Neuroimaging of nonmotor features of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor symptoms that respond to dopaminergic therapy. However, there is increasing interest in nonmotor PD features such as hyposmia, sleep disorders, dementia, depression, and psychoses. We review neuroimaging studies in nonmotor symptoms of PD and the use of dopaminergic imaging to support screening of nonmotor symptoms for early PD. Neuroimaging data document nonmotor pathophysiologic involvement of systems beyond the nigrostriatal dopaminergic pathway. These neuroimaging studies support a broader view of PD with early involvement in time and wider involvement of monoamine and cortical systems that may provide targets for novel therapies for nonmotor symptoms.