Apathy in Parkinson's disease: diagnosis, neuropsychological correlates, pathophysiology and treatment.

Apathy has been defined as lack of motivation. It has been traditionally considered as a symptom of psychiatric disorders, such as major depression and schizophrenia, but more recently it has been recognized as a specific neuropsychiatric syndrome associated with neurodegenerative such as Parkinson's disease (PD). As a consequence the reported prevalence of apathy in PD ranges from 13.9% to 70%; the mean prevalence is 35%. Prevalence of "pure apathy" (i.e., of apathy without comorbid depression and dementia) seems to be substantially lower, from 3 to 47.9%. High levels of apathy in PD are associated with decreased daily function, specific cognitive deficits and increased stress for families. Although neuroimaging studies do not provide a unique anatomic pattern, several data suggest that the ventromedial prefrontal cortex and the basal ganglia connected through frontal-subcortical circuits, are particularly involved in the genesis of apathy. At present, there are no approved medications for the treatment of apathy in and no proof of efficacy exists for any drug in current use. Further studies and innovative pharmacologic approaches are thus needed to ameliorate our understanding and treatment of apathy in PD.