Introduction: The importance of cognition in movement disorders

In the past decade, there has been an explosion in clinical attention and research on the cognitive aspects of all movement disorders. This is, in part, driven by the aging of the world’s population in developed countries, which has increased attention on neurodegenerative diseases that differentially affect the elderly, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and atypical parkinsonism (corticobasal syndrome [CBS], MSA, PSP, and SCA). Additionally, the increasing recognition of dementia with Lewy bodies (DLB) has highlighted the overlap between movement disorders and dementia. Another contributing factor is emerging data from prospective, long-term epidemiological studies that have led to a dramatic increase in estimates of cumulative dementia prevalence in PD. Finally, with the focus increasingly on those patients in the predementia stage, the scope of cognition-related clinical care and research has broadened significantly. Besides the aforementioned disorders, other movement disorders have either long been associated with frank cognitive impairment (i.e., Huntington’ disease; HD) or are increasingly recognized to be associated with mild cognitive deficits (i.e., essential tremor).