About 46% of patients suffering from Parkinson's disease present pain disorders. Parkinson disease is characterized by loss of dopaminergic neurons. The aim of this study is to assess the relationship between the loss of dopaminergic neurons and the existence of pain in Parkinson's disease. Using single photon emission computerized tomography (SPECT) imaging (123I FP-CIT, which binds dopamine transporter) and the determination of subjective pain threshold, the investigators will establish correlations between dopaminergic degeneration and pain perception.