Abnormal perception of vibration-induced illusion of movement in dystonia

Objectives: To examine the illusional sensation of movement evoked by vibra tion of an immobilized arm. Methods: Patients with idiopathic focal dystoni a were compared with those with idiopathic PD and with patients with dyston ia secondary to PD. A 100-Hz transcutaneous vibratory stimulus was applied to the biceps brachii tendon to elicit an illusional sensation of arm exten sion. Blindfolded patients were instructed to copy any perceived movement o f the vibrated arm with the opposite (tracking) arm. By recording movement of reflective markers on the tracking arm using infrared video cameras, the change in elbow angle was quantified over 45 seconds. The effect of treatm ent with botulinum toxin was examined by retesting previously untreated pat ients after commencing therapy. These results were also compared with patie nts with hemifacial spasm who had ongoing treatment with botulinum toxin. R esults: Vibration of the biceps in dystonic patients produced a smaller sen sation of arm extension than in control subjects unaffected by botulinum to xin treatment. There were no differences between the types of idiopathic fo cal dystonia examined, including patients with dystonia in sites other than the arm. Those with idiopathic PD and hemifacial spasm did not differ from healthy control subjects. Patients with dystonia secondary to PD showed a unilateral abnormality on the side of dystonic symptoms. Conclusion: Bilate ral abnormal perception of the illusion of vibration-induced movement is a feature of idiopathic focal dystonia but not idiopathic PD, and is independ ent of treatment with botulinum toxin. Unilateral, abnormal sensorimotor in tegration is implicated in dystonia secondary to PD. These results may refl ect abnormal sensorimotor integration of Ia afferent activity.