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A waitlist control group study of neurobehavioural outcome from unilateral posteroventral pallidotomy in advanced Parkinson’s disease Carr, Jason Andrew Robert


There is evidence to suggest unilateral posteroventral pallidotomy (PVP) effectively treats aspects of the motor disabilities associated with advanced Parkinson's disease. However, neurobehavioural outcome from PVP is less well understood. In particular, the possibility of uncontrolled practice effects has prevented a full accounting of the cognitive sequelae of PVP, and little research has examined the widely held belief that dementia is associated with poorer surgical outcome. To address these issues, this research investigated neurobehavioural outcome from PVP in a manner that controlled for test practice, and examined the relationship between pre-operative level of cognitive functioning and surgical outcome. Participants underwent baseline and two-month follow-up assessments. The surgery group underwent PVP (15 left, 7 right) after baseline assessment, while the waitlist group (n = 14) underwent PVP after follow-up. At follow-up, the waitlist and right PVP groups performed better than the left PVP group on verbal measures of list learning, fluency, working memory, and speeded color naming. The incidence of individual decline on these measures after left PVP was high. On retesting, the waitlist group demonstrated a mixed profile of improvement and decline on the cognitive measures, and changes were one quarter of a standard deviation or larger on one quarter of the measures. Pre-surgical level of cognitive functioning was not related to cognitive outcome. At follow-up, members of the surgery group reported lower bodily pain and better social functioning than waitlisted participants. The incidence of significant individual improvement was high for bodily pain but not social functioning. Higher pre-operative level of cognitive functioning was associated with greater improvement in social functioning, vitality and fatigue/inertia, depression/dejection, and anger/hostility. In conclusion, patients who undergo left PVP exhibit decline in circumscribed verbal abilities. Controlling for practice effects did not increase the breadth of cognitive decline evident after PVP beyond that typically reported in the literature. Lower pre-operative cognitive functioning may be associated with smaller post-surgical improvements in quality of life and mood. In future research it will be important to focus attention on outcome amongst individuals who underwent right PVP, and individuals functioning at a lower cognitive level pre-operatively.

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