Possible impact of dopamine SPECT on decision-making for drug treatment in Parkinsonian syndrome

Summary. Single-photon emission computed tomography (SPECT) markers allow measuring the integrity of the brain dopaminergic system in vivo. We used dopamine transporter (DAT) SPECT with [¹²³I]FP-CIT and dopamine D₂/D₃ receptor SPECT with [¹²³I]IBZM to evaluate whether there is a reduction of DAT and/or D₂/D₃ receptor SPECT in treated and untreated patients with Parkinsonian syndrome (PS). We found that almost a quarter of our patients treated with anti-Parkinsonian medication prior to SPECT imaging did not show evidence of a presynaptic dopaminergic deficit while 37% of untreated patients were diagnosed as having Parkinson’s disease. 17% of treated patients had additional loss of D₂/D₃ receptor binding capacity in concordance with the clinical follow-up diagnoses of multiple system atrophy, progressive nuclear palsy, and vascular Parkinsonism. Apart from 38% clinically uncertain cases, SPECT was in concordance with 75% of initial clinical diagnoses. 25% were reclassified as indicated by SPECT findings and confirmed by a 1.5-year clinical follow-up. We conclude that dopamine SPECT may support establishing or refuting the clinical diagnosis and, therefore, help to make the decision for or against dopaminomimetic treatment in cases with PS.