The effect of dopamine agonist therapy on dopamine transporter imaging in Parkinson's disease

Single-photon emission computed tomography (SPECT) imaging with the dopamine transporter ligand, [¹²³I] β-CIT (2β-carboxymethoxy-3β-[4-iodophenyl] tropane), has been proposed as a means of measuring Parkinson's disease (PD) progression. To be useful in this role, however, [¹²³I] β-CIT imaging should not be influenced by the medications used to treat PD, including the dopamine agonist drugs such as pergolide. We assessed the effect of adjunctive pergolide administration on [¹²³I] β-CIT uptake in 12 patients with PD, who were being treated with levodopa, initiating pergolide therapy for motor fluctuations. Patients underwent [¹²³I] β-CIT imaging at baseline, subsequently while on pergolide therapy (6 weeks), and again 4 weeks after pergolide wash-out. Uptake in the striatum was averaged for the two sides and expressed as (striatum - occipital)/occipital, with similar calculations for putamen and caudate. Consistent with PD, the patients' mean striatal and putamen uptake ratios at baseline were significantly less (p < 0.001) than the mean values from 26 normal control subjects of similar age. During pergolide treatment, the striatal and putamen [¹²³I] β-CIT uptake ratios were each statistically similar to baseline, although there was a slight trend toward an increased striatal value (8% higher on pergolide; p = 0.105). Caudate [¹²³I] β-CIT uptake was 11% higher on pergolide therapy (nominal p = 0.042, but not significant when adjusted for multiple comparisons: p = 0.126). After pergolide washout, the striatal, putamen, and caudate uptake ratios did not differ from baseline. Therefore, we found that pergolide therapy did not significantly affect [¹²³I] β-CIT SPECT imaging but we cannot exclude a small influence.