Mild cognitive impairment (MCI) in early Parkinson’s disease may predict subsequent dementia, whether or not the person reverts to normal cognition, according to research published online ahead of print January 20 in Neurology.
Kenn F. Pedersen, MD, PhD
There is limited information about the incidence, persistence, and outcome of MCI due to Parkinson’s disease (PD-MCI) over time. A previous study suggested that PD-MCI in patients with newly diagnosed Parkinson’s disease predicts a highly increased risk for dementia within three years of diagnosis. Many patients with PD-MCI reverted to normal cognition during the investigation, however.
A Population-Based Cohort
Dr. Pedersen and his colleagues conducted a study to examine the incidence, progression, and reversion of MCI in patients with Parkinson’s disease over a five-year period. Patients included in the study were all participants in the Norwegian ParkWest project, an ongoing, prospective, population-based cohort study of the incidence, neurobiology, and prognosis of Parkinson’s disease. All participants were white and met diagnostic criteria for Parkinson’s disease.
Of the 212 patients recruited for the study, 196 were drug-naïve and without major depression or dementia at baseline. Among these 196 patients, 18 were rediagnosed during follow-up; as a result, 178 patients were eligible for the study.
After baseline examinations, researchers initiated dopaminergic medication and assessed patients clinically every six months. In addition, the investigators conducted standardized examinations of motor, neuropsychiatric, and cognitive function at study entry and after one, three, and five years of follow-up.
Diagnosing Parkinson’s Disease Dementia
Investigators identified patients with PD-MCI and determined dementia status using the Movement Disorder Society criteria. In addition, researchers made a diagnosis of Parkinson’s disease-associated dementia if they found evidence of cognitive decline during follow-up. Parkinson’s disease dementia exclusion criteria included comorbid conditions or disease that could cause or contribute to mental impairments. None of the participants met diagnostic criteria for dementia with Lewy bodies, Alzheimer dementia, or other dementia syndromes.
In all, 36 patients fulfilled criteria for PD-MCI at baseline. Among participants who were cognitively normal at baseline, the cumulative incidence of PD-MCI was 9.9% after one year of follow-up, 23.2% after three years, and 28.9% after five years. Also, 39.1% of patients with baseline or incident PD-MCI progressed to dementia during the five-year study period. A 59.1% rate of conversion to dementia was observed in patients with persistent PD-MCI at one year. Investigators also found that 27.8% of patients with baseline PD-MCI had reverted to normal cognition by the end of the study. Finally, PD-MCI reverters within the first three years of follow-up were at an increased risk of subsequently developing dementia, compared with cognitively normal patients.
One of the investigation’s limitations was that it had a short duration, considering the typically slow progression of Parkinson’s disease. In addition, the number of PD-MCI reverters was limited, and the cognitive test battery did not include language tests. Despite these limitations, the findings overall were valid and representative of the general population of patients with Parkinson’s disease, said the researchers.
“A remarkable observation in our study is the increased risk of dementia even in PD-MCI reverters. This [result] suggests that PD-MCI has clinical implications once diagnosed in early Parkinson’s disease,” said Dr. Pedersen and colleagues.
“This [finding] is important because patients with PD-MCI who revert to normal cognition may be excellent candidates for timely interventions to prevent progressive cognitive decline when they become available in the future.”
—Erica Tricarico
Suggested Reading
Pedersen KF, Larsen JP, Tysnes OB, Alves G. Natural course of mild cognitive impairment in Parkinson disease: A 5-year population-based study. Neurology. 2017 Jan 20 [Epub ahead of print].