Background: Little is known regarding the cognitive impairment in subjects with early, drug-naive Parkinson disease (PD). The aim of this study was to explore the proportion with mild cognitive impairment (MCI) and subtypes in an incidence cohort of untreated PD in Southern and Western Norway.
Methods: A total of 196 non-demented, drug-naive patients who were recruited after an extensive search of all new cases of PD in the area and 201 healthy control subjects completed a battery of neuropsychological tests of verbal memory, visuospatial, and attentional-executive functioning. Subjects were classified as MCI if the age-and education-corrected z-score was falling 1.5 standard deviations below the mean for at least one of the cognitive domains.
Results: The PD group was more impaired on all neuropsychological tests than controls, but the effect sizes were small. The largest effect size was found for verbal memory. A total of 18.9% of the patients with PD were classified as MCI, with a relative risk of 2.1 (1.2–3.6) in PD compared to the control group. Patients with PD with and without MCI did not differ significantly regarding demographic and motor features. Among PD-MCI patients, nearly two-thirds had a non-amnestic MCI subtype, and one third had an amnestic MCI subtype.
Conclusions: The findings demonstrate a twofold increase in the proportion with cognitive impairment in subjects with early, untreated Parkinson disease (PD) compared to controls. This has implications for diagnosis and management of PD.
A number of previous studies have reported the presence of higher rates of patients with Parkinson’s disease with mild cognitive impairment (MCI) in the early stage of the disease. As a number of methodological issues may influence this finding Aarsland et al in 2009 investigated the presence of MCI using the published consensus criteria for dementia in PD, proposed by the Movement Disorders Society (Emre et al Movement Disorders 2007). These criteria exclude the possibility that cognitive decline in PD is due to drug treatment or depression. The authors, in their study published in 2009 in Neurology, investigated the frequency and the clinical features of mild cognitive impairment in a population of 196 unselected, untreated patients without major depressive disorders with Parkinson’s disease (PD), from Norway and 201 healthy control group with a battery of neuropsychological tests assessing verbal memory, visuospatial and attentive-executive functioning. Aarsland et al found that at time of diagnosis PD patients have a twofold increased risk for MCI in comparison to normal subjects. Approximately 20 % of the PD group had MCI. A non-amnestic MCI subtype was more common than an amnestic MCI subtype. This paper clearly suggests that in PD cognitive impairment is already present from the time of diagnosis. One important issue that needs further investigations is the significance of this result in terms of the risk for developing dementia. The demonstration that MCI may be present in the early stage of the disease has important implications for the management of Parkinson’s disease and for possible therapeutical interventions.
Alfredo Berardelli is Professor of Neurology at the University of Rome Sapienza and former President of the MDS-ES