Figure 2 Overview of risk factors for Parkinson disease dementia Figure 2 | Overview of risk factors for Parkinson disease dementia. Three different categories of risk factors for Parkinson disease dementia (PDD) — clinical, molecular, and structural/functional imaging — are illustrated. Factors with evidence from longitudinal studies are shaded pink, and factors with evidence from cross-sectional studies are shaded grey. Interrelationships between factor categories (bidirectional arrows) and temporal relationships between cross-sectional factors and PDD (unidirectional arrows) remain unclear. MCI, mild cognitive impairment; MEG, magnetoencephalogram. Aarsland, D. et al. (2017) Cognitive decline in Parkinson disease Nat. Rev. Neurol. doi:10.1038/nrneurol.2017.27