, the effectiveness of the sensory trick in cervical dystonia is associated with neural processing of proprioception. 5 The oral splint would modulate proprioceptive signals from jaw-closing muscle spindles, which are conveyed to the insular cortex 6 ; the abnormal insular hyperactivity has also been reported in TS patients. 7 Further studies are needed to reconfirm the therapeutic benefit of the oral splint and elucidate its underlying mechanism.…”

“…The oral splint might exert a placebo effect, but should serve as a sensory trick that ameliorates symptoms in tics as well as in dystonia. Interestingly, the effectiveness of the sensory trick in cervical dystonia is associated with neural processing of proprioception . The oral splint would modulate proprioceptive signals from jaw‐closing muscle spindles, which are conveyed to the insular cortex; the abnormal insular hyperactivity has also been reported in TS patients .…”