Unmet medical needs in Parkinson's disease.

Levodopa, introduced in the late 1960s, was the first highly effective drug for the symptomatic treatment of Parkinson's disease (PD) and remains the mainstay of pharmacologic treatment. However, long-term treatment has important limitations. The disease continues to progress despite treatment with levodopa, and a neuroprotective therapy is urgently required. In addition, motor complications associated with chronic levodopa therapy are an important source of disability. Treatment of these complications forms a major focus of modern PD management, and it is in this area that recent advances in our knowledge offer the best opportunity for therapeutic gain. In the search for improved therapies, suitable outcome measures to better assess overall disability in PD and disease progression are essential.