The effect of fatigue on abnormal vibration induced illusion of movement in idiopathic focal dystonia

Abstract

Background: Perception of vibration induced illusionary movement (VIIM) is subnormal in dystonic patients, suggesting abnormal sensory-motor processing in patients with idiopathic focal dystonia. Objective: To examine the effects of fatigue on VIIM in patients with idiopathic torticollis. Methods: An illusionary sensation of arm extension was evoked by an 80 Hz transcutaneous vibratory stimulus applied to the biceps brachii tendon while the arm was restrained. Blindfolded patients attempted to copy the perceived movement of the vibrated arm with the opposite (tracking) arm and the change in elbow angle of the tracking arm was quantified over 45 seconds. The tasks were repeated following volitional fatigue of the vibrated arm. Results: The subnormal perception of VIIM perceived by patients with torticollis, occurring bilaterally and remote from the location of dystonic symptoms, was corrected by fatigue of the vibrated arm compared with prefatigue values (mean (SEM): 19.04°(1.76)°v 24.25°(2.41°); p = 0.01, paired t test). Conclusions: While a combination of central or peripheral factors may be involved in the correction of abnormal perception of the vibration induced illusion of movement in dystonia, subnormal elasticity of muscle spindles could be implicated in the impaired perception of vibration induced illusionary movement and may predispose an individual towards developing idiopathic focal dystonia.

Sensory functions in dystonia: Insights from behavioral studies

“…In this task, subjects are asked to reproduce the direction and amplitude of the movement they perceive in the vibrated arm by actively moving the tracking arm. [39][40][41][42] A more recent method that assesses the temporal aspects of proprioceptive discrimination, delivers pairs of electrical stimuli to the motor point of hand or forelimb muscles. 47,53 These stimuli produce muscle contraction and passive joint movement, and subjects have to indicate the shortest interval between two electrical stimuli at which they perceive two separate movements.…”

“…[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]47 This impairment may play an important role in the pathophysiology of dystonia. [48][49][50] …”

“…[19][20][21][22][23] Recent behavioral studies have shown that these sensory functions are compromised in patients with several forms of primary dystonia. Changes have been found in: (1) temporal discrimination and integration of sensory signals [24][25][26][27][28][29][30][31][32][33] ; (2) spatial discrimination of tactile stimuli 28,[34][35][36][37][38] ; (3) vibration-induced illusion of movements [39][40][41][42] ; and (4) movement representation and learning. [43][44][45][46] In this review, we focus on the possible role of abnormal sensory processing in the pathophysiology of primary dystonia, highlighting potential implications for innovative therapeutic strategies to aid functional recovery.…”

Animal models of focal dystonia

“…43 Similarly, the perception of vibration induced illusion of movement is subnormal in patients with spasmodic torticollis. 46 One striking aspect of the sensory changes that occur with cervical dystonia is that approximately 70% of the patients have a sensory trick that alleviates the dystonic posture. 31 For example, touching the cheek reduces agonist EMG activity in the dystonic muscle by 48%.…”

Dystonia Arising from Occupations: The Clinical Phenomenology and Therapy

“…On the other hand the vibration induced illusion of movement model suggest a mechanism whereby motor subroutines become corrupted when movements are over-learned in the fatigued state (13)(14)(15). In idiopathic focal dystonia, the muscle spindles become stiff and their elastic properties vary as they are stretched or what is termed as "spindle thixotrophy" (16)(17).…”