Movement perception of the tonic vibration reflex is abnormal in functional limb weakness

Introduction We tested the hypothesis that functional limb weakness is associated with possible dysfunction of the central processing of proprioceptive information, by evaluating the amount of tonic vibration reflex (TVR) and the perception of the TVR movement. Methods The study sample was 20 patients with functional weakness of the lower and/or the upper limbs and 25 healthy controls; delivery of 92-Hz transcutaneous vibration of the biceps brachii tendon of the unrestrained arm stimulated predominantly the muscle spindle afferent and elicited elbow flexion (tonic vibration reflex, TVR). Blindfolded participants had to match the final position of the vibrated arm with their contralateral tracking arm. The TVR and perception of the TVR movement were measured as angle movements of the vibrated arm and the tracking arm, respectively. Results The magnitude of the TVR of the vibrated arm and movement perception of the TVR of the tracking arm were significantly reduced in the patients compared to the controls. No correlation was found between magnitude of the TVR and perception of the TVR movement, suggesting that the abnormalities were independent of each other. Moreover, the abnormalities did not differ between the patients with/without bilateral upper limb involvement or between the affected and the unaffected side in patients with unilateral impairment, suggesting that the observed deficits are independent of motor impairment. Conclusions Proprioceptive dysfunction may underlie alterations in body movement and in sense of agency in such patients and may play a role in the pathophysiology of functional limb weakness.