Montreal Cognitive Assessment Performance in Patients with Parkinson’s Disease with “Normal” Global Cognition According to Mini-Mental State Examination Score

TLDR: Examination of Montreal Cognitive Assessment performance in patients with Parkinson's disease with “normal” global cognition according to Mini‐Mental State Examination (MMSE) score finds no significant differences between the two assessments.

Abstract: Cognitive impairment insufficient to meet criteria for dementia (mild cognitive impairment (MCI)) has been reported to occur in 20% to 30% of patients with Parkinson’s disease (PD),1–5 even in newly diagnosed patients.4,5 Identification of initial impact or MCI in PD is important, because it predicts future cognitive decline, including development of PD dementia (PDD),2,3,6,7 and deterioration of health-related quality of life.8 Impairments in executive function, attention, visuospatial skills, and memory characterize the “typical” cognitive profile in PD, whereas language and praxis are thought to be relatively spared.3,4,9 The memory impairment associated with PD is classically considered a retrieval deficit (i.e., subcortical memory profile) as opposed to an encoding deficit (i.e., cortical memory profile). There is substantial overlap in the pattern of observed cognitive deficits in PD without dementia and PDD. Studies enrolling both groups of patients have shown qualitatively similar, but quantitatively greater, impairments in patients with PDD in executive function, visuospatial abilities, attention, and psychomotor skills.10 In longitudinal studies of patients without dementia at baseline, verbal memory deficits11 and executive or visuospatial impairments12 have been shown to predict development of PDD on long-term follow-up. Given the aforementioned high prevalence of MCI in PD and its association with future development of dementia, it is important that patients with PD, even those with mild disease, be screened regularly for cognitive impairment.12 An ideal cognitive screening instrument in PD should be brief, assess a range of cognitive domains, simple to administer, sensitive to the initial stage of cognitive impairment, and unaffected by motor impairment. Few screening instruments have been validated or developed to assess global cognition in PD. The Scales for Outcomes of Parkinson’s Disease—Cognition was recently developed and has been shown to be valid and reliable in differentiating patients with PD with and without dementia,13,14 but its performance, specifically in patients without significant global cognitive impairment, has not been reported. The Cambridge Cognitive Examination—Revised distinguishes between patients with PD with and without dementia and detects cognitive impairment in patients with PD with an MMSE score less than 25,15 but it takes approximately 60 minutes to administer. The Mini-Mental State Examination (MMSE)16 remains the most commonly used screening instrument for global cognition. The MMSE is used extensively in PD, but its use in this population has been questioned,17,18 in part because the MMSE primarily assesses memory and language skills and also may not be sensitive to detect many cases of MCI. The Montreal Cognitive Assessment (MoCA)19 is a new cognitive screening instrument that was designed to address some of the limitations of the MMSE. It assesses a broader range of cognitive domains than the MMSE and is more challenging from a cognitive standpoint overall. The MoCA and the MMSE both have items that require motor skills that core PD symptoms potentially affect (5/30 points on the MoCA and MMSE). The MoCA has been shown to be more sensitive than the MMSE for the detection of MCI and mild Alzheimer’s disease in the general population, and a score less than 26 was found to be the optimal cutoff point for a diagnosis of cognitive impairment.19 There have been two studies using the MoCA in PD, and in one, the MoCA was found to be more sensitive than the MMSE in detecting cognitive impairment in this population,17 although a MMSE score less than 26 was used to classify patients as having cognitive impairment, and this cutoff has not been validated for PD. In addition, the authors did not examine differences in MoCA subscores in impaired and unimpaired groups or examine correlates of MoCA performance. In the other study, the MoCA was found to have good test–retest reliability, interrater reliability, and convergent validity with a neuropsychological battery in a small sample of patients with PD.20 This study presents results on the frequency and correlates of cognitive impairment using the MoCA in patients with PD. These patients were a priori defined as not meeting criteria for global cognitive impairment when evaluated with the MMSE. It was hypothesized that a substantial proportion of patients with PD would be impaired (score <26) on the MoCA in spite of having a normal MMSE score and that cognitive impairment would occur in a range of domains, including visuospatial and executive abilities, attention, and memory.