(A) Assessing disease modification versus symptomatic benefit using compound washout. Black line represents placebo, blue line represents a disease-modifying therapeutic, dashed light blue line represents a symptomatic therapeutic such as L-DOPA, red arrow represents a change in UPDRS. (B) Using time to initiation of symptomatic treatment as an end point in PD clinical trials. Black line represents placebo, blue line represents a disease-modifying therapeutic, red arrow represents the change in time required for the initiation of symptomatic treatment.