Parkinson's disease (PD) is a common disease. Dementia will affect 80% of these patients during their evolution. In addition, treatments of motor signs have a potential impact on these disorders and conversely.

The purpose of this study is to show focal abnormalities in brain metabolism in the precuneus and posterior cingulate region are predictive of the onset of dementia within 2 years.

Cognitive impairment and dementia have become major factors of disability induced by Parkinson's disease. The prediction of dementia in any given patient may be useful for prognosis but also for discussion of setting up heavy therapeutic techniques, especially surgical. Currently, known predictors are disease severity, age and existence of pre-cognitive disorders; other assumptions are discussed. Among these, morphological imaging techniques (MRI) and functional techniques (MRI, PET) are proposed.

Use increasingly early of heavy, expensive and potentially ineffective surgical treatment in dementia makes it necessary to find independent, early and reliable markers of the onset of dementia in Parkinson's Disease.

Inclusion Criteria

• Male or female with Parkinson's Disease
• 45 < Age ≥ 75 years
• Parkinson's disease with clinical diagnosis made for at least 5 years (60 months)
• Patient able to perform cognitive tests in French during 1 hour 30 minutes
• Patient having provided a signed consent to participate in this trial
• Be either affiliated to, or a beneficiary of, a social security category
• Existence of caregiver at least contactable by phone

Exclusion Criteria

• Parkinson's disease diagnosed before 40 years old
• Clinical evidence for dementia or dementia criteria according to level 1 MDS-Task Force (Dubois et al. 2007)
• Atypical form of parkinsonism
• Other disease affecting the central nervous system
• Poorly controlled diabetes with glucose > 2.0 g/l or HbA1c>7,5% based on results of less than 3 months
• Taking a cholinesterase inhibitor treatment, memantine or long-term benzodiazepines other than referred hypnotic, neuroleptic
• History of surgery for Parkinson's disease or planned surgery within 6 months. Surgery is possible beyond
• Cons-indication to 3T MRI
• Inability to lie down for 60 minutes
• Legal protection
• Patient living outside the Ile-de France region

Secondary exclusion criteria

• Pregnant, breastfeeding or non-menopausal woman not taking contraception in the first 2 months of the study
• Existence of a significant brain injury on MRI
• Neuropsychological assessment at baseline showing dementia
• Fasting glucose > 1.6 g/l the day of FDG-PET