Nature and Laterality of Motor Symptoms in Parkinson's Disease and Relationships to Cognitive Profile

Abstract

Previous research suggested that the nature (bradykinesia, rigidity, or tremor) and laterality (left or right-sided) of motor symptoms in Parkinson's disease (PD) are related to cognitive-linguistic profile later in the progression of the disease. Approximately 600 individuals with PD recruited through the Pacific Northwest Udall Center (PANUC) PD Registry were considered for participation. Individuals completed a neuropsychological test battery that assessed language, memory, visuospatial function, and executive function. Three logistic regression models using the same set of input variables were run: a binomial model comparing left versus right side of onset, a binomial model comparing the type of onset symptom, and a multinomial model comparing the right onset group with tremor as the predominant symptom against the three other subgroups defined by laterality and symptom type. In all three regression models, the selected cognitive variables were regressed on subgroups determined by laterality and nature of initial motor symptoms. These subgroups were left bradykinesia/rigidity onset (L-B/RO), left tremor onset (L-TO), right bradykinesia/rigidity onset (R-B/RO), and right tremor onset (R-TO). Chi squared tests revealed that the four subgroups were equivalent with respect to sex, years of education, disease duration and disease severity. Groups were significantly different with respect to age at initial neuropsychological testing, age at disease onset, and Geriatric Depression Scale total score, and these variables were entered as covariates in the regression. Overall, the regression models did not significantly differentiate the left-onset group from the right-onset group or the tremor group from the bradykinesia/rigidity group. However, the regression model with subgroups based on the combination of laterality and symptom type was found to significantly differentiate the L-TO, L-B/RO and R-B/RO subgroups from the R-TO subgroup. This finding suggests that the interaction of laterality at disease onset and nature of motor symptoms is significantly associated with the cognitive-linguistic profile of individuals with PD.