Cognitive reserve in Parkinson's disease: a systematic review and meta-analysis

Background: The concept of cognitive reserve is proposed to explain the mismatch between the degree of pathological changes and their clinical manifestations and has been used to help understand the variation in the rate of cognitive decline and the development of dementias. It is not clear whether this concept applies to cognitive performance, cognitive decline and dementia in Parkinson's disease (PD).

Methods: A systematic review was conducted using the most commonly described proxies for cognitive reserve of education, occupation and leisure activities. Thirty four papers were found on education and cognition in PD but there were no studies of the other proxies of reserve. A random effects meta-analysis was used to assess the associations between education and cross-sectional cognitive assessments, longitudinal global cognitive decline and a long term dementia diagnosis.

Results: There was a significant association between higher education and cross-sectional performance of MMSE, global cognition, mild cognitive impairment, attention, executive function, visuospatial function and memory. There was a small but significant association between higher education and a reduced rate of cognitive decline. There was no association with a final dementia diagnosis. There was not enough information to perform an analysis on the rate and timing of transition to dementia.

Conclusions: Higher levels of education are associated with significantly better cognitive performance and a small but significant slowing in cognitive decline but are not associated with a reduction in long-term dementia in PD. More detailed, standardized, longitudinal studies are required to study conclusively the effects cognitive reserve in PD.