Alterations of eye movements in Parkinson's disease with high frequency subthalamic nucleus deep brain stimulation

Objectives: High frequency deep brain stimulation (DBS) of the subthalamic nucleus (STN) has shown to be highly effective in reducing levodopa sensitive parkinsonian motor symptoms. Furthermore recent studies suggest that the STN is also involved in the control of eye movements. However, an affectation of frontobasal non dopaminergic pathways is considered to be responsible for some aspects of oculomotor dysfunction in IPD as well. We wondered if a registration of eye movement via videooculography (VOG) in DBS patients in the “on“ and “off“ state could elicit a more precise classification of eye movement changes in IPD.

Materials and methods: 15 IPD patients with DBS were examined in the “on“ and “off“ state by use of video-oculography and compared to 39 healthy controls and 24 IPD patients without DBS. For statistical analysis, all VOG parameters were subjected to an ANOVA analysis and suspected differences between the groups were analyzed with the Mann-Whitney-U test.

Results: In comparison to normal controls, all groups of IPD patients showed a reduced maximal velocity of reactive saccades. A minor improvement in the maximal velocity of reactive saccades could be detected in the DBS group in the “on“ state in comparison to “off“ state and to non DBS patients, respectively. VOG, however, showed no additional significant differences among the groups, neither for the comparison of IPD patients with and without DBS nor for DBS patients comparing the “on“ and “off“ state.

Conclusion: Our data suggest that DBS of the STN causes no significant improvement of oculomotor function in IPD. In conclusion, an alteration in the interplay of a cerebral network involving non dopaminergic frontobasal pathways has to be hypothesized to be responsible for oculomotor deficits in IPD. Further studies, preferentially with functional imaging and neuropsychologic assessment, are required to subdivide the brain structures and mechanisms which might play a major role in the pathology of eye movement in IPD as well as in neuropsychologic alterations in DBS patients.