The presence of mild cognitive impairment (MCI) in PD is associated with subsequent dementia.1,5 Cognitive impairment reduces overall quality of life and may ultimately require an affected individual to be placed in a nursing home.1 MCI is common among people with PD; a large meta-analysis identified 41 studies of the prevalence and clinical aspects of MCI in Parkinson’s disease, with a pooled incidence prevalence of 40% (95% confidence interval: 36–44%).4
A community-based study carried out in Cambridgeshire, UK, recruited new cases of PD and followed them over several years to identify factors associated with the later development of dementia.2 In addition to older age, risk factors included a non-tremor-dominant motor phenotype, more severe motor symptoms, and poorer performance on various cognitive function tests (semantic fluency; pentagon copying; spatial recognition memory; and executive function).2 Patients with a non-tremor-dominant motor phenotype were >4 times more likely to develop dementia than tremor-dominant patients, perhaps reflecting the faster progression of PD in the former group.2 Although smaller-scale studies such as the longitudinal analysis following 36 people for 20 years summarized on the slide have suggested a lower incidence of dementia in PD than have been found in other studies, there is a risk of survivor bias in such studies.3