Effects of PR Oxycodone and of Levodopa, vs Placebo, on Central Neuropathic Pain in Parkinson's Disease

Inclusion Criteria: * Patients with Parkinson's disease according to the UKPDSBB (United Kingdom Parkinson's Disease Society Brain Bank) criteria * Patients suffering from chronic pain (lasting for more than 3 months) * Patients suffering from central neuropathic pain caused by PD, * Patients with a PD-related central neuropathic pain intensity of at least 3 points on the VAS (average intensity over the last month), * Patients with both types of pain (neuropathic and nociceptive) will be included if the neuropathic pain predominates * Patients treated with a stable regimen of dopaminergic drugs (levodopa and/or dopamine agonists) for at least 4 weeks before the study dan throughout the study * Patients with a stable step 1 analgesic (NSAIDS, acetaminophen) or coanalgesic (antidepressants, antiepileptic) treatment for at least 4 weeks before the study and throughout the study Exclusion Criteria: * Patients suffering from another parkinsonian syndrome * De Novo patients (patients never before treated with dopaminergic drugs) * Patients with intercurrent acute pain * Patients suffering from a chronic disease causing pain (rheumatoid arthritis, ankylosing spondylitis, diabetic neuropathy, cancer etc.) * Patients treated with neuroleptics * Patients with clinically detectable behavioural disorders and addiction * Patients with disabling dyskinesias * Patients with painful restless legs syndrome * Patients with cognitive impairment (MMS \< 25) or unable to complete the various s…