[Depression and apathy in Parkinson disease].

Although Parkinson disease (PD) is primarily a condition of motor symptoms, an increasing amount of research has indicated that non-motor symptoms including cognitive and emotional deficits are observed even in the earliest stage of the disease. Individuals with PD may display various psychiatric and/or behavioural problems, among which depression and apathy are the most prominent symptoms. Prevalence of comorbid depression in PD has reportedly been estimated to be 7-76%. Such marked differences in the prevalence is partially attributable to different diagnostic criteria. It is useful to make a diagnosis according to standardized semi-structured diagnostic interview following DSM-IV or ICD-10. Based on such diagnostic criteria, prevalence of depression may approximate 20-40%. A half of such individuals fulfill the criteria of major depressive disorder while remaining half may be diagnosed as having dysthymia, minor depression or apathy. The second reason contributing to diversity of prevalence of depression in PD is a sampling procedure. Prevalence of depression in PD is much lower in the community-based surveys than those examined recruited patients. The third reason which makes the diagnosis of depression in PD difficult is an approach how to treat ambiguous symptoms. Caution should be paid whether the researcher is taking an inclusive or exclusive approach while they diagnose depression in PD. Concerning apathy in PD, one should be aware that typical apathy syndrome is quite different from depressive mood state. Rather, apathy syndrome is on the opposite side of depression in the sense that the former lacks serious self reproach or feeling of guilty. Neural substrate of apathy is known to include the dorsolateral, medial and orbital frontal cortices, and subcortical structures such as the basal ganglia, thalamus and internal capsule. Future researches are warranted that discriminate neural correlates and/or chemical neurotransmitters between depression and apathy.