New and emerging therapies for Parkinson disease.

Few neurological disorders have been more successful in introducing novel therapies than Parkinson disease (PD). However, despite enormous progress, many challenges remain. Although levodopa is still the most effective drug in the symptomatic treatment of PD, adverse effects, particularly motor fluctuations and dyskinesias, limit its usefulness. Furthermore, there is a growing concern about the escalating cost of PD treatment: the cost-benefit aspect of the novel approaches must be balanced against the advantages of long-term experience with established treatments.