Relationship between clinical phenotypes and cognitive impairment in Parkinson's disease (PD)
Introduction
The IPD is the second most common neurodegenerative disorder, and is characterized by bradykinesia, rigidity, and tremor. Although IPD is considered to be a movement disorder, it also involves non-motor symptoms, such as cognitive impairments, mood disorders, and autonomic dysfunctions. In a recent study of IPD, about 50% of the patients with IPD had dementia, which is 6 times higher than this rate in normal controls (Levin et al., 1992).
A few studies have investigated the relationship between presenting motor symptoms and cognitive functions. Patients whose major symptoms were bradykinesia and rigidity were more likely to have decreased cognitive functions than the patients with tremor as a main symptom (Huber et al., 1991). Gait impairment could be another predictable factor of cognitive decline in IPD. Patients with gait impairment were more likely to have cognitive impairment and dementia (Camicioli et al., 2007). However, most of the recent studies have dealt with limited motor symptoms, such as bradykinesia and rigidity in comparison with tremor, or were mainly focused on the presence or absence of gait impairment. Therefore, the previous studies had a limitation in that they simplified the clinical phenotype in IPD patients.
Although no definite relationship has been established, onset age might be related to cognitive impairment in IPD (Huber et al., 1991, Aarsland et al., 1996, Muslimovic et al., 2005). The purpose of this study was to verify the relationship between motor symptoms at the time of onset and the level of cognitive function in patients with IPD.
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Subjects
A total of 216 patients with Parkinsonian features who visited the Department of Neurology at Chungnam National University Hospital between November 2006 and June 2007 were enrolled in this study. Patients who met the established diagnostic criteria of IPD (Hughes et al., 1992) were included, and none of them took cholinesterase inhibitors. A total of 159 patients participated in the study after the exclusion of 27 patients with vascular Parkinsonism, 10 patients with normal pressure
Results
Demographics and clinical characteristics of the participants are reported in Table 1. The study population was composed of 59 men and 100 women. The mean age and mean onset age was 69.1 ± 7.8 (±S.D.) and 64.7 ± 9.2 years, respectively. The mean duration of education was 6.2 ± 5.1 years. The 159 study subjects included 64 patients with TD, 50 with BRD and 45 with GPD.
Table 2 illustrates the clinical characteristics of three groups according to their initial motor symptoms. There were no differences
Discussion
The main neuropathological change in IPD is the loss of dopaminergic neurons from the nigrostriatal tract leading to a decrease in dopamine in the striatum. The cognitive decline and motor symptoms in IPD share a common pathogenesis: both of them are caused by a decrease in dopamine from the striatum (Bernheimer et al., 1973, Brück et al., 2001). Thus, there might be a relationship between the severity of dementia and the dopamine decrease from this part. Shohamy et al. (2005) and Nagy et al.
Conflict of interest statement
None.
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