Defining Mild Cognitive Impairment in Parkinson’s Disease John N. Caviness, MD, 1 * Erika Driver-Dunckley, MD, 1 Donald J. Connor, PhD, PhD, 2 Marwan N. Sabbagh, MD, 2 Joseph G. Hentz, MS, 3 Brie Noble, BS, 3 Virgilio Gerald H. Evidente, MD, 1 Holly A. Shill, MD, 2 and Charles H. Adler, MD, PhD 1 1 Department of Neurology, Mayo Clinic, Scottsdale, Arizona 2 The Cleo Roberts Center for Clinical Research, Sun Health Research Institute, Sun City, Arizona 3 Section of Biostatistics, Mayo Clinic, Scottsdale, Arizona Abstract: Our purpose was to characterize a state of mild cognitive impairment (MCI) in Parkinson’s disease (PD) (PD- MCI) that would be analogous to the MCI that is posited as a precursor of Alzheimer’s disease (AD). We categorized 86 PD subjects in a brain bank population as either cognitively normal (PD-CogNL), PD-MCI using criteria that included a 1.5 stan- dard deviation or greater deficit upon neuropsychological test- ing consistently across at least one cognitive domain without dementia, and PD dementia (PD-D) using DSM-IV criteria. Twenty-one percent of our PD sample met criteria for PD-MCI, 62% were PD-CogNL, and 17% had PD-D. The mean duration of PD and MMSE scores of the PD-MCI group were interme- diate and significantly different from both PD-CogNL and PD-D. The cognitive domain most frequently abnormal in PD-MCI was frontal/executive dysfunction followed by am- nestic deficit. Single domain PD-MCI was more common than PD-MCI involving multiple domains. We conclude that a stage of clinical cognitive impairment in PD exists between PD- CogNL and PD-D, and it may be defined by applying criteria similar to the MCI that is posited as a precursor of AD. Defining PD-MCI offers an opportunity for further study of cognitive impairment in PD and targets for earlier therapeutic intervention. © 2007 Movement Disorder Society Key words: mild cognitive impairment; dementia; Parkin- son’s disease Cognitive impairment is common in Parkinson’s dis- ease (PD) and can range from mild impairment to florid dementia. It is estimated that 30% to 40% of PD patients eventually suffer from dementia. 1 Beside the disability it creates, dementia doubles the mortality risk of PD and increases nursing home placement. 2,3 Neuropsychologi- cal testing abnormalities in non-demented PD patients have been reported to be predictive of dementia devel- opment, but the types of abnormalities reported vary. 1,4-7 Most reports mention impairments in executive function or memory as predictive of dementia development while others mention visuospatial dysfunction. 4,6,7 The construct of mild cognitive impairment (MCI) as a precursor to Alzheimer’s disease (AD) has created a new area of research for AD and a potential new target for therapeutic intervention. Therapeutic intervention at this earlier stage may be more effective at slowing dis- ease progression than when dementia is fully developed. 8 While Petersen’s original construct involved a singular memory deficit (amnestic-MCI), more recent iterations have included deficits in memory and other domains (multiple-MCI), or domains other than memory (non- amnestic-MCI), allowing for the possibility that this pro- cedure may be applicable to other dementias as well. Although multiple investigators have studied cognitive impairment in non-demented PD patients, defining the quantitative and qualitative aspects of a defined MCI state in PD has received little attention. 6 Defining MCI in PD (PD-MCI) should create an opportunity for studying the pre-dementia state in PD and allow targeting of PD cognitive decline at an earlier stage. Therefore, the ob- jective of this article is to apply a set of criteria for cognitive impairment based on the Petersen et al. criteria for MCI to our sample of patients with PD and to report its properties. *Correspondence to: Dr. John N. Caviness, 13400 East Shea Blvd., Scottsdale, AZ, 85259. E-mail: jcaviness@mayo.edu Received 19 October 2006; Revised 21 December 2006; Accepted 1 February 2007 Published online 5 April 2007 in Wiley InterScience (www. interscience.wiley.com). DOI: 10.1002/mds.21453 Movement Disorders Vol. 22, No. 9, 2007, pp. 1272–1277 © 2007 Movement Disorder Society 1272