Parkinson’s Disease and Dementia Associated with Parkinson’s Disease

Prevalence and Clinical Correlates

Apathy is the most common neuropsychiatric symptom reported in Parkinson’s disease, but its prevalence and clinical correlates are debated. Its frequency varies from 15 to 70 % [3, 15, 92-94] depending on the sample population, the assessment, and the diagnostic criteria. A mean prevalence of 30-40 % was reported in the review of Santangelo [95]. It can precede the onset of the first motor symptoms [96]. It occurs in drug-naive new-onset parkinsonian patients in 20-36 % of cases [95, 97-99]. Its prevalence seems to decrease after the introduction of dopaminergic treatment. After 5-10 years of disease curse, its frequency increases to 40 % in non-demented patients and to 60 % in demented patients [100-102].

Apathy may occur in Parkinson’s disease as a separate, isolated behavioral symptom (i.e., unrelated to cognitive impairment or depression) [103-105]. Four major subdomains of goal-directed behavior reportedly contribute to apathy [106]: reward deficiency, depression, executive dysfunction [28], and autoactivation failure. Isolated apathy has been reported at early and advanced stages of Parkinson’s disease [104,107]. A recent meta-analysis reported that apathy affects almost 40 % of patients with Parkinson’s disease [105]. Half of the patients with apathy do not suffer from concomitant depression or cognitive impairment, suggesting that it is indeed a separate feature of Parkinson’s disease.

Apathy is frequently associated with poor prognostic factors, such as older age, a lower mean mini mental state examination score, a higher Unified Parkinson’s Disease Rating Scale motor score, and more severe disability [105]. Apathetic Parkinson’s disease patients are more likely to have severe executive dysfunction and higher risk of developing dementia [108, 109]. As such, apathy is a key symptom of the worsening of the disease and is predictive of poorer functioning in activities of daily living [110], a decreased response to treatment, poor outcomes, diminished quality of life [98, 108, 111], and greater caregiver burden [112].

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