When should we order a DaT scan in patients suspected of Parkinsonism syndrome?

I believe that a good clinical examination can tell you if a patient has parkinsonism or not and that is the same answer one gets from a DaTscan. If the findings are too subtle, then re-examine the patient at intervals. So my answer is it is not necessary. I emphasize "my" answer because not everyon...

When it is difficult to differentiate between essential tremors and mild Parkinson's disease, especially when no definite signs of Parkinson's are present I will order a DAT scan.