Plasticity of static graviceptive function in patients with cervical dystonia

•Patients with CD exhibit altered static graviceptive perception.•Modification of the somatosensory input can reverse this deficit in a short-term.•Modification of the proprioceptive input can reverse this deficit in a long-term.

ObjectiveBotulinum toxin (BoNT) is effective in improving abnormal head posture in cervical dystonia (CD) within a period of several weeks to an upright position. These dynamic alterations over time represent a unique model to study the plasticity of static graviceptive function in CD by assessing the subjective visual vertical (SVV).MethodsSVV was assessed in 30 CD patients and 13 controls, in their habitual head posture and with fixed head positions at different angles of head tilt. The patients were tested before and 3 weeks after BoNT administration.ResultsAt baseline, the patient's estimates in their habitual head posture and at forced head tilt angle of 30° differed significantly from those of controls. This effect was no longer visible after BoNT injection, or when the patient's head was fixed in an upright, and at a 15° head tilt position, respectively. A moderate positive correlation between disease severity and SVV aberrations was found. When comparing within-group changes, in all participants significant aberrations occurred when the head was tilted at 30°, which may be explained by the physiological E-effect.ConclusionOur findings demonstrate that patients with CD exhibit altered static graviceptive perception when tested in their habitual head posture and an overshooting E-effect at the major forced head tilt of 30°. This graviceptive perceptual deficit can be reversed by modification of the somatosensory input (i.e. head fixation) as a short-term effect, and by changes in the proprioceptive input (i.e. BoNT injections) as a long-term effect.