There are few epidemiological studies of neuropsychiatric symptoms in parkinsonian disorders. In one study of a relatively large, representative community-based sample of patients with PD, 61% had a positive score on at least one NPI item, and 45% had a positive score on at least two items. Patients in nursing homes, with more advanced parkinsonism, and with dementia had more frequent and severe neuropsychiatry symptoms (12). Studies of patients with atypical parkinsonian disorders have typically involved small convenience samples from highly specialized movement disorder clinics, and thus may not necessarily be representative of the general population. The exception is DLB, and two studies, both including 98 patients with DLB, showed a high prevalence of neuropsychiatric symptoms (23,24). In one study, 98% had at least one positive symptom as measured by the NPI (24) demonstrating the importance of neuropsychiatric symptoms in this common disorder, which affects 5% of the elderly aged 75 or more (25). Unlike other dementias, neuropsychiatric symptoms in DLB are not associated with declining cognition (23), nor with age or gender (26). In PSP, 88% of patients had at least one positive NPI item (27) and 87% of CBD patients (28), again underlining the importance of neuropsychiatric symptoms in patients with parkinsonian disorders. In PSP and CBD, there is little correlation between neuropsychiatric symptoms and motor and cognition scores, indicating that in these disorders, the frontosubcortical circuits mediating behavior and motor symptoms degenerate independently.
What are the clinical implications of neuropsychiatric symptoms in patients with parkinsonian disorders? Again, most research has been performed on patients with PD, and it seems reasonable to extrapolate the findings from these studies to patients with atypical parkinsonian disorders. First, several studies have consistently demonstrated that neuropsychiatric symptoms have strong negative influences on the quality of life, including physical, social, and psychological well-being of patients with PD, even after controlling for motor, functional, and cognitive disturbances. For instance, depression has consistently, and irrespective of instruments used to assess depression, been found to be among the most important independent predictors of impaired quality of life in PD patients (29-31), and a longitudinal study reported that depression and insomnia were the most important factors associated with poor quality of life (32). Although there is overlap between the symptoms of depression and quality of life, these findings highlight the need to diagnose and treat depression in patients with parkinsonian disorders.
Second, caring for a patient with a parkinsonian disorder is associated with considerable emotional, social, and physical distress (33-35). Neuropsychiatric symptoms of PD patients, such as depression, cognitive impairment, delusions, and hallucinations, have been found to be significant and independent contributors to the perceived burden in spouses of these patients (33). Third, a substantial proportion of patients with parkinsonian disorders are admitted to nursing homes (36). In addition to motor symptoms and functional impairment, neuropsychiatric symptoms such as cognitive impairment and psychosis have been found to be independent predictors of nursing home admission in parkinsonsian patients (37,38). Both higher need for care and increased caregiver burden may contribute to the relationship between nursing home admission and neuropsychiatric symptoms. Fourth, neuropsychiatric symptoms may increase the economic costs in patients with parkinsonism. In a recent study of patients with Alzheimer's disease (AD), health-related costs were substantially higher in patients with higher scores on the NPI compared to those with low levels (39), and a similar relationship may exist in patients with parkinsonian disorders as well. Finally, there is some evidence that neuropsychiatric symptoms are associated with a more severe disease course. PD patients with depression have been related to a more rapid cognitive decline (40), although other studies have not found a relationship between neuropsychiatric symptoms and cognitive decline (41) or mortality (42). In summary, the importance of neuropsychiatric symptoms for the quality of life and prognosis of patients with parkinsonian disorders, perceived stress of their spouses as well as the need for health care resources is well established, highlighting the need for proper diagnosis and management of these aspects of the parkinsonian disorder.
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