Therapeutic development paths for cognitive impairment in Parkinson's disease: report of a regulatory roundtable.

Cognitive impairment is a common occurrence in Parkinson's disease (PD), although the severity and specific presentation varies across patients. Initial deficits, including mild cognitive impairment (PD-MCI), may remain stable or in many cases, may progress over variable lengths of time to Parkinson's disease dementia (PDD). As there are currently no marketed treatments for milder forms of cognitive impairment, an opportunity exists to define the path for therapeutic development in this area. In the absence of a well-defined path for the approval of therapies that target PD-MCI, pharmaceutical companies are unlikely to pursue this indication. In order to move forward and improve the quality of life for PD patients, it is imperative for the field to have consensus on the definition of PD-MCI, the best instruments to measure cognitive decline, and a strategy for future clinical trials.