Eye movement deficits in X-linked dystonia-parkinsonism are related to striatal degeneration

Background: X-linked dystonia-parkinsonism (XDP) is characterized by the unique transition of dystonia to parkinsonism and striatal degeneration. Slowing of saccades on clinical examination has been taken as suggestive of a progressive supranuclear palsy (PSP) phenotype. Objectives: To elucidate whether eye movement abnormalities in XDP patients reflect striatonigral impairment or deficits in the brainstem saccade generator as present in PSP. Methods: Eye movements of 18 male XDP patients from the Philippines and 16 ethnically and age-matched, healthy control participants were analyzed and the results related to morphometric frontostriatal changes. Results: There was moderate saccade hypometria in XDP but velocity of visually guided saccades was normal. XDP patients showed an increased antisaccade error rate which correlated with the reduction of (i) the volume of the pallidum and putamen as well as (ii) the volume and cortical thickness in dorsolateral prefrontal cortex. Amplitude of memory-guided saccades was smaller and latency prolonged. Horizontal smooth pursuit eye movements were impaired. Conclusions: Oculomotor abnormalities in XDP resemble those of patients with the Parkinsonian type of multiple system atrophy and - to a lesser degree - Parkinson's disease, but are not compatible with PSP. They indicate striatal impairment and may represent preclinical signs of the parkinsonian stage of XDP. The increasing failure of response inhibition in the antisaccade task with increasing striatal atrophy may indicate an endophenotype for striatal degeneration. Dorsolateral prefrontal degeneration can be inferred from the failure in initiating anti saccades, prolonged latency of memory-guided saccades and the reduction of dorsolateral prefrontal volume and cortical thickness.