Parkinson disease - Handedness predicts asymmetry

Objective: To determine the proportion of individuals in a clinic-based setting that present with asymmetric Parkinson disease (PD) and identify predictive factors associated with asymmetric symptoms. Methods: The authors examined right vs left difference scores on the Unified Parkinson Disease Rating Scale motor subscale in a consecutive clinical series of 1,277 individuals diagnosed with PD. Predictors of asymmetry included sex, symptomatic disease duration, age at onset, initial motor symptom laterality, handedness, and medical history variables ( e. g., family history of PD). Results: Nearly half the sample (46 %) met criteria for asymmetric disease based on a right vs left difference score of >= 5 points, and 12 % of the sample had a difference score of >= 10 ( difference score: mean >= 4, SD = 3.4). All three cardinal features of PD showed characteristics of asymmetric disease presentation. Multiple regression analyses showed that an increased discrepancy between right- and left-sided symptoms was significantly associated with a shorter disease duration, younger age at symptomatic onset, asymmetric initial symptom onset, hand dominance, and a positive self-reported family history of other'' neurodegenerative disorder. Hand dominance was related to the side of asymmetric disease such that left-handed individuals tended to have more severe disease on the left side of the body. Conclusion: Asymmetric presentation of Parkinson disease features was a common occurrence in the clinical cohort. Asymmetry was reliably predicted by several clinical characteristics, although the moderate level of explained variance (i.e., between 16 and 23 %) highlighted the need for additional research examining predictive models of asymmetric disease. Recommendations for the classification and measurement of asymmetric disease are discussed.