Head deviation in progressive supranuclear palsy: enhanced vestibulo-collic reflex or loss of resetting head movements?

It is unclear how the torticollis occasionally observed in patients with progressive supranuclear palsy (PSP) relates to vestibulo-collic reflex mechanisms. We report here the results of vestibular evoked myogenic potentials (VEMPs) in a PSP patient with forced head deviation in the opposite direction of turning, leading to torticollis for a few seconds. As VEMPs were normal bilaterally we conclude that an enhanced vestibulo-collic reflex per se is not the cause of the torticollis in our patient. The abnormal head deviation induced by turning in some PSP patients is best explained by damage to reticular nuclei responsible for resetting eye and head saccades. When such mechanisms are defective, unopposed vestibulo-collic reflexes can lead to eye and head deviations in the opposite direction of body turns.