How would you approach the consideration of a levodopa trial in an older adult with a history of schizophrenia, stable on antipsychotic medication, who has changes consistent with drug-induced Parkinsonism vs Parkinson's disease?

The first step is to establish if it is degenerative Parkinsonism, such as Parkinson's disease (presynaptic dopaminergic loss) or drug-induced Parkinsonism DIP (due to postsynaptic dopaminergic blockade). I will order a DaT scan to differentiate between the two. If the DaT scan is abnormal, I will start Sinemet cautiously. If DaT scan is normal, then it suggests DIP, and in that case I will not try Sinemet.

If DaT scan is not available, then I would do a cautious trial of Sinemet 25/100 TID and ...