Case studies in the advancement of Parkinson's disease.

: Parkinson's disease is the second most common neurodegenerative disease following Alzheimer's disease. As there is no biomarker or diagnostic test available for the diagnosis of Parkinson's disease, diagnosis of this disorder can be challenging. Parkinson's disease symptoms include both motor and non-motor symptoms. Non-motor symptoms may require special attention, such as the impulse control disorders that can be devastating to patients and their families. This Expert Review Supplement presents three cases that illustrate different aspects of Parkinson's disease, including diagnosis, non-motor symptoms, and treatment.