Identifying clinical measures that most accurately reflect the progression of disability in Parkinson disease

•Various dimensions of disability declined at distinct rates over 2-years in PD.•The steepest declines occurred in gait, gait-related balance and motor impairments over a 2-year period.•Declines in gait speed and gait-related balance are important markers of disability.•Early treatment to reduce gait related disability in PD is warranted.