The contribution of white matter lesions (WML) to Parkinson's disease cognitive impairment symptoms: A critical review of the literature.

We reviewed the impact of white matter lesions (WML) of cerebrovascular origin on cognitive impairment in Parkinson's disease (PD) patients. A search of PUBMED and Googlescholar.com revealed eleven studies that met the inclusion criteria: diagnosis based on the United Kingdom Brain Bank criteria (UK BBC); cognitive assessment; WML assessed on magnetic resonance imaging (MRI) by semiquantitative visual scales or automated method. Eight studies described the negative impact of WML on cognition in PD. Patients with mild cognitive impairment (MCI) and dementia had significantly more WML than the group without MCI and dementia. There was significant relationship between increasing total WML volume and worse performance on executive function, memory and language. Patients with vascular parkinsonism and dopaminergic denervation had more severe frontal lobe dysfunctions than patients with PD. In contrast in three studies there was no negative correlation between WML and cognition. Although the progression of neurodegenerative process in advanced stage of PD has been recognized as being mainly responsible for cognitive impairment in PD, WML may also be a contributing factor. It is possible that by reducing the vascular risk factors that cause WML cognitive impairment could be prevented or slowed down.