ABNORMAL VESTIBULOOCULAR REFLEX CANCELLATION IN MULTIPLE SYSTEM ATROPHY AND PROGRESSIVE SUPRANUCLEAR PALSY BUT NOT IN PARKINSONS-DISEASE

We have measured the gain of the vestibuloocular reflex (VOR) in darkn ess and its cancellation by fixation in 37 patients with Parkinson's d isease (PD), 26 patients with multiple system atrophy (MSA), 11 patien ts with progressive supranuclear palsy (PSP), and 19 normal volunteers . The capacity to cancel the VOR by fixation (VOR cancellation) was si gnificantly reduced in the MSA and PSP patients compared with the PD a nd normal subjects (p < 10(-4)). A VOR cancellation < 90% (i.e., the m ean VOR cancellation of the normals 2 SD) was present in four PD patie nts, 23 MSA patients, and 11 PSP patients. This criteria distinguished PD and MSA with a 89% sensitivity and a 89% specificity. Our results demonstrate that the VOR cancellation is impaired in most patients wit h MSA and PSP but not with PD. In MSA patients, the abnormal VOR cance llation is probably not related to the nigrostriatal dopaminergic defi cit and more likely reflects a cerebellar dysfunction. Impaired VOR ca ncellation is a clinical criteria to differentiate MSA and PSP from PD .