Laterality of Motor Symptom Onset, Disease Progression, and Cognition in Parkinson's Disease

The current study examined whether laterality of initial motor symptom onset (left-sided onset vs. right-sided onset) in Parkinson's disease (PD) would predict the pattern and/or severity of cognitive deficits measured at various stages of disease progression. We evaluated the relationship between initial motor presenting symptoms obtained at the time of PD diagnosis and current cognitive profiles across three different patient groups (early unilateral, late unilateral, late bilateral stages of PD). Findings lend some support for study hypotheses regarding a lateralization of cognitive deficits based on initial laterality of motor symptoms. That is, right-sided motor symptom onset in PD was associated with diminished performance on left hemisphere cognitive measures, but the data did not reveal a significant relationship between left-sided motor symptom onset and impairment on right hemisphere measures. The current study also revealed cognitive deficits consistent with hypothesized effects of disease progression, such that cognitive changes during the unilateral stages of PD seem restricted to executive dysfunction, whereas bilateral disease in PD (with greater than 5 years disease duration) is associated with more widespread cognitive decline