Is DaTSCAN really needed for accurate Parkinson’s disease diagnosis?

The evaluation of a new neuroimaging technique intended to be implemented for diagnosis in clinical practice requires a careful analysis of its clinical value and costs. Adequate testing against a wellestablished gold standard is a first step, which must be followed by the identification of appropriate target populations and the quantification of potentially associated risks. Cost– effectiveness assessments, including cost-utility analysis, where clinical value and costs need to be balanced, are of paramount importance as they will help decide where to allocate limited healthcare resources, providing estimates of the practical utility of the technique under evaluation. Special consideration must be paid to the possibility that estimates derived from experimental data could be too optimistic compared with those obtained in the usual clinical setting. In addition, substantial variations are expected to occur across different clinical environments. The implementation of DaTSCAN as a diagnostic tool in Parkinson’s disease (PD) missed all these important steps. First, it was approved in Europe in 2000 [101] without any formal testing of its clinical value. At that time, there was not a single PD case with pathological validation of neuroimaging findings [1]. DaTSCAN was simply taken as face-value truth. The enthusiasm of a number of leading specialists in the field of PD certainly played a fundamental role in its rapid dissemination and consolidation as a diagnostic tool. In contrast, many experts in neuroimaging were (and still are) substantially less optimistic [2,3]. Thus, in 2005, an expert panel of independent consultants concluded “current evidence does not support the use of [radiotracer] imaging as a diagnostic tool in clinical practice” [3]. Second, target populations were (and still are) poorly defined. As diagnostic uncertainty is typically maximal in the early stages of the disease, subjects with a recent diagnosis of PD are presumably the ones who could potentially benefit the most, but only if DaTSCAN results indeed represent the truth (i.e., if the results truly reflect presence or absence of dopaminergic deficit [4]). As explained below, the latter does not always hold true, which can lead to serious problems in patient management. In fact, there is evidence to suggest that therapeutic strategies based solely on imaging reports might result in missing opportunities for much needed treatment [5]. Rather paradoxically, DaTSCAN seems to be better suited to identify normal image patterns in subjects clinically diagnosed with PD than abnormal image patterns in subjects with tremor deemed not to have PD on clinical grounds [4,5]. Most of the disagreement between clinical diagnosis and DaTSCAN refers to subjects with a clinical diagnosis of PD who have normal DaTSCAN findings. The rest (a minority of cases) corresponds to subjects with a clinical diagnosis of non-PD tremor who turn out to have abnormal DaTSCAN [4,5]. Consequently, patient management guided by imaging findings will lead to missing opportunities for therapy whenever a normal imaging Is DaTSCAN really needed for accurate Parkinson’s disease diagnosis?