Neuroimaging outcomes associated with mild cognitive impairment subtypes in Parkinson's disease: A systematic review

Background: Mild cognitive impairment in Parkinson's disease (PD-MCI) is heterogenous and cognitive subtypes have been identified. However, the anatomo-functional bases of each subtype remain partly unknown. Objective: To propose a description of the current literature on neuroimaging findings associated with cognitive subtypes of PD-MCI. Methods: PubMed/Medline, Embase, PsycINFO and the Cochrane Library databases were searched (until April 2021). Studies comparing PD-MCI cognitive subtypes with healthy controls (HC) and PD patients with normal cognition (PD-NC) on any neuroimaging outcome were included. Results: Ten studies met the inclusion criteria. Six used structural MRI methods, two functional MRI methods, one electroencephalography and five positron or single-photon emission tomography. Most studies (n = 8) determined PD-MCI subtypes based on memory impairment and two based on executive impairment. Compared with HC and/or PD-NC, brain modifications were found in PD patients (a) with amnestic MCI and, to a lesser extent, non-amnestic MCI in occipital, parietal and temporal regions, (b) with executive MCI in frontal and striatal regions and (c) with non-executive MCI in posterior cortical regions. Conclusions: Very few neuroimaging studies have considered cognitive heterogeneity that exists within PD-MCI, making it difficult to draw robust conclusions regarding brain modifications associated with specific subtypes. Given the promising potential of neuroimaging methods in both clinical practice and research, further studies are needed to overcome the limitations of the current literature.

Automated summary

Recent studies have found that there is cognitive heterogeneity within mild cognitive impairment in Parkinson's disease, and further research is needed to explore the corresponding neuroimaging, especially in terms of brain modifications associated with specific subtypes.