Abnormal perception of vibration-induced illusion of movement in dystonia

To examine the illusional sensation of movement evoked by vibration of an immobilized arm.

Patients with idiopathic focal dystonia were compared with those with idiopathic PD and with patients with dystonia secondary to PD. A 100-Hz transcutaneous vibratory stimulus was applied to the biceps brachii tendon to elicit an illusional sensation of arm extension. Blindfolded patients were instructed to copy any perceived movement of 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 treatment with botulinum toxin was examined by retesting previously untreated patients after commencing therapy. These results were also compared with patients with hemifacial spasm who had ongoing treatment with botulinum toxin.

Vibration of the biceps in dystonic patients produced a smaller sensation of arm extension than in control subjects unaffected by botulinum toxin treatment. There were no differences between the types of idiopathic focal 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.

Bilateral abnormal perception of the illusion of vibration-induced movement is a feature of idiopathic focal dystonia but not idiopathic PD, and is independent of treatment with botulinum toxin. Unilateral, abnormal sensorimotor integration is implicated in dystonia secondary to PD. These results may reflect abnormal sensorimotor integration of Ia afferent activity.