LAUSR

In response to the interesting article by Oravivattanakul et al. in Movement Disorders Clinical Practice, I would like to say that in the majority of centers in the UK, the method of estimation of radiotracer uptake is a mixture of qualitative and semiquantitative ones unlike only visual assessment as mentioned in the article by Oravivattanakul et al. The researchers mentioned asymmetrical uptake in the caudate nucleus and putamen, but did not state whether any classification of the abnormal uptake was used while interpreting the dopamine transporter (DaT) scan. Many centers in Europe follow the classification of abnormal tracer uptake proposed by Benamer et al. The midbrain stroke or Virchow Robin space can potentially interfere with the scan outcome. Given that the radiologists were blinded to the prescan diagnosis, it would be interesting to know whether the availability of a pre-DaT morphological brain imaging, such as CT or MRI, would have made the DaT interpretation different in cases of basal ganglia or midbrain infarction (if any). There has been an increase in the use of DaT scan in distinguishing Lewy body dementia (LBD) from non-LBD in the UK because of its high diagnostic accuracy in a large metaanalysis. Did the researchers suspect any LBD from the history before the DaT imaging given that apparently LBD was not the indication for any DaT scan in the above study? Another interesting observation in the study was the need for levodopa in a DaT-negative drug-induced parkinsonism. There are some anecdotal reports suggesting that certain drugs can unmask preclinical parkinsonism, and the relationship between the suspected drug withdrawal and resolution of parkinsonism is not straightforward. The availability of a postsynaptic DaT scan would answer some questions regarding drug-induced parkinsonism. Like the authors mentioned, indeterminate DaT scan outcome is not an uncommon occurrence in many centers in the world, including ours. The large cost of the scan remains a major reason for very few follow-up imaging studies on indeterminate scans.