BDNF and Parkinson disease: Reported primary or secondary outcomes and employed measurement instruments fell into all domains of health-related outcomes [45], ranging from physiological/biological variables (e.g., neuroprotective markers, brain-derived growth factor (BDNF) [29] or multimodal brain imaging [35], over symptom status (e.g., Apathy Scale) [29], functional status (e.g., Berg Balance Score (BBS) [34], general health behaviors (e.g., Brief Cope Scale) [25] to overall (e.g., Short Form 36 (SF-36)) [26] or health-related quality of life (e.g., Parkinson’s Disease Questionnaire-39 (PDQ-39)) [31].