Mild cognitive impairment in Parkinson's disease (PD-MCI) is the highest risk factor for Parkinson's disease dementia (PDD). The core feature for differentiating PDD from PD-MCI is the loss of the ability to perform activities of daily living (ADL). As Parkinson's Disease (PD) is primarily a movement disorder, the distinction between motor and cognitive contributions to ADL in PD is an obvious challenge, which the investigators aimed to explore in this study. The goal of the study is to evaluate whether PD-MCI patients with more pronounced, cognitive-driven ADL impairment are at higher risk for cognitive worsening and PDD. A longitudinal follow-up assessment of 262 non-demented PD patients will be conducted over the next two years, with a comprehensive clinical assessment as well as biomarker sampling (cerebrospinal fluid and blood markers). Primary longitudinal outcome will be conversion to PDD and PD-MCI. Conversion rates of patients with and without additional mild cognitive-driven ADL impairment at baseline will be compared. Novel scores of the Pfeffer Functional Activities Questionnaire (FAQ) are used to assess instrumental ADL, differentiating between cognitive- and motor-driven ADL impairment in PD-MCI.

Inclusion Criteria:

• Participation in the baseline assessment
• Ability to communicate well with the investigator, to understand and comply with the requirements of the study.
• Provide written informed consent to participate in the study and understand their right to withdraw consent at any time without prejudice to future medical care.

Exclusion Criteria:

• Any disability that may prevent the subject from completing the informed consent form or other study requirements.
• Other neurodegenerative disease which renders the subject unable to communicate well with the investigator or to understand and comply with the requirements of the study.
• Participation in any clinical investigation of a new investigational compound or therapy within 4 weeks prior to baseline visit, and for any other limitation of participation based on local regulations.
• Alcohol, medication or drug dependency or abuse (except for nicotine).
• History of brain disease other than PD, e.g. head trauma, stroke, encephalitis, etc.

Participants of the already recruited ABC-PD (Amyloid-Beta in cerebrospinal fluid as a risk factor for cognitive dysfunction in Parkinson's Disease) cross-sectional cohort (Ethic Protocol of the Medical Faculty Tuebingen 686/2013B01) will be asked to participate in the follow-up assessment. A drop-out rate of 20% is expected for follow-up retention. Therefore, investigation of 209 patients will be conducted between August 2018 and April 2020.