Prediction of Dementia in Parkinson's Disease by Measuring Cerebral Metabolism With PET Scan

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