Asymmetry at Disease Onset Is Not a Predictor of Parkinson's Disease Progression

Background: Even though a significant fraction of Parkinson's disease (PD) patients presents with only minor or no motor asymmetry, the motor symptoms in PD typically start on one side of the body and worse symptoms on the side of the disease onset usually persist long after the disease has become clinically bilateral. The asymmetric presentation of PD has been studied over the years, with some studies showing slower progression in PD subjects with asymmetric disease presentation. In other studies, however, it was not possible to relate the asymmetry to disease progression. Objective: The main objective of the present study was to assess the effect of asymmetry at disease onset on disease progression. Methods: Using the data available in the Parkinson's Progression Markers Initiative (PPMI) database, at baseline, 423 subjects with de-novo PD were included in the study. Instead of dichotomizing the subjects in asymmetric and symmetric, we kept the asymmetry index and the non-motor, disability, and motor progression at one-, three-, and five-year follow-up continuous. Pearson's r correlational analysis and the coefficient of determination R2 were used to correlate asymmetry indices and disease progression. Results: There was no correlation between neither clinically, nor DatSCAN defined asymmetry and non-motor, motor, and disability progression in the de-novo PD subjects with a 5-year follow-up. Conclusion: Asymmetry at disease onset does not predict progression of PD. Further studies are needed to investigate whether early detection of asymmetry on clinical grounds could successfully distinguish between PD and symmetric types of atypical parkinsonism in the early stages of the disease.