PET study on striatal dopamine D2 receptor changes during the progression of early Parkinson's disease.

[11C]Raclopride uptake to dopamine D2 receptors was investigated with positron emission tomography (PET) in patients with early Parkinson's disease at the time of the diagnosis and after a half-year interval. During this progressive period of the disease, the patients received no antiparkinsonian medication. The upregulation of striatal D2 receptors, which was seen in all patients already at the time of the diagnosis, persisted. Although the patients initially showed unilateral disease, they had developed bilateral symptoms by the time of the second PET scan, but the disease was still asymmetric. The present results show that the relative increase in [11C]raclopride uptake in the striatum contralateral to the symptoms as compared with the opposite striatum will be preserved even during the progression of the disease, provided that the symptoms show clear-cut asymmetry.