The factor structure of the UPDRS motor scores changes during early Parkinson's disease

The factor structure differs in early versus more advanced PD, but resembles the factor structure of more advanced PD after three years. This is likely due to a higher proportion of subjects with unilateral motor symptoms in early stages of PD together with a changing distribution of motor symptoms with further disease progression. Initiation of PD medication did not alter the factor structure in early PD. The axial factor was the most consistent factor in early PD and could be the most appropriate factor to monitor progression across the earliest stages of PD.