123I-iodobenzamide SPECT is not an independent predictor of dopaminergic responsiveness in patients with suspected atypical parkinsonian syndromes

The prediction of dopaminergic responsiveness in patients with parkinsonism is desirable for effective treatment strategies. We investigated whether striatal dopamine D2/D3 receptor (D2R) binding assessed by 123I-iodobenzamide SPECT is an independent predictor of dopaminergic responsiveness in patients with parkinsonism. Methods: Seventy-eight patients with clinically suspected atypical parkinsonian syndrome (APS) were prospectively recruited for imaging. To quantify striatal D2R binding, 123I-iodobenzamide SPECT datasets were subjected to an observer-independent, regions-of-interest analysis. A final clinical diagnosis of Lewy-body disease (LBD) or APS was made after a mean follow-up of 12 mo. On the basis of follow-up data, dopaminergic responsiveness was classified as 0 (none), 1 (transient), 2 (sustained mild), or 3 (sustained strong). Uni- and multivariate analyses of the relationship between treatment response, D2R binding, and confounding variables were conducted. Results: Sixty patients with clinically verified LBD (n = 28; 22/28 with Parkinson disease) or APS (n = 32), in whom dopaminergic responsiveness could be assessed (n = 19/13/15/13 in categories 0/1/2/3; 18 were excluded because of insufficient dosing), were included in the statistical analysis. Univariate analyses revealed that a sustained treatment response was significantly associated with higher D2R binding, clinical diagnosis of LBD, lower Hoehn and Yahr scores, and younger age. After multivariate correction of D2R binding for diagnosis, age, symptom duration, Hoehn and Yahr score, and dopaminergic pretreatment, no association was found between D2R binding and treatment response, either in the pooled group or in LBD or APS subgroups. Conclusion: Striatal D2R binding assessed by 123I-iodobenzamide SPECT does not provide additional predictive information about treatment response beyond other clinical variables, most notably the clinical diagnosis.