Abnormal vibration‐induced illusion of movement in idiopathic focal dystonia: An endophenotypic marker?

Abstract

The frequency of symptomatic dystonia in relatives of patients with idiopathic focal dystonia (IFD) is higher than expected from epidemiologic studies implying that genetic factors may be involved. Perception of the vibration-induced illusion of movement (VIIM) is subnormal in patients with IFD compared with healthy volunteers and the abnormality corrects with volitional fatigue of the vibrated arm. The aim of the study was to establish the heritability of the abnormality of VIIM. The perception of illusion of movement elicited by vibration of the biceps brachii tendon before and after fatigue of the muscles was investigated in 30 patients with torticollis, 57 of their first degree relatives, and 19 healthy volunteers. VIIM did not change after fatigue in healthy controls. Before fatiguing the muscles, patients' perception of VIIM was less than healthy controls, (P < 0.01, unpaired t-test). After fatigue, the illusion of movement perceived by patients increased, so that it did not differ any more from that of the healthy control subjects (P < 0.05, repeated measures ANOVA). First degree relatives' response to vibration varied; 45% of parents, 60.7% of siblings, and 63.6% of children had an "abnormal" response to vibration compared with 21% of healthy volunteers. In contrast to patients' response, the "abnormality" did not correct after volitional fatigue of the vibrated arm. The results suggest that abnormal VIIM may represent an endophenotypic marker for IFD, which interacts with other factors including central motor learning and compensation mechanisms in the expression of the dystonic phenotype.

Sensory-motor integration in focal dystonia

“…For instance, in focal hand and cervical dystonia vibration of the muscle belly or tendon at 50-120 Hz results in a normal tonic vibration reflex (TVR), which represents the activation of muscle spindles and ɣ-motoneurons. Conversely, during the TVR the perception of real or illusory arm movements (for which a main contribution of group Ia afferents can be suggested) is abnormal (Bove et al, 2004;Frima and Grunewald, 2005;Frima et al, 2008;Frima et al, 2003;Grunewald et al, 1997;Kaji et al, 1995;Rome and Grunewald, 1999;Yoneda et al, 2000). Despite an abnormal perception of movement, the sense of position (sub-served by group II afferents) appears to be preserved, as evidenced by the ability of patients with focal dystonia to perceive the temporal difference between two passive movements .…”

Alleviating manoeuvres (sensory tricks) in cervical dystonia

“…Most patients note that they, rather than someone else, must do the touching, although in some cases a mere imagination of AM can improve the abnormal posture or movement 7 20. Proprioceptive vibration-induced illusion of movement of an artificial hand, using the rubber hand paradigm to test sensory ownership of limb, suggests that patients with focal dystonia have deficits in visual-tactile-proprioceptive integration involving the inferior parietal cortex and the cerebellum 21 22. The broad spectrum of AMs used by patients with CD and other forms of dystonia strongly suggests that a variety of sensorimotor processes are involved in mediating this phenomenon.…”

Sensory aspects of movement disorders

“…Other studies also used somatosensory-evoked potentials and transcranial magnetic stimulation to show impaired cortical somatosensory processing, abnormal sensorimotor integration, and maladaptive cortical plasticity in patients with dystonia. 97–99 Patients with focal dystonia also have decreased kinaesthetic perception to passive joint movement, 100 abnormal proprioceptive vibration-induced illusion of movements, 101–104 and impaired integration of proprioceptive input with evidence of abnormal egocentric spatial representation. 105,106 Further more, abnormal spatial discrimination, simultaneous two-point cutaneous stimuli, and impaired temporal discrimination (two stimuli at the same place separated in time), have been recorded in patients with dystonia.…”