Dopaminergic function and progression of Parkinson's disease: PET findings.

Recent PET studies in Parkinson's disease (PD) have shown that the progression of neurodegeneration follows an exponential decay pattern. Most of the damage to the nigrostriatal dopamine system occurs during the presymptomatic phase of the disease and the first few years following symptom onset. The progressive loss of dopaminergic neurons is accompanied by several functional adaptive changes in surviving nerve terminals, which lead to increased dopamine turnover and raise the risk of treatment-related motor complications. Younger PD patients seem to have more efficient compensatory mechanisms and a slower rate of progression of neurodegeneration.