Mild Cognitive Impairment in Parkinson’s Disease—What Is It?

PURPOSE OF REVIEW Mild cognitive impairment is a common feature of Parkinson's disease, even at the earliest disease stages, but there is variation in the nature and severity of cognitive involvement and in the risk of conversion to Parkinson's disease dementia. This review aims to summarise current understanding of mild cognitive impairment in Parkinson's disease. We consider the presentation, rate of conversion to dementia, underlying pathophysiology and potential biomarkers of mild cognitive impairment in Parkinson's disease. Finally, we discuss challenges and controversies of mild cognitive impairment in Parkinson's disease. RECENT FINDINGS Large-scale longitudinal studies have shown that cognitive involvement is important and common in Parkinson's disease and can present early in the disease course. Recent criteria for mild cognitive impairment in Parkinson's provide the basis for further study of cognitive decline and for the progression of different cognitive phenotypes and risk of conversion to dementia. Improved understanding of the underlying pathology and progression of cognitive change are likely to lead to opportunities for early intervention for this important aspect of Parkinson's disease.