Mild cognitive impairment is common in Parkinson's disease patients with normal Mini-Mental State Examination (MMSE) scores

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Abstract

Purpose

Cognitive impairment occurs in the majority of Parkinson's disease (PD) patients, but little is known about detection of mild cognitive impairment (MCI) in this population. We report on the frequency and characteristics of cognitive deficits in PD patients with intact global cognition based on Mini-Mental State Examination (MMSE) performance.

Methods

One hundred and six PD patients with normal age- and education-adjusted MMSE scores (mean [SD] score = 29.1 [1.1]) were administered standardized neuropsychological tests assessing memory, executive function, and attention. Impairment on a cognitive domain was a low score (i.e., ≥1.5 SD below the published normative mean) on at least two measures or tests (for memory and executive abilities) or a single measure (for attention).

Results

Mild cognitive impairment was found in 29.2% of PD patients, with 17.9% demonstrating single domain and 11.3% multiple domain impairment. Memory and attention impairment were most common (15.1% and 17.0%, respectively), followed by executive impairment (8.5%). Depending on the measure of disease severity chosen, increasing age and disease severity, anti-anxiety medication use, and a suggestion for increasing severity of daytime sleepiness were independent predictors of cognitive impairment.

Conclusions

Cognitive deficits are common in PD patients with “normal” cognition based on MMSE performance, suggesting that MCI is under-recognized in clinical practice due to routine use of insensitive screening instruments. In contrast with some previous reports, early memory impairment may be as common as either executive or attentional deficits in PD. In addition, psychiatric medication use and daytime sleepiness may be reversible or treatable contributors to cognitive impairment.

Introduction

Cognitive impairment in the absence of frank dementia, typically called mild cognitive impairment (MCI), occurs frequently in Parkinson's disease (PD) [1], [2], even among those newly diagnosed [3], [4]. Impairments in executive function, attention, visuospatial skills and memory have all been reported, whereas language and praxis are thought to be relatively spared [3], [5]. When a discrepancy in cognitive performance has been reported, greater impairment has been found on executive measures than memory measures [6], [7].

Identification of MCI in PD is important, as it predicts future cognitive decline [2], [5], [8] and may eventually be a target for pharmacologic intervention to prevent or delay the development of dementia. Given the common occurrence of a range of cognitive deficits at all stages of PD, routine cognitive screening of all PD patients with a sensitive assessment is important.

The Mini-Mental State Examination (MMSE) [9] remains the “gold standard” screening instrument for global cognition. The MMSE is used extensively in PD, but its use in this population has been questioned [10], [11], both because the MMSE assesses primarily memory and language skills (i.e., not broad enough), and because it may not be sensitive enough to detect many cases of MCI (i.e., instrument ceiling effect).

Given the existing limitations in our knowledge of MMSE performance in PD, we present results on the frequency and correlates of cognitive impairment in PD patients with intact global cognition based on MMSE performance.

Section snippets

Subjects

The study population consisted of a convenience sample of idiopathic PD patients recruited from movement disorders centers at the University of Pennsylvania and the Philadelphia Veterans Affairs Medical Center. Subjects completed an extensive psychiatric, neuropsychological, and neurological battery as part of a study on the frequency and correlates of psychiatric and cognitive complications in PD. The neuropsychological battery was chosen to focus on memory and executive function abilities,

Frequency of impairment by neuropsychological test

Memory domain impairment was found in 15.1% of subjects, with 21.7%, 20.8%, and 14.2% demonstrating impairment on free recall, retention, and recognition discrimination subtests, respectively (Table 2). Executive function domain impairment was found in 8.5% of subjects, with 15.1% impaired on the TOL-DX, 11.3% on the STRP, and 7.5% on verbal fluency. Lastly, 17.0% of patients were impaired in attention, with 17.0% impaired in the backward digit span and 0.9% on the forward digit span.

Frequency of impairment by cognitive domain

A total of

Discussion

We found that mild cognitive impairment, either in single or multiple cognitive domains, occurs in almost one-third of PD patients with intact global cognition as defined by a normal score on the MMSE. In addition, memory deficits, including retrieval deficits, are as common as executive function and attention deficits at the initial stage of cognitive impairment. Finally, anti-anxiety medication use and excessive daytime sleepiness may be reversible or treatable contributors to mild cognitive

Acknowledgment

Funded in part by NIMH grant #067894.

References (43)

  • M.F. Folstein et al.

    “Mini-Mental State”: a practical method for grading the cognitive state of patients for the clinician

    J Psychiatr Res

    (1975)
  • C. Zadikoff et al.

    A comparison of the mini mental state exam to the montreal cognitive assessment in identifying cognitive deficits in Parkinson's disease

    Mov Disord

    (2007)
  • R.J. Athey et al.

    Cognitive assessment of a representative community population with Parkinson's disease (PD) using the Cambridge Cognitive Assessment-Revised (CAMCOG-R)

    Age Ageing

    (2005)
  • M. Folstein et al.

    The meaning of cognitive impairment in the elderly

    J Am Geriatr Soc

    (1985)
  • R.M. Crum et al.

    Population-based norms for the Mini-Mental State Examination by age and educational level

    JAMA

    (1993)
  • K.E. Schmader et al.

    Medication use patterns among demented, cognitively impaired and cognitively intact community-dwelling elderly people

    Age Ageing

    (1998)
  • J. Brandt et al.

    The Hopkins verbal learning test—revised

    (2001)
  • C. Golden

    The Stroop color and word test

    (1994)
  • J.A. Gladsjo et al.

    Norms for letter and category fluency: demographic corrections for age, education, and ethnicity

    Assessment

    (1999)
  • W.C. Culbertson et al.

    Tower of London-Drexel (TOLDX), technical manual

    (2005)
  • Comprehensive norms for an expanded Halstead-Reitan battery: demographic corrections, research findings, and clinical applications

    (1991)
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